Males of the Ngogo community on patrol. (Photo by John Mitani)

Human Impacts

Our recent paper on lethal aggression (Wilson et al., 2014) has attracted lots of attention, most of it positive. Not surprisingly, though, some critical responses have also emerged. Copied below is our response to one of these critiques.

John Horgan at Scientific American devoted a blog post to critiquing the paper — though this critique is not really focused on the paper, but on whether the paper’s findings support what Horgan calls the “deep roots theory of war.” Horgan later published a critique by Brian Ferguson, the main advocate of the Human Impacts Hypothesis. In introducing this critique, Horgan offered to post responses from any of the original paper’s authors. We therefore have written a response, which is now posted here. In case it might be useful, I’ve copied it here as well:

Human impacts are neither necessary nor sufficient to explain chimpanzee violence (or bonobo non-violence)

Michael L. Wilson, Christopher Boesch, Takeshi Furuichi, Ian C. Gilby, Chie Hashimoto, Catherine Hobaiter, Gottfried Hohmann, Kathelijne Koops, Tetsuro Matsuzawa, John C. Mitani, David Morgan, Martin N. Muller, Roger Mundry, Anne E. Pusey, Julia Riedel, Crickette Sanz, Anne M. Schel, Michel Waller, David P. Watts, Frances White, Roman M. Wittig, and Richard W. Wrangham[1]

In response to our recent paper (Wilson et al., 2014), Brian Ferguson (2014) critiques the methods we used to test whether chimpanzee violence is the result of human impacts. As Joan Silk notes in her commentary on our paper, “These results should finally put an end to the idea that lethal aggression in chimpanzees is a non-adaptive by-product of anthropogenic influences — but they will probably not be enough to convince everyone” (Silk, 2014: 321).

We expect that for the majority of primatologists, and among the wider community of animal behavior researchers, the results of our study are neither surprising nor controversial. But for those hostile to the idea that human violence relates in any way to biology or adaptive behavior, the Human Impacts Hypothesis (HIH) offers an out. Violence among our ape cousins is, in this view, the result of human contact, not the result of evolution favoring aggression as a strategy. The argument closely parallels Ferguson’s earlier argument that violence in tribal societies is mainly the result of contact with outsiders, especially European imperialists (Ferguson, 1990).

In contrast to some critics, Ferguson recognizes that “there is no question that chimpanzees have the capability to make war and have done so on occasion” (Ferguson, 2011: 249). Ferguson’s critiques thus represent a departure from what we might call the “strong anti-adaptationism” of previous proponents of the HIH. For example, Power (1991) argues that chimpanzee violence is a non-adaptive response to frustration caused by restrictive feeding methods at the first long-term study sites of chimpanzees, Gombe and Mahale. Ferguson embraces Power’s hypothesis that feeding chimpanzees made them more violent, but in contrast to Power, he argues that chimpanzee violence is mainly the result of resource competition, which is exacerbated by human activities such as feeding and deforestation. This argument differs little from arguments that behavioral ecologists regularly make to explain chimpanzee violence. For example, intercommunity violence in chimpanzees is strongly associated with competition over food resources. At Kanyawara, intercommunity encounters occurred most frequently when key food species were abundant in areas bordering neighboring communities (Wilson et al., 2012). Lethal aggression is strongly associated with territorial expansion at Ngogo (Mitani et al., 2010) and Gombe (Goodall, 1986), and by expanding territory chimpanzees increase the amount of food available to themselves, their mates and offspring (Williams et al., 2004; Pusey et al., 2005).

However, in his critique, Ferguson seems to conflate “resource competition” with “disturbance brought about by the actions of people.” Resource competition is not necessarily a “disturbance”, nor does it occur only as a consequence of “disturbance.” Instead, resource competition is a routine part of existence for living things. This is one of the central premises of evolution by natural selection, and evolutionary disciplines such as behavioral ecology. Ferguson therefore appears to agree with us that violence is an adaptive strategy for resource competition. And we agree that actions of people can sometimes affect resource competition in other animals, for example by adding a valuable, concentrated resource (Wrangham, 1974), or by removing key resources such as fruit trees, increasing competition for available land (Goodall, 1977). What we disagree on is whether the evidence indicates that human impacts are the main cause of chimpanzee violence.

Ferguson argues that “human impact must be approached in historical detail.” The 30 co-authors of our paper are deeply familiar with the historical details, with many of them having been involved in these long-term sites for decades. But historical awareness does not preclude a scientific approach. Clear predictions emerge from the hypothesis that human impacts cause chimpanzees to kill. We have sought to test those predictions systematically. We also appreciate that our study sites and study populations, and the human populations that now surround those sites, have complex histories that long pre-date our research projects, and that we should be aware of this fact despite the difficulties of reconstructing these histories. However, we are also concerned with history in another sense: the evolutionary history of chimpanzees. For the great majority of this history, chimpanzees and their immediate ancestors could not have been subject to “disturbance” of the kinds that Ferguson and other proponents of the HIH invoke.

When introducing Ferguson’s critique, John Horgan writes of confirmation bias, which is indeed a concern in any scientific endeavor. To counter this bias, scientists use tools such as collecting quantitative data and using statistical methods to test which models best explain the observed data. In our study, we sought to use methods that are objective and transparent, and which would provide well-substantiated answers, whether they agreed with our prior opinions or not.

In contrast, the “holistic” approach promoted by Ferguson is vulnerable to confirmation bias. Without clearly defining variables such as disturbance, and without using quantitative data and statistical methods designed to test whether a given set of results is likely given the available sample size, efforts to compare contrasting interpretations of a given set of data risk degenerating into cherry picking and special pleading.

Ferguson argues that “[t]he three measures Wilson et al. created to test for human impact are questionable.” However, he agrees in principle with each of these measures, and offers no quantifiable alternatives.

He states that our first measure, “artificial provisioning of food, is good, where it applies, though the impact of provisioning varies by how it is carried out and other conditions of food availability.” By this Ferguson presumably refers to the argument of Power (1991) that the “restricted” provisioning at Gombe and Mahale is what frustrated chimpanzees and (in Power’s view) fundamentally changed their behavior.

We do not dispute that providing food can change the behavior of chimpanzees and other animals. Wrangham (1974) found that at Gombe, chimpanzees and baboons were more aggressive in the feeding area than when foraging for natural foods away from the feeding area. What is clear from our study, however, is that provisioning is neither necessary nor sufficient for chimpanzees to kill.

We examined data on both chimpanzees (18 communities at 10 study sites) and bonobos (4 communities at 3 study sites). Of these sites, provisioning occurred at two chimpanzee sites (Gombe and Mahale) and one bonobo site (Wamba).

Evidence for lethal aggression has been found in seven of the of eight never-provisioned study sites (Budongo, Fongoli, Goualougo, Kalinzu, Kibale, Kyambura, Taï); the only exception is the small, isolated population at Bossou. Ferguson notes that “sites marked P for provisioning cluster (4 out of 7 cases) toward the high end of the killing distribution.” Fair enough, but the two highest rates of killing are for sites where chimpanzees were never provisioned. Moreover, at Mahale and Gombe, killings have continued to be observed long after provisioning ended (in 1987 and 2000, respectively). Killings by never-provisioned chimpanzees have also been reported at shorter-term study sites not included in our study, including Loango in Gabon (Boesch et al., 2007), as well as Conkouati-Douli National Park, Congo, where male wild-born, captive chimpanzees released into the wild were attacked by resident chimpanzees (Goossens et al., 2005).

Ferguson claims that “Provisioning’s statistical association with killing, however, is diluted by two other sites,” Mahale’s K-group and Wamba. “Diluted” is an odd choice of words here; if provisioning causes chimpanzees to become violent, then presumably every community provides relevant data, rather than dilution. Excluding K-group from the analysis would involve picking and choosing, excluding any data that doesn’t fit the expectation (in other words, guaranteeing confirmation bias).

Provisioning is thus clearly not necessary for chimpanzees to kill. Nor is it sufficient for killing to occur. Killings have been observed at both of the historically provisioned chimpanzee sites, but the observed and inferred killings by the Mitumba community at Gombe occurred only after provisioning ended there (Wilson et al., 2004). (We note, though, that one infanticide is suspected to have occurred at Mitumba during the time that Mitumba chimpanzees were provisioned (Pusey et al., 2008)).

Killings have not been observed at the provisioned bonobo site (Wamba). The one suspected bonobo killing took place at a non-provisioned site (Lomako). Ferguson notes that bonobos are a different species. Of course, this is true. But if provisioning causes chimpanzees to kill, why should it not cause other species to kill, especially closely related species?

Ferguson argues that Wamba should not be included in the analysis because bonobos are a different species. Fair enough; and indeed, in Table 3, we present results focused on just chimpanzees, excluding bonobos, and found that provisioning history did not explain variation in rates of killing among chimpanzee communities. But we also note that Ferguson has previously written that violence in chimpanzees is the result of social learning, proposing that bonobos would behave like chimpanzees if they experienced similar conditions (“What would happen if a bonobo were raised among chimpanzees or vice versa? I expect their behaviors would reflect the local custom” (Ferguson 2011: 255)). Following this line of logic seems to suggest to us that exposing bonobos to the same stimulus as chimpanzees (provisioned food) should result in a similar increase in aggressive behavior. But the one suspected case of killing by bonobos occurred at the never-provisioned site of Lomako, rather than the provisioned site of Wamba.

In our view, the much less frequent occurrence of violent aggression in bonobos compared to chimpanzees raises interesting questions about the evolution of non-violence as well as violence.

We note with interest, though, that Ferguson’s argument for provisioning is profoundly different from Power’s argument. Power argued that restricted provisioning fundamentally changed the behavior of chimpanzees at Gombe and Mahale, and that a wide range of chimpanzee behaviors reported by researchers there were the result of provisioning: male dominance hierarchies, despotic alpha males, possessive sexual behavior, closed membership of social groups, territorial behavior, female dispersal, hunting of monkeys, and intergroup killings. Studies of never-provisioned chimpanzees have found that all of these behaviors occur in the absence of provisioning. We can therefore reject the idea that chimpanzee behavior is fundamentally altered by provisioning. And indeed, instead of following Power’s argument that chimpanzee violence is maladaptive, Ferguson accepts that chimpanzee violence is an adaptive component of resource competition.

As a second measure of human impacts, we examined size of protected area. Ferguson notes that “some chimpanzee groups living within large protected areas have been heavily impacted.” Fair enough. That is why we conducted multivariate analyses considering several different variables. However, size of protected area is a measure that is readily quantified, and is likely important both for chimpanzee conservation and as a general measure of the degree to which chimpanzees have been affected by human activities. Like our other measures of human disturbance, however, size of the protected area did not have a consistent effect on rates of violence.

Our third measure of human impacts was an index of disturbance, based on a method developed by Naomi Bishop and colleagues for assessing the impacts of human activities on Hanuman langur monkeys in India (Bishop et al., 1981). Ferguson agrees that these measures “work well as a general index of over-all human impact,” but complains that “they do not work as predictors of intensified violence.” Similar complaints could be made of any effort to quantify human disturbance, because what exactly qualifies as disturbance is never clearly stated. However, it is worth pointing out that the disturbance index developed we used was originally developed to address a controversy over causes of infanticide (Bishop et al., 1981).

Importantly, for our disturbance rankings, each site director ranked their own site without prior knowledge of the rankings of other researchers. These rankings thus provide an independent estimate of disturbance made by the people who best know each of these sites.

Ferguson notes that Budongo has been exposed to various forms of lumber extraction, and other chimpanzee sites have experienced “islandization.” Fair enough. As primatologists actively involved in conservation efforts, we are deeply familiar with such issues at our sites. Capturing all of these different effects in a single variable, or a single index that combines several measures of disturbance (the approach we used), can never be wholly satisfactory. But we believe that the rankings that we did for our study do correlate reasonably well with the degree to which these different sites have been affected by humans. Goualougo is clearly the least affected chimpanzee site, and Bossou the most. Kanyawara, at the edge of Kibale National Park, has a higher disturbance rating than Ngogo, at the center of the park. We do not argue that our index is perfect, but we are not aware of a better one.

Ferguson points to many different possible impacts: provisioning, habitat clearance, timber extraction, hunting, and so on. Some of these could well have an effect on chimpanzee violence, by (for example) increasing the intensity of competition for resources. This is an adaptationist argument following standard theory in behavioral ecology, and as such, is an approach that we find reasonable. It is the fact that these are reasonable questions that motivated us to conduct our study. Given the possibility that human activities can affect rates of violence in chimpanzees, it is important to investigate the extent to which the observed patterns of violence reflect human impacts. This is what we have attempted to do, using data that are quantifiable, systematic, defined using the same criteria across study sites, and using a statistical approach that allows us to test predictions from multiple contrasting models. We found that human impacts did not explain the variation in rates of lethal aggression as well as other factors. Eastern chimpanzees killed more often than western chimpanzees, which killed more often than bonobos. Communities with more males and communities living in denser populations killed more frequently than communities with fewer males and sparser populations.

It is not at all clear why chimpanzees should react this way when exposed to humans, but not bonobos, baboons, or other species. For example, baboons have been studied at Gombe almost as long as chimpanzees and have been influenced by human activity. But they have not been observed to participate in coalitionary killing. What accounts for such differences between species when exposed to precisely the same human impacts? The absence of coalitionary killing in baboons makes sense from an evolutionary perspective (Wrangham, 1999), but is inexplicable from an anti-adaptationist perspective.

Moreover, chimpanzees and humans are far from the only species to engage in lethal aggression. Fatal fighting occurs widely among animals, and includes a broad range of examples, such as fatal fights among male spiders competing for mating opportunities (Leimar et al., 1991) and the killing and consumption of male spiders by female spiders, after (or sometimes during or even before) the males have mated (e.g., Andrade, 1996). Most such fatal fighting involves fights between individuals over a highly valuable resource. In contrast, coalitionary killing occurs in fewer species, and seems mainly limited to certain social insects, social carnivores such as wolves, lions and spotted hyenas, and a few primates, including humans and chimpanzees (Wrangham, 1999). Why coalitionary killing occurs in these species but not others is explicable, in principle, using the comparative method to develop testable hypotheses. An anti-adaptationist approach promises no such explanatory power.

Whether chimpanzee violence is adaptive or not, is a question for which we do not yet have a definitive answer. Answering this question in full requires information on reproduction and information on individual participation in violence, which is available for only a few sites and which has not yet been analyzed. Additionally, chimpanzees (like humans and other animals) may sometimes make mistakes, participating in killings that result in fitness (i.e. reproductive) costs. Whether a given behavioral strategy is adaptive depends on average effects of traits. Given these caveats, previous studies provide evidence in support of the view that chimpanzee violence provides fitness benefits to the attackers. Mitani et al. (2010) found that the intergroup killings by the Ngogo community were associated with substantial territorial expansion in the area where disproportionately many of the killings had taken place. Studies at Gombe provide evidence that larger territories provide important fitness benefits, including more food, as indicated by heavier individual body weights, controlling for age and reproductive condition (Pusey et al., 2005) and shorter inter-birth intervals for females (Williams et al., 2004). Males who enlarge their territory thus provide more food for their mates and offspring, enabling faster reproduction, and thus greater reproductive success for the aggressors.

In his critique, Ferguson mostly ignores the second focus of our paper: the pattern of attackers and victims. We found that most participants (92%) were male, as were most victims (73%). Most victims were members of other communities (63%). Intercommunity killings generally involved gang attacks, in which attackers outnumbered victims by a factor of 8:1. These patterns make sense when seen as adaptive strategies. Male chimpanzees defend group territories; eliminating members of rival communities enables males to increase the amount of food available to themselves, their mates, and offspring (Williams et al, 2004; Pusey et al., 2005; Mitani et al., 2010). Chimpanzees prefer to attack when the odds are in their favor (Wrangham 1999; Wilson et al., 2012). Viewing these behaviors solely as a non-adaptive response to human disturbance provides no insights into why attacks mainly involve males attacking members of other groups when the odds are in their favor.

The question of what, if anything, chimpanzee violence has to do with human warfare is one we did not address in our paper. We expect that among our 30 co-authors some diversity of opinion exists on this topic. We would all agree, though, that definitive claims about human behavior need to be based on data from humans.

Nonetheless, there are some important things we can learn from chimpanzee studies. Our study examines lethal aggression broadly, including infanticide and within-community violence. Despite this, the criticisms of Ferguson (as well as John Horgan’s earlier post) focus mainly on intercommunity killing, and its relevance to studies of human warfare. Ferguson, Horgan, and many others argue that warfare has a relatively recent origin (within the past 10,000 years (Ferguson, 2003)), due to some relatively new phenomenon, such as agriculture, or settled societies, or food storage, or property rights, or ideology, or new kinds of weapons. Chimpanzees have none of these things. They do sometimes use weapons (sticks and stones) but they don’t generally use them to kill each other. So the documentation of warlike behavior in chimpanzees shows that similar behavior could have occurred in humans long before the origin of agriculture and other evolutionarily recent innovations. It also raises the intriguing possibility that humans and chimpanzees share similar patterns of violence due to our shared evolutionary history; we may have inherited these patterns of behavior from our common ancestor.

As many have noted, however, and as we fully recognize, the existence of bonobos, with their much less violent societies, highlights the need to be cautious in how much we infer along these lines. It is possible that the lineages leading to humans and chimpanzees have both become more violent, or that the lineage leading to bonobos has become more peaceful over evolutionary time. We don’t yet know the answer to this question.

We heartily agree with Silk’s point that “Humans are not destined to be warlike because chimpanzees sometimes kill their neighbours” (Silk, 2014: 322). Variation in rates of warfare among countries today, and across historical time, clearly show that people can develop institutions and mechanisms that reduce the frequency and severity of warfare (Gat, 2006; Pinker, 2011). Chimpanzee communities also vary considerably in their rates of intercommunity violence. As we have found, this variation is better explained by differences among species, populations, and demography than by human impacts (Wilson et al., 2014).

References

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Bishop, N., S. B. Hrdy, J. Teas and J. Moore (1981). “Measures of human influence in habitats of South Asian monkeys.” International Journal of Primatology 2(2): 153-167.

Boesch, C., J. Head, N. Tagg, M. Arandjelovic, L. Vigilant and M. M. Robbins (2007). “Fatal chimpanzee attack in Loango National Park, Gabon.” International Journal of Primatology 28: 1025-1034.

Ferguson, R. B. (1990). “Blood of the Leviathan: Western contact and warfare in Amazonia.” American Ethnologist 17(2): 237-257.

Ferguson, R. B. (2003). “The birth of war.” Natural History 112(6): 28-35.

Ferguson, R. B. (2011). Born to Live: Challenging Killer Myths. Origins of Altruism and Cooperation. R. W. Sussman and C. R. Cloninger: 249-270.

Ferguson, R. B. (2014). “Anthropologist Brian Ferguson challenges claim that chimp violence is adaptive.” Retrieved 19 September 2014, from http://blogs.scientificamerican.com/cross-check/2014/09/18/anthropologist-brian-ferguson-challenges-claim-that-chimp-violence-is-adaptive/.

Gat, A. (2006). War in Human Civilization. Oxford, Oxford University Press.

Goodall, J. (1977). “Infant killing and cannibalism in free-living chimpanzees.” Folia Primatol 22: 259-282.

Goodall, J. (1986). The Chimpanzees of Gombe: Patterns of Behavior. Cambridge, Massachusetts, Belknap Press.

Goossens, B., J. M. Setchell, E. Tchidongo, E. Dilambaka, C. Vidal, M. Ancrenaz and A. Jamart (2005). “Survival, interactions with wild conspecifics and reproduction in wild-born orphan chimpanzees following release into Conkouati-Douli National Park, Republic of Congo.” Biological Conservation 123: 461-475.

Leimar, O., S. Austad and M. Enquist (1991). “A test of the sequential assessment game: fighting in the bowl and doily spider Frontinella pyramitela.” Evolution 45(4): 862-874.

Mitani, J. C., D. P. Watts and S. J. Amsler (2010). “Lethal intergroup aggression leads to territorial expansion in wild chimpanzees.” Current Biology 20(12): R507-R508.

Pinker, S. (2011). The Better Angels of Our Nature: Why Violence Has Declined, Viking.

Power, M. (1991). The Egalitarians—Human and Chimpanzee: An Anthropological View of Social Organization. Cambridge, Cambridge University Press.

Pusey, A. E., G. W. Oehlert, J. M. Williams and J. Goodall (2005). “The influence of ecological and social factors on body mass of wild chimpanzees.” International Journal of Primatology 26: 3-31.

Pusey, A. E., C. Murray, W. R. Wallauer, M. L. Wilson, E. Wroblewski and J. Goodall (2008). “Severe aggression among female chimpanzees at Gombe National Park, Tanzania.” International Journal of Primatology 29(4): 949-973. get pdf

Silk, J. B. (2014). “Animal behaviour: The evolutionary roots of lethal conflict.” Nature 513(7518): 321-322.

Williams, J. M., G. Oehlert, J. Carlis and A. E. Pusey (2004). “Why do male chimpanzees defend a group range? Reassessing male territoriality.” Animal Behaviour 68(3): 523-532.

Wilson, M. L. (2012). Long-term studies of the Gombe chimpanzees. Long-term Field Studies of Primates. P. Kappeler and D. P. Watts. Heidelberg, Springer-Verlag: 357-384. get pdf

Wilson, M. L., C. Boesch, B. Fruth, T. Furuichi, I. C. Gilby, C. Hashimoto, C. Hobaiter, G. Hohman, N. Itoh, K. Koops, J. Lloyd, T. Matsuzawa, J. C. Mitani, D. C. Mjungu, D. Morgan, R. Mundry, M. N. Muller, M. Nakamura, J. D. Pruetz, A. E. Pusey, J. Riedel, C. Sanz, A. M. Schel, N. Simmons, M. Waller, D. P. Watts, F. J. White, R. M. Wittig, K. Zuberbühler and R. W. Wrangham (2014). “Lethal aggression in Pan is better explained by adaptive strategies than human impacts.” Nature 513: 414-417.

Wilson, M. L., S. M. Kahlenberg, M. T. Wells and R. W. Wrangham (2012). “Ecological and social factors affect the occurrence and outcomes of intergroup encounters in chimpanzees.” Animal Behaviour 83(1): 277-291. get pdf

Wilson, M. L., W. Wallauer and A. E. Pusey (2004). “New cases of intergroup violence among chimpanzees in Gombe National Park, Tanzania.” International Journal of Primatology 25(3): 523-549. get pdf

Wrangham, R. (1974). “Artificial feeding of chimpanzees and baboons in their natural habitat.” Animal Behaviour 22: 83-93.

Wrangham, R. W. (1999). “The evolution of coalitionary killing.” Yearbook of Physical Anthropology 42: 1-30.

[1] We invited all co-authors of our original paper to contribute to this response. All of those who responded to our invitation provided feedback and asked to be included as co-authors. Most (or perhaps all) of those who have not yet responded to this request are currently in the field with limited access to email. Not being included on this list, therefore, does not necessarily imply any disagreement with the contents of this response.

KONRAD WOTHE/MINDEN PICTURES/CORBIS
Pimu, an alpha male chimp at Mahale Mountains National Park in Tanzania, being killed by fellow chimps in 2011.

Chimpanzee violence

Are chimpanzees naturally violent? Or is chimpanzee violence the result of human interference, such as artificial feeding or habitat loss? Along with 29 co-authors, I  examine this question in a paper published this week in Nature.

Jane Goodall writes in her magnum opus, The Chimpanzees of Gombe:

Early field studies of chimpanzees (including my own) gave rise to the myth of the gentle, peace-loving ape. As more data on chimpanzee behavior have been collected over the years, this myth has gradually been dispelled. (Goodall 1986: 313)

Despite observations of violence in chimpanzees by Goodall and many others, a few  people still cling to the myth that chimpanzees are peace-loving apes at heart, moved to violence only by human impacts. This view was most fully developed by Margaret Power in her 1991 book, The Egalitarians—Human and Chimpanzee.

As far as I know, Power never studied chimpanzees in the wild. Instead, she based her arguments on reading the literature, especially Goodall’s early work, and also work by other people who had conducted shorter studies of chimpanzees at other sites, such as Vernon and Frankie Reynolds’ study of chimpanzees at Budongo Forest, Uganda, and Michael Ghiglieri’s study of chimpanzees at Ngogo, in Kibale Forest, also in Uganda.

Power distinguished “naturalistic” studies of chimpanzees from “provisioning” studies, in which chimpanzees were given food by researchers. This distinction follows a long tradition of researchers who have argued that Gombe chimpanzees were no longer truly “wild” after Goodall started feeding them bananas (e.g., Reynolds, 1975).

Power noted that in a 1974 paper,  Richard Wrangham showed that Gombe chimpanzees behaved more aggressively in “camp,” where researches fed them bananas,  than in the rest of their range, where they fed on naturally occurring foods. While Wrangham explained this change in behavior as a natural response to competing over an especially rich and concentrated source of food, Power developed a more elaborate argument based on psychological frustration theory, arguing that chimpanzee behavior was fundamentally changed by frustrations encountered at the feeding station.

Power argued that all sorts of chimpanzee behavior described by Goodall and colleagues, such as territorial behavior, dominance hierarchies, intense competition for mating opportunities, bullying by the alpha male, hunting of monkeys, and lethal aggression, were not natural behavior, but were instead the result of frustration caused by restrictive feeding of chimpanzees. She made the same arguments for Mahale, the study site established by Toshisada Nishida shortly after Goodall began her studies at Gombe. Nishida and his team used sugar cane to attract chimpanzees to an observation area. Power argued that this fundamentally changed their behavior, just as it had for Gombe chimpanzees. Only the earlier, “naturalistic” observations of  chimpanzees could be trusted. Power discounts all later observations from these sites, even though at both Gombe and Mahale, as chimpanzees became better habituated, researchers increasingly followed chimpanzees throughout their forest range, rather than focusing on observations at the feeding stations.

When Power published her book in 1991, chimpanzees had been studied at many different sites across Africa, but understanding of chimpanzee behavior in the wild was still very much dominated by studies from Gombe and Mahale. Nonetheless, new long-term studies were already underway at places including Taï Forest in Côte d’Ivoire and Kibale Forest in Uganda. These studies have continued, and new studies have been established at other sites. Researchers eventually stopped feeding chimpanzees at both Mahale and Gombe, and none of the newer study sites used artificial feeding to observe chimpanzees. Many of the new sites were in large, relatively undisturbed protected areas. And yet chimpanzees at all these sites demonstrated patterns of behavior that Power argued were the result of provisioning, including dominance hierarchies, bullying by alpha males, intense competition among males for mating opportunities, hunting of monkeys, and territorial behavior. These observations soundly refuted Power’s hypothesis that the behavior of provisioned chimpanzees was fundamentally different from that of unprovisioned chimpanzees.

Nonetheless, when I started studying chimpanzees in the mid-1990s, the number of detailed observations of lethal aggression in chimpanzees was still small. The most detailed accounts of killing were those from Gombe and Mahale. It seemed at the time reasonable to wonder whether those killings were the result of something unusual about those sites, such as the artificial feeding that occurred there. Or perhaps something else was responsible, such as the ecology of these sites, both located near the southeastern limits of the range of the species.

When I started graduate school, I was mainly interested  in language evolution. I wanted to do playback experiments with chimpanzees in order to test whether they had symbolic communication, like Dorothy Cheney and Robert Seyfarth had found with vervet monkeys. I went to Harvard to work with Marc Hauser, who had been a student of Cheney and Seyfarth, and Richard Wrangham, who had established a new long-term study of the Kanyawara community in Kibale.

Although my main focus was language evolution and communication, I was also inspired by two papers published in Current Anthropology:  “The human community as a primate society,” by Lars Rodseth, Richard Wrangham, and Barb Smuts, and “Intergroup aggression in chimpanzees and humans,” by Joe Manson and Richard Wrangham. The approach of these papers, seeking to explain human behavior through comparative study of other primates, seemed exactly the sort of thing we should be doing to gain a proper understanding of our species.

In 1996, I started my first field season at Kanyawara, doing a pilot study of playback experiments. These turned out to be the first successful playback experiments to wild chimpanzees — and they also ended up shifting my focus from language evolution to intergroup aggression.

We knew it would be hard to do playback experiments with chimpanzees. They are smart, and fast. We worried that playing soft calls at close range wouldn’t work easily, as they would find the speaker and catch on that something wasn’t right. So we needed to work with loud calls that would let us set up the speaker far away from the chimps. We also needed to focus on an experimental question that could be answered with relatively few trials, since we figured chimpanzees would habituate quickly to the experimental situation if we did the same thing over and over. So we settled on simulating intergroup events, playing a single pant-hoot call from a male stranger, using calls that John Mitani had recorded from chimpanzees at Mahale. This would enable us to test whether chimpanzees could assess the relative numbers of their opponents, much as Karen McComb, Craig Packer and Anne Pusey had recently shown with lions (McComb et al., 1994). As a result of choosing to do these particular experiments, I ended up shaping the rest of my dissertation research around questions of intergroup aggression.

In the fall after I had finished my first round of experiments at Kibale, Richard Wrangham and Dale Peterson published Demonic Males. This book inspired a closer look at intergroup aggression in chimpanzees. It also attracted criticism, particularly I think from people responding to the title of the book, rather than its contents. Among the more vocal critics have been Bob Sussman (1999, 2013) and Brian Ferguson (2011). Both Sussman and Ferguson have resurrected Margaret Power’s arguments that chimpanzee violence is not natural, but somehow the fault of humans.

At the same time, the evidence for chimpanzee violence continued to accumulate, not just at Gombe, but at sites across Africa. Many cases of violence have been reported from sites that were never provisioned. Critics such as Sussman and Ferguson have therefore shifted the focus away from provisioning and more towards other forms of disturbance: habitat loss, deaths from poaching and disease, and so forth.

In 2001, I finished my PhD and started working as a post-doc with Anne Pusey at the University of Minnesota. My main goal as a post-doc with Anne was to look at intergroup aggression data from Gombe, one of the very few sites where neighboring habituated communities could be studied. This provided a rare opportunity to examine intergroup aggression from both sides of the interaction.

Working at Gombe also increased my awareness of issues related to human impacts.  I ended up spending three years based at Gombe full-time, working for the Jane Goodall Institute. Conservation issues are important at every ape research site, but are particularly prominent at Gombe, given that it is a relatively small park exposed to substantial human impacts, especially deforestation outside the park. And throughout the time I have been working at Gombe, chimpanzees have, from time to time, attacked and killed one another.

In thinking about human impacts and chimpanzee violence, there are really two major issues to consider. One is whether human impacts, such as provisioning and habitat destruction, affect rates of violence. The other question is whether violence is mainly adaptive behavior or not. For example, Wrangham (1974) clearly showed that rates of aggression were higher at the feeding station than in the forest. But he argued this was a natural, adaptive response to a highly concentrated, high quality food source. Individuals who competed aggressively for bananas would get to feast on soft, easily digested fruits, rich in sugar and starch. Individuals who stayed out of the fray would go hungry, or have to go searching long distances in the forest for natural foods.

Likewise, during the decades when forests adjacent to Gombe were being cleared for farmland, it seems entirely plausible that this could lead to higher rates of violence, as chimpanzees retreated into the remaining protected area inside the park. If the number of chimpanzees in the area stayed the same, but the available habitat shrank, this could lead to increased aggression. In this case, though, increased aggression might well be a strategy by which individuals increased their reproductive success. Individuals that simply retreated, rather than defending their land, would be forced out of the good areas, while the aggressive victors would enjoy the spoils.

Critics such as Sussman and Ferguson seem mainly interested in arguing that aggressive behavior is maladaptive. They don’t like the idea that aggressors might benefit from violent behavior, and seem mainly worried about the consequences of such arguments. For example, if we argue that violent behavior is favored by natural selection, does that mean that we must then excuse violent behavior, and accept it as natural?

I think that such concerns are unjustified, however. Just because something is “natural” doesn’t mean it is desirable, or inevitable. Smallpox virus is natural, but deeply undesirable, and humans have intentionally and with great effort eradicated this virus. We have likewise made great strides towards reducing rates of warfare and other violence.

Nonetheless, whether chimpanzee violence is natural, or the result of human impacts, is an important question to get right. I have spent a number of years trying to answer it. I first presented a version of this study in 2004, in a talk at the International Society for Research on Aggression meetings in Santorini, Greece, titled: “Is chimpanzee intergroup violence the result of human disturbance?”

In this earlier effort, based mainly on the published literature, I didn’t find any strong link between human impacts and chimpanzee violence. By this time killings had been reported from several sites that had never been provisioned, including Ngogo and Kanyawara in Kibale Forest, Uganda, and Budongo, also in Uganda. But I had other things on my plate, and ended up putting this study on the back burner for several years.

It wasn’t until 2011 that I started working on the project again in earnest. Once I got started I realized that to really get a handle  on this question, published data wouldn’t be enough. I wanted to make sure that the data from each site was accurate, and that variables demographic and ranging data were all coded the same way. I wanted independent ratings of disturbance from each site. And I knew from my own experience that it can take years from the time that killings are observed to when detailed descriptions are written up and published. A study using just the published cases would result in a potentially severe underestimation of rates of violence. So I started contacting researchers at other sites and asked if they would be interested in participating. In the end the study included all the main long-term studies of chimpanzees and bonobos, and a long list of co-authors.

The main take home message of our study is that chimpanzee violence is natural behavior, not the result of human impacts. We have two main lines of evidence for this.

First, if we look across study sites, the degree of human impacts doesn’t explain the variation in rates of killing that we see. The site with the highest rate of killing, Ngogo, is in a forest with relatively low human impacts, and these chimpanzees were never artificially fed by researchers. In contrast, the site with the highest human disturbance rating, Bossou, is a site where killing has never been observed, despite many years of observation. Instead, overall killing rates are better explained by differences among species (chimpanzees kill more often than bonobos), and differences in demography (groups with more males, and that live at higher population densities, have more killing). Moreover, high population density appears to reflect good habitat quality, rather than human disturbance.

Second, if we look at the detailed patterns of who is killing whom, we see patterns that make sense from an evolutionary viewpoint, but which are hard to explain otherwise. Attackers did not kill at random. Instead, they mainly killed members of other groups (63% of killings). They mainly killed when they had an overwhelming numerical advantage (median 8:1 ratio of attackers to victims in intergroup killings). Attackers were much more often male than female (92% of participants in attacks) and they mainly killed males (73% of victims). They mainly killed when it was easy to kill victims, either because of a strong numerical advantage, or because the victim was weak (such as infants).

People often ask what the implications of this study are for human
behavior. I would say that definitive claims about human behavior need to be based on data from humans. But there are some important things we can learn from chimpanzee studies. One is that we can get much more detail on the contexts of killings in chimpanzees than is normally possible in human studies. We can watch them do everything in their daily lives, including killing — something we can’t do easily, ethically, or legally with humans. So we can collect lots of data that is useful for testing hypotheses about the biology of violence that apply to humans as well as other species. Another thing we have learned relates especially to the origins of warfare. Some people argue that warfare has a recent origin, due to some relatively new phenomenon, such as agriculture, or settled societies, or food storage, or property rights, or ideology, or new kinds of weapons, and so on. Chimpanzees have none of these things. They do sometimes use weapons (sticks and stones) but they don’t generally use them to kill each other. So the documentation of warlike behavior in chimpanzees shows that similar behavior could have occurred in humans long before the origin of agriculture and other evolutionarily recent innovations. It also raises the intriguing possibility that humans and chimpanzees share similar patterns of violence due to our shared evolutionary history; we may have inherited these patterns of behavior from our common ancestor.

The existence of bonobos, however, with their much less violent societies, highlights the need to be cautious in how much we infer along these lines. It is possible that the lineages leading to humans and chimpanzees have both become more violent, or that the lineage leading to bonobos has become more peaceful over evolutionary time. We don’t yet know the answer to this question.

 

References

Ferguson, R. B. (2011). “Born to Live: Challenging Killer Myths.” Origins of Altruism and Cooperation. R. W. Sussman and C. R. Cloninger, Eds. Springer New York. 36: 249-270.

Goodall, J. (1986). The Chimpanzees of Gombe: Patterns of Behavior. Cambridge, Massachusetts, Belknap Press.

Manson, J. H. and R. W. Wrangham (1991). “Intergroup aggression in chimpanzees and humans.” Current Anthropology 32(4): 369-390.

McComb, K., C. Packer and A. Pusey (1994). “Roaring and numerical assessment in contests between groups of female lions, Panthera leo.” Animal Behaviour 47: 379-387.

Power, M. (1991). The Egalitarians—Human and Chimpanzee: An Anthropological View of Social Organization. Cambridge, Cambridge University Press.

Reynolds, V. (1975). “How wild are Gombe chimpanzees.” Man 10(1): 123-125.

Rodseth, L., R. W. Wrangham, A. M. Harrigan and B. B. Smuts (1991). “The human community as a primate society.” Current Anthropology 32(3): 221-254.

Sussman, R. W. (1999). “The myth of man the hunter, man the killer and the evolution of human morality (evolutionary and religious perspectives on morality).” Zygon 34(3): 453-472.

Sussman, R. W. (2013). Why the legend of the killer ape never dies: The enduring power of cultural beliefs to distort our view of human nature. War, Peace, and Human Nature: The Convergence of Evolutionary and Cultural Views. D. P. Fry. Oxford, England, Oxford University Press: 97-111.

Wilson, M. L., R. W. Wrangham and A. E. Pusey (2004). “Is chimpanzee intergroup violence the result of human disturbance?” XVI World Meeting of the International Society for Research on Aggression, Fira, Santorini, Greece.

Wilson, M. L., C. Boesch, B. Fruth, T. Furuichi, I. C. Gilby, C. Hashimoto, C. Hobaiter, G. Hohman, N. Itoh, K. Koops, J. Lloyd, T. Matsuzawa, J. C. Mitani, D. C. Mjungu, D. Morgan, R. Mundry, M. N. Muller, M. Nakamura, J. D. Pruetz, A. E. Pusey, J. Riedel, C. Sanz, A. M. Schel, N. Simmons, M. Waller, D. P. Watts, F. J. White, R. M. Wittig, K. Zuberbühler and R. W. Wrangham (2014). “Lethal aggression in Pan is better explained by adaptive strategies than human impacts.” Nature 513: 414-417.

Wrangham, R. (1974). “Artificial feeding of chimpanzees and baboons in their natural habitat.” Animal Behaviour 22: 83-93.

Wrangham, R. W. and D. Peterson (1996). Demonic Males: Apes and the Origins of Human Violence. Boston, Houghton Mifflin.

Noah's Ark

Noah

Watching Darren Aronofsky’s film Noah makes me wonder: What gives this story such enduring appeal? It is scientifically implausible in all sorts of fascinating ways. The religious implications, if taken seriously, are deeply disturbing. And yet the story retains the mythic power to raise millions of dollars for its retelling, not just in Hollywood, but also in Kentucky.

In July, just a few months after the Noah film premiered, the state of Kentucky approved $18 million in tax breaks to support the building the Ark Encounter, a replica of Noah’s ark as interpreted by the Young Earth Creationist group, Answers in Genesis. Like its sister institution, the Creation Museum, the Ark Encounter will be a perverse sort of anti-museum, dedicated to ignorance and misinformation.  What is it about Noah’s story that inspires such dedication? Why would people of faith be willing to put such stake in a story for which there is no evidence whatsoever in history, archaeology, genetics, or biogeography, and which is so deeply implausible on the grounds of basic physics and planetary science?

As a kid, the Noah story was one of my favorite Bible stories – along with the Garden of Eden and Jonah and the Whale. These were among the few Bible stories that featured wild animals, rather than boring barnyard animals like sheep and goats. Sunday school handouts and children’s Bibles showed the parade of animals peacefully lining up to enter the ark. Curiously, people always seem to illustrate this story mainly with animals from Africa, rather than Mesopotamia, where Noah is usually thought to have lived.

Noah's Ark plate

Happy animals on the Ark.

For example, when my son was born, Mom gave us a set of Noah’s ark bowls and plates, which have been favorites of all our kids. This Ark has mostly African animals: a pair of giraffes looking out of the upper windows, a pair of African elephants, a pair of zebras, and a green bird that could plausibly be interpreted as an African green pigeon. Animals that could have lived in Mesopotamia include a bear, a pair of cats that seem meant to be leopards (or lynxes), two rabbits, a squirrel, and a pair of white geese. A pair of raccoons have also wandered in from North America.

Of course, if the Flood was global, than animals from all over the world should be there, but the African focus is interesting to me. Maybe Noah really lived at the foot of Mount Kilimanjaro, rather than Mount Ararat?

Growing up, Mom took us to church almost every Sunday. Dad came along to church twice each year, on Christmas and Easter, but otherwise spent Sunday mornings working on electronics in the basement or fixing things around the house. At our church near the corn and soybean fields at the edge of town, we sat in long wooden pews. Mom sang alto on the old Lutheran hymns, which the congregation sang in four-part harmony, accompanied by an electronic organ, which filled the sanctuary with magnificent sound. Pastor stood at the front of the church in his white robe, leading  the Psalms and liturgy in a clear high tenor, solemn melodies in strange minor modes. From Pastor’s sermons, I gained the impression that Martin Luther (or was it Martin Luther King?) had nailed his 95 theses to the door of our very church, which puzzled me greatly, as the door of our church was glass.

I grew up reading both the Bible and dinosaur books, with no inkling that there was any conflict between these two sets of information. The Bible stories were presented as factual, not just in Sunday school, but everywhere. Network television presented Biblical epics like The Greatest Story Ever Told and Jesus of Nazareth in much the same way that they presented mini-series like Roots and Holocaust: fictionalized presentations of real events. Movies depicted efforts to find Noah’s Ark on Mt. Ararat as a reasonable quest, which (based on tantalizing clues!) may have already succeeded.

I remember standing on the screen porch as a kid, five or six years old, singing a Bible school song about it raining 40 days and nights for the Flood. When I noticed Mom was in the room I stopped singing, embarrassed at having been heard, but puzzling over the lyrics. I asked Mom how many days it rained for the Flood, and she said, “Well, like the song says, I suppose.” That’s what it said in the Bible, so it must be true.

I read the Old Testament and was fascinated by the lists of the begats. You could connect these ages up and come up with an age of the Earth! I was pleased when I came across a giant family Bible with the dates right in there, based on Bishop Ussher’s calculations. The date of Creation, 4004 B.C., was a bit troubling, since I knew from my dinosaur books that the world was much older than that.

As I got older, I started noticing more and more the contrasts between different ways of looking at the world. Pastor one day mentioned in a sermon, “I will never understand how you can put green grass in a brown cow and get white milk.” He meant this as an illustration of the miraculous ways of the Creator. But this seemed to me an easy problem. Grass is green because it has chlorophyll. There’s no chlorophyll on the surface of cows, or in milk, so of course they’re not green. And cows are brown (or whatever other color) because of the pigments in their hairs. Why is milk white? I wasn’t sure at the time (maybe because of suspended fats?) but this seemed an answerable question to me, not a mystery.

I must have been in about sixth grade when I began to lose faith in the Ark. I was drawing a picture of it, and wanted to draw it to scale. I checked Genesis for the dimensions, and started thinking about how much room all the world’s animals would really need. That was the first time I remember doubting that the Ark really could have held all those animals. Tugging at that thread threatened to unravel the entire tapestry.

In Junior High, I attended confirmation class, and participated more actively in church, for varied reasons, including a growing obsession with the fantasy world of Dungeons and Dragons. My friend Tim and I were in the same confirmation class, and we often volunteered to serve as acolytes, which meant we got to wear medieval red robes and play with fire, lighting and extinguishing candles with the long-handled candle-lighter, which was satisfyingly like a medieval weapon.

Tim and I also attended Prayer Share meetings, where I had my first encounter with Young Earth Creationism. Our friend Amy, who went to a different church, insisted that before Noah’s flood, it didn’t rain. This was based on a passage in Genesis stating that Eden was watered with a mist. I argued with her that this couldn’t be. If a mist came and watered the land,  then the water would evaporate, form clouds, and it would rain. There’s nothing miraculous about rain; it just happens.  And yet Amy insisted that, based on this text, there was no rain before the Flood.

I was mystified by this sort of argument, yet as I learned on moving to Indiana, where Young Earth Creationists are thicker on the ground, this is a typical line of Creationist argument. And while I find the slipshod use of science in these arguments maddening, I have a certain amount of sympathy for Biblical literalists. They take the Bible seriously, and make an effort to follow through with the implications of that. If  the Bible is the Word of God, and every line is true, then Noah must have really lived and done all the things that the Bible says he did.

The Ark Encounter is the logical next step from the Creation Museum. If Darwin is a problem for your religion, then so are his predecessors, the geologists whose findings inspired him. In 1830, nearly thirty years before Darwin published the Origin of Species, Charles Lyell published his Principles of Geology, which persuasively argued that geological features are the result of natural processes acting locally over many years, rather than the outcome of a single global flood. Darwin carried the first volume of Lyell’s with him when he sailed around the world on the Beagle. When Lyell published the second volume of his book, Darwin eagerly picked it up in South America, where he collected fossils, examined geological formations, and shot lots of birds. These volumes profoundly affected Darwin’s views, describing a world where natural processes acting gradually over many millions of years create the features of the earth’s surface: mountains, hills, layered beds of sedimentary rock, uplifted and faulted and infiltrated by magma.

Lyell was a devout Christian, but he argued vigorously against using the Bible as a science book. Instead, he argued we should look to the Earth itself for evidence of the Earth’s history. Lyell’s arguments proved persuasive, leading the the founding of geology as a proper science, one which is central to an industrial civilization that is deeply dependent on good guidance for where to look for things in the ground that we need, such as iron, coal and oil.

Even though the last serious scientific debates about Flood Geology ended nearly two centuries ago, I can’t help myself from dwelling on other scientific implications of the Noah story. What would it take to make a world wide flood possible, for example? And what biological evidence would we see if such a flood had happened?

Maybe this comes from having a father who is an engineer. Growing up, conversations with Dad often ended up with him sketching diagrams on scraps of paper, working out calculations in scientific notation. So I find myself doing similar things, such trying to calculate just how much water would be needed for the Flood.

According to Genesis, the Flood covered the highest mountains. The highest mountain on the earth, Mount Everest, is 8.84 km high. The radius of the Earth is about 6,378 km. To calculate how much water you would need to cover the whole planet to the top of Everest, you just need to calculate two spheres: the volume of the Earth ((4/3)πr3 = (4/3)π(6,378)3=1.087 x 1012 km3), and the volume of a sphere of Earth plus Everest ((4/3)π(6,387) 3=1.091 x 1012 km3). Subtract the volume of the Earth from the volume of Earth plus Everest and you get about 4.5 x 109 km3.

Each cubic km has a million cubic meters, each of which weighs about 1,000 kg, so multiply the volume by a thousand million (109) and you get the total mass = 4.5 x 1021 kg. That’s a lot of water. Scientists estimate that the total mass of all water on the Earth’s surface today is 1.4 x 1021 kg. So Noah’s flood would require over 3 times as much water to be added to the Earth’s surface as is currently contained in all the world’s oceans, rivers and lakes. Where did all that water come from? And when the flood was over, where did it go?

The deeper you dig with this story, the more problems you find. For example, one of the clear predictions from the Noah story is that every population of large animals on the planet should show evidence of having passed through a very tight genetic bottleneck some 4,000 years ago. Human beings were reduced to a population of eight (Noah, his wife, their three sons, and their sons’ wives). Most other animals (except for the edible ones) had a surviving population of just two.

Every man on the planet therefore should be a direct descendant of Noah. Every man should therefore have a Y-chromosome that is nearly identical to Noah’s. Given Bishop Ussher’s timeline, the Great Flood occurred in 2,348 B.C., or some 4,362 years ago. If we assume human generation times of 25 years on average between the births of surviving females, then some 174.5 generations have passed since Noah.

(25 years is a bit conservative; the average time between mothers and daughters in a population of Polar Eskimos was 27 years, and 32 years between fathers and sons (Matsumura & Forster 2008)).

A recent study of mutation rate on the Y-chromosome examined men in China who descended from a common ancestor 13 generations ago (Xue et al., 2009). They found 4 differences between the Y-chromosomes of these men, and estimated the overall mutation rate to be 3 x 10-8 mutations per nucleotide per generation. There are about 1.02 x 107 nucleotides in the part of the Y-chromosome that they examined. The average man’s Y-chromosome should therefore differ from Noah’s by about (3 x 10-8 mutations per nucleotide per generation) (174.5 generations)(1.02 x 107 nucleotides) = 53 mutations. Which, out of 10 million nucleotides, isn’t very many. So most men on the planet should have a  Y-chromosome that is nearly identical to Noah’s. But geneticists find far more differences than this. One recent estimate of when the last common ancestor of all human Y-chromosomes (“genetic Adam”) lived yielded a date of 120,000 to 156,000 years ago. This is a lot older than 4,000 years.

And that’s just humans. For the Noah story to be true, every single animal lineage on the planet would have to show evidence of a catastrophically severe population bottleneck in recent history. And of course we see no such evidence.

Another testable prediction of the Noah story relates to biogeography. If the entire planet were populated by animals that Noah saved on the Ark, then we would expect to see some very striking patterns, based on the dispersal ability of animals. Suppose, as the tradition holds, that Noah’s Ark landed on or near Mt. Ararat in Armenia. Armenia should therefore be the center of global biodiversity. The rest of the world would be populated by animals gradually making their way from Armenia to the rest of the world over the past 4,000 years or so. Some animals, like many bats and birds, would be able to fly long distances and cross rivers and seas. We might therefore expect to see bats and birds worldwide. Other animals, such as many large land mammals, can walk long distances, but cannot cross major barriers such as rivers, seas, deserts, and large mountain chains. Consider elephants, for example. They can travel long distances, and we would expect them to travel far across Eurasia and across the Sinai Peninsula to Africa. Even elephants, though, might having trouble crossing the  Sahara, in which case the current abundance of elephants in sub-Saharan Africa poses a puzzle.

But that’s a small puzzle compared to the presence of large land mammals on any land mass not directly connected to Eurasia and Africa. That includes Indonesia, New Guinea, Australia, and the Americas. Bison, wolves, pumas, deer, llamas, and jaguars should be common in the area around Armenia, but they would never reach the Americas.

Many animals, especially smaller animals, and many plants, cannot disperse very far at all. Consider the sloth. Sloths, as their name implies, move slowly. They spend most of their time hanging from trees, eating and digesting leaves. Try to imagine Mr. and Mrs. three-toed sloth leaving the Ark, exploring the post-flood world of mud and dead trees. What would they eat? How would they travel? How would they ever get from Armenia to Central and South America?

As Darwin discovered on his worldwide voyage on the Beagle, the distribution of animal and plant species around the world only makes sense in light of evolution. Sloths live in South America because their ancestors evolved there many millions of years ago. In the glory days of the Giant Ground Sloths, sloths dispersed out of South America well into North America, but sloths have never spread beyond the Americas.

One could go on and on. It’s shooting fish in a barrel, really, or beating a dead horse, or whatever metaphor of futility you prefer. There are many pages of the Internet devoted to detailing these problems in mind-numbing detail, such as here, and here. This is all really overkill, since the Noah story is clearly just that: a story. And it’s a story that would make sense for a people whose history is entwined with the great river civilizations of Egypt and Mesopotamia, the land between the rivers. The discovery of a flood story in the Epic of Gilgamesh suggests that the Noah story is a close retelling of that older story (or a retelling of a common ancestor of the two tales).

And yet, the Noah story still has enormous broad appeal. Why is this so?

Leaving aside the scientific problems, the Noah story raises all sorts of questions about God. Why would an all-powerful deity do such a bad job of making people that he has to wipe them all out and start again? Was everyone on the planet entirely wicked except for Noah’s family? Surely there would have been some innocent people among the masses of the wicked: young children, if nobody else. If God was unhappy with some men, why didn’t he just zap them? Later in the Bible God repeatedly demonstrates His selective zapping ability: striking Onan dead, for example, or the first-born sons of the Egyptians but not Hebrews. Killing everyone on the planet seems deeply unfair, unworthy of a just God.

So given all this, why does this story still hold such appeal?

As a kid, I suppose I liked the story because it had animals. Noah is a kindly old zoo keeper. What a cool job he has! Looking after all those interesting animals! I’d like to have a boat full of tigers and gorillas. And it’s an adventure story: Noah and his family taking care of all those animals on a boat during a flood.

One thing I liked about Aronofsky’s Noah was that it brought out something hidden in the Sunday school version of the story: this is a horror story. It’s about death and destruction on a massive scale.

The Sunday school Noah is a righteous man, a skilled carpenter who does what God tells him to, looks after his family, and saves the animals. He is a hero of conservation biology. But Aronofsky brings out much that is deeply disturbing in Noah’s story. What kind of man would shut out the world from the Ark, saving his immediate family and some animals, but nobody else?

Peter Chatterway argues that here Aronofsky is following a long tradition in Jewish commentary. For example, Rabbi Shmuley Boteach argues that Noah is a deeply flawed figure:

Noah is not a hero in Jewish lore. The Bible says that Noah was a righteous man “in his generation.” He was only a righteous man compared to the others who were far worse than he.

Now, why wasn’t he righteous? Because righteousness is all about what you do for your fellow man. And Noah does NOTHING for his fellow man. He doesn’t care, he has no compassion. He executes God’s commandment to the letter. So when God says “I’m going to kill everybody,” Noah says, “will you save my skin? Oh, I get an Ark? Okay, fine.”

[Noah] failed in the greatest mission of all. He failed to protect human life. And failed to fight with God when he wanted to take human life. He refuses to wrestle with God. Noah is a fundamentalist. He’s a religious extremist. God says “everyone will die” and Noah says nothing. But this is not what God wants. God wants people with moxie! God wants people with spiritual audacity! He does not want the obedient man of belief. He wants the defiant man of faith.

It isn’t until Abraham, when God says “we have the rainbow and I promise not to destroy everyone, but I will destroy these two cities Sodom and Gomorah,” Abraham does something audacious. He says “will the judge of the entire Earth not practice justice?” He lifts his fists to heaven! He raises a cudgel to Heaven! This made him the first Jew. A Jew does not just accept a divine decree, he does not just bow his head in silent obedience.

The word “Islam” means “obedience before God” or “submission before God.” Soren Kierkegaard the great Danish theologian sums up Christianity as being a “leap of faith.”

Judaism has no leap of faith. “Israel” means “he who wrestles with God.” You see none of that in Noah. Neither in the Torah or in this film, so in that regard, this movie portrays this very well. No other religion does this, they would see this as heresy. It’s amazing, it’s breathtaking!

The scientific debate about Noah’s Flood ended nearly two centuries ago, with the birth of modern geology.  What we have learned since then about the deep history of the Earth is much more interesting and satisfying than the old myths. And yet, the myths still have a hold on our imagination. This may not be a bad thing. The Noah story can help promote an appreciation for our responsibility to life on earth: we must be good stewards of our planet. At the same time, understanding Noah to be a flawed man, a failure in his unquestioning obedience, might help make us better human beings.

 

References:

Matsumura, S. and P. Forster (2008). “Generation time and effective population size in Polar Eskimos.” Proceedings of the Royal Society B-Biological Sciences 275(1642): 1501-1508.

Xue, Y. L., Q. J. Wang, Q. Long, B. L. Ng, H. Swerdlow, J. Burton, C. Skuce, R. Taylor, Z. Abdellah, Y. L. Zhao, Asan, D. G. MacArthur, M. A. Quail, N. P. Carter, H. M. Yang and C. Tyler-Smith (2009). “Human Y Chromosome Base-Substitution Mutation Rate Measured by Direct Sequencing in a Deep-Rooting Pedigree.” Current Biology 19(17): 1453-1457.

Eagle flying past nest on Lake Vermillion, MN.

Family Ties

Anton Johnson was born to a family of farmers in  Ärtemark Parish, Sweden in 1859. With his wife Christina he homesteaded a plot of forested land east of Ely, Minnesota. As I think Garrison Keillor has said of other Scandinavian migrants, they left their homeland, with its dark forests, thin rocky soil, cold weather, and short growing seasons, to find a better country. They traveled thousands of miles across the ocean and halfway across America until they reached Minnesota, where they settled down because it reminded them of home: dark forests, thin rocky soil, cold weather, and short growing seasons.

As it turns out, though, Anton got a job working underground in an iron mine, so it didn’t matter so much that the soils were poor and the weather was cold. This was in the early days of Ely’s rapid growth as a mining boom town. He and Christina had one child, Burt, born in 1890. Just over a year later, while Anton was working in the mine, a massive rock fell on his head and killed him. He was not quite 33 years old.

Christina remarried. Burt grew up, married a Norwegian girl, and had two daughters, who had their own families, whose members dispersed across the continent. I knew Burt as Dadda, my great-grandfather: a thin, straight, dignified old man, with thin white hair, thick, black, arched eyebrows, large ears and a long, thin face, serious but kind.

This August, nearly two dozen of his descendants and their families gathered together for a family reunion in a  cabin in the woods in northern Minnesota. In this group, there are some striking family resemblances. Some of my cousins look so much like their mothers that looking at them I feel I’ve become unstuck in time. There are many things that bind us together as a family, including shared memories of gathering in the north woods from time to time over the years. But I am also struck by how different we all are. We are family, but each person is a distinct individual, with different hopes and dreams, likes and dislikes, quirks and foibles. This is obvious, of course, even among siblings; each baby has its own temperament, and grows up to be a unique person.

Uncle Tim now lives out west, but owns the land that Anton and Christina homesteaded. One day we drove to the Ely area and spent two hours searching the woods for the property. Walking through the woods, slapping mosquitoes and gathering raspberries, it was easy to imagine what it must have looked like when those settlers first arrived.

The winters are cold and long. Grandma talked about how winter lasted seven months. I’ve been ice fishing up there in late April. Then once it warms up in the summer there are the mosquitoes, ticks and leeches. As soon as it gets warm enough to bare any skin there’s a crowd of bloodsuckers waiting to take a bite out of you. But the forests grow a bounty of raspberries and blueberries, and the lakes are full of fish. Loons cry their haunting call on the lakes, eagles fly overhead, and in the forests deer, wolves and bears are abundant.

Those northern Minnesota lakes and woods are almost enough to make me believe in ghosts. They vividly bring to mind memories of people who have passed on: sitting with Dadda at his breakfast nook while he explained the town of Virginia’s residential steam heating system; Nana lying in the nursing home bed with her bright blue eyes and wispy white hair;  Poppa scaling a bass after a long day fishing together; Mom orchestrating everyone in previous reunions, making sure that everyone was included and recognized and fed; and Grandma doing the hokey-pokey. I feel a connection to the land and the people. I can’t help wondering, though: if I stumbled back in time and met Anton and Christina in those woods, would we have much in common? Would we recognize each other as kin?

Kinship and lineage are powerful themes in the stories we tell. For example, in Dan Brown’s The Da Vinci Code, a central premise is that Jesus and Mary Magdalene had a child, thereby founding a lineage that continues unbroken to the present. Supposing for the moment that this were true, would people in this lineage be particularly special? Would they be more Christ-like (or Magdalene-like) than the average person?

From a religious point of view, this might be considered a silly question, of course; those who believe in the divinity of Jesus generally attribute this to Jesus having an extraordinary spirit in an ordinary human body. But in the fictional world of the Da Vinci Code, people devoted their lives to the principle that the lineage of Jesus was extra special, worthy of protection (or persecution). And even within the religious tradition, the writers of the Bible show great interest in lineages, describing in detail the generations connecting Jesus to the line of David, Abraham and Adam.

As an exercise focusing just on genetics and not spiritual matters, how many genes would a modern-day member of this lineage have in common with Jesus (or Mary)? We can estimate this using the coefficient of relatedness, r, defined as the probability that any two individuals share a given gene by common descent. (Most genes that we have are very similar to those of every other person on the planet, differing only in minor details, if at all, but the chance that any two genes are identical by descent is estimated by r.) Each sperm or egg that a person produces contains half of that person’s genome. Therefore each generation results in a halving of genetic relatedness: my daughter has half of my genes (r=0.5), and if she has a daughter, that child will have one fourth of my genes (r=0.25).

Estimating r for lots (n) of generations, assuming no inbreeding, r=1/(2n). Assuming human generation time to be about 25 years, about 80 generations have passed since the time of Jesus. The coefficient of relatedness between Jesus and any living descendants of his would thus be 1 over 1.2X1024, which is a really huge number – on the order of the total number of stars in the observable universe. One divided by such a huge number is effectively zero. The coefficient of relatedness between Jesus or Mary and any living descendant of theirs therefore would be r=0.0000000 (with zeros going on and on and on).

Of course, this is assuming that no inbreeding occurred. If (as is common in royal lineages) efforts were made to ensure marriages among members of the lineage, such as cousins, then r would be higher. But even so, with even a modest amount of marrying outside the lineage, the disruptive effects of sexual reproduction would rapidly erode much of the genetic similarity between the founders of the lineage and their remote descendants. Insofar as anything special about Jesus or Mary Magdalene was contained in the particular combinations of their genes, after a few generations of mixing and matching genes with people from other lineages, the descendants would have no more in common with Jesus or Mary than most other people in that population.

The same goes for any lineage. The “royal blood” of Queen Victoria, for example, is seven generations removed from the youngest heir to the throne, Prince George (r=1/27=0.0078). Thus, from a genetic point of view, Prince George is not particularly similar to Queen Victoria, despite being a relatively recent direct descendant of hers.

This calculation of r, though, doesn’t work for all genes. Some genes are passed down in packages rather than individually. We inherit our mitochondrial genome intact from our mothers. Mitochondrial genomes thus change only slowly, through the accumulation of mutations. In the same way, boys inherit their Y-chromosomes intact from their fathers. Prince George thus has the same Y-chromosome as his paternal grandfather Prince Charles.

Back in 2003, Tatiana Zerjal and colleagues published a paper showing that some 8% of men in Central Asia shared nearly identical versions of the Y-chromosome (Zerjal et al., 2003). Based on mutation rates and geographic patterns, they estimated that the family tree of this lineage originated in Mongolia roughly ~1,000 years ago. The most likely explanation of the wide spread of this chromosome was thus the historically well-attested reproductive success of Genghis Khan and his descendants.

There’s not very much on the Y-chromosome, though; just over 200 genes. Just because a man happens to have inherited a slightly mutated version of Genghis Khan’s Y-chromosome doesn’t mean that he shares anything more in common with Genghis Khan’s personality than any other man on the planet.

Personality and appearance both have strong genetic components, but because of sexual reproduction, similarities between lineage founders and descendants rapidly erode over time. So one might ask: given this erosion in similarity across the generations, why do we care so much about kinship and lineages? And more specifically, if there are only 200 or so functional genes on the Y-chromosome, why do patriarchs invest so much effort in ensuring that their particular Y-chromosome is perpetuated?

I suppose a major part of the answer must be that lineage survival is a pretty good proxy of fitness. If organisms are designed by natural selection to do whatever they can to promote the survival of their lineage, such organisms will leave more descendants, and thus more copies of their genes, than organisms that are indifferent to their lineage. If your lineage goes extinct, you won’t leave any copies of genes in the population. But if your lineage survives for two or three generations, and the number of individuals per generation grows rather than declines, then your genes have a good chance of surviving far into the future. Thus the particular satisfaction and happiness that grandparents and great-grandparents experience in seeing their descendants makes good evolutionary sense.

As for patriarchs, the focus on the patriline is less to do with the Y-chromosome itself, but with the greater potential variance in reproductive success between the sexes. The reproductive success of female mammals is limited by the number of babies they can have, whereas the reproductive success of male mammals is limited by their mating success. A Genghis Kahn or King David thus can have many more offspring than a Börte or Bathsheba.

Anton Johnson had just the one wife, though, rather than a harem, and he had only a single child before his life was cut short by a falling rock. Nonetheless, his lineage has carried on and grown.

The particular combinations of genes that Anton and Christina carried, though, have long since been mixed up with the genes of other lineages from varied parts of the world. That is, of course, the whole point of sexual reproduction. But whether due to genes, family experience, mate choice, or just the basic heritage of humanity, many members of this family do share an enjoyment in being outdoors, tramping around in the woods, and looking at living things.

White pine on Anton and Christina's homestead.

White pine on Anton and Christina’s homestead.

As we searched the woods, my son was the first to find the pipe in the ground that marked the southeast corner of the land that Anton and Christina homesteaded. After finding the corner marking, we could discern a cut line along the eastern boundary of the property: a straight path devoid of trees, brambled over in raspberries. Off the property, much of the land has been logged and is now covered with secondary growth: white-barked birches and poplar, thin trees crowded together, straining for the sky. But the family land has older growth, including a grand old white pine that already must have been a tall tree a century ago.

I don’t know what Anton Johnson was like as a person. If I could wander back to this same land 130 years ago, would I recognize any more kinship with him than with any of the other immigrant miners in the area? All the same, I still very much like the thought of him walking in the shadow of that same white pine, and perhaps admiring the flight of an eagle passing overhead.

 

Zerjal, T., Y. Xue, G. Bertorelle, R. S. Wells, W. Bao, S. Zhu, R. Qamar, Q. Ayub, A. Mohyuddin, S. Fu, P. Li, N. Yuldasheva, R. Ruzibakiev, J. Xu, Q. Shu, R. Du, H. Yang, M. E. Hurles, E. Robinson, T. Gerelsaikhan, B. Dashnyam, S. Q. Mehdi and C. Tyler-Smith (2003). “The genetic legacy of the Mongols.” American Journal of Human Genetics 72: 717-721.

http://www.wired.com/2008/04/grand-theft-aut-9/

Video Games

Do playing violent video games and watching violent television shows make people act violently? That was one of many questions discussed at the XXIst World Meeting of the International Society for Research on Aggression (ISRA), which met this July in Atlanta, Georgia.

ISRA was founded in 1972, “In the shadow of the Cold War, the Vietnam War, and social unrest throughout the United States.” Since that beginning, a goal of the society has been to use research to find ways to “reduce harmful aggression.” This is a goal that I share. But during the course of the meetings, I couldn’t help but wonder: after all these years of research, what have aggression researchers learned that has been of practical use to help people reduce harmful aggression in the real world?

Some of the ISRA talks focused on the neurobiology of aggression. This is a scientifically important topic, definitely worth pursuing. But I suppose that the practical benefits of such research are largely limited to a fairly narrow range of specific circumstances, such as developing drugs to help reduce violent behavior in people with certain mental illnesses. Will a better understanding of neurobiology really help to reduce rates of warfare, or civil strife, or violent crime?

Many of the other talks and posters focused on the social psychology of aggression. A particularly popular topic was the effect of violent media on aggressive behavior. The most prominent of these was the John Paul Scott Award talk by Professor Rowell Huesmann. This award “recognizes a lifetime or substantial contribution to aggression research,” so this is clearly a topic close to the heart of the society.

Professor Huesmann spoke on aggression and the media. He described aggression as a contagious disease, which is contracted through exposure to violence, whether real or fictional. Watching violence on television, or playing violent video games, gives children “scripts” about how they should act. Because people imitate, they imitate the violence they see on TV and experience in videogames and act aggressively in real life.

Professor Huesmann is an esteemed scholar with a long list of publications, honors and grants. His findings are based on studies with large sample sizes and careful statistics that show consistent, positive correlations between exposure to violent media and violent real life behavior. He also seemed like a very nice guy, earnestly devoted to reducing problems of violence in the real world.

Despite all this, I think the Media Violence Hypothesis doesn’t explain a great deal of violent behavior, even though it is intuitively appealing on several levels.

The argument that exposure to media violence causes real world violence has a certain plausibility to it. Kids imitate things they see on TV. In my high school, certain guys were constantly imitating pro wrestling moves with their buddies (though they always did so in comic slow motion). Teachers tell me they see their kids imitating moves they see on TV, such as Teenage Mutant Ninja Turtle attacks.

Another appealing part of the argument is that as video games become increasingly realistic, the violence becomes increasingly graphic and disturbing. Back in the 1990s, I played a game on a friend’s computer that must have been some version of Wolfenstein — a first person shooter that involved walking around a castle and shooting at Nazis. After playing for a while, I found the whole first person shooter aspect rather disturbing, particularly the blood pouring from the bullet wounds of the dead computer Nazis. I wouldn’t want my kids playing this game, and can imagine how spending many hours playing such games might affect a person.

So I can see how the Violent Media Hypothesis is appealing, especially to parents and educators. This hypothesis also suggests an obvious intervention: increased control over the media. If the hypothesis is true, then limiting violence in the media should provide strong practical benefits for reducing rates of violence in the real world — though of course this raises all sorts of problems for anyone interested in protecting First Amendment rights.

Despite the intuitive appeal of the hypothesis, though, and quite apart from concerns about media censorship, there are a number of reasons to think that that Media Violence Hypothesis doesn’t really hold up.

First of all, exposure to violent media isn’t a necessary precursor to violence. Neither ants nor chimpanzees nor any other animals require exposure to violent media to commit acts of violence. Numerous acts of violence occurred in human history, and prehistory, long before the invention of Pac-Man and Space Invaders.

This is, admittedly, a weak objection, given that the argument isn’t just about the media; it’s about the violence depicted in the media. Movies, TV and video games just provide novel means of displaying violence; new ways of spreading the contagion of violence. Long before violent media existed, people saw acts of violence being committed, which according to this hypothesis, would have resulted in further imitative acts of violence, which in turn would spawn yet more acts of violence.

There are, however, other reasons to think this hypothesis is implausible. One of these is my own personal experience. I don’t particularly seek out violent media. I have never played Grand Theft Auto or similar video games, and I don’t seek out slasher films. All the same, over a lifetime of watching TV and movies, and playing various kinds of games, I have been exposed to an enormous amount of simulated violence: murder, mayhem, rape, pillaging, decapitation, dismemberment, and all manner of horrible things. I’ve watched the entire population of the planet of Alderaan being destroyed by the Death Star. As a teenager playing Dungeons and Dragons, I fought countless virtual battles, throwing spears and whiskey bombs at orcs, hobgoblins and various other enemies. Playing Risk, I have commanded armies that slew many thousands of soldiers (though these were represented in the innocuous, non-bloody form of Roman numerals). I watched all six seasons of the Sopranos, in which many horrible murders were graphically depicted.

One would think that, according to the Media Violence Hypothesis, I would be deeply infected with the contagion of violence, and would have acted out these violent scripts repeatedly in my life. And yet, I have enjoyed a quite peaceful existence,  apart from a few rough wrestling bouts and fist fights in grade school.

I don’t think I’m unusual in this respect. Lots of people watch lots of violence on TV and movies, and experience simulated violence in video games, fantasy role playing games, and other forms, and yet have never committed a single act of violence.

Given all this, it would seem that violent media are neither necessary nor sufficient for violence to occur. Nor does it explain one of the most consistent findings in aggressive studies: men are consistently more violent than women. Men commit the great majority of homicides, and commit far more atrocities of war than women. If both sexes are routinely exposed to the same violent media, why should men be more violent than women?

Additionally, the Violent Media Hypothesis doesn’t  fit with patterns of violence over time, or across geographic space.

As Manuel Eisner described in his excellent plenary talk, rates of homicide have declined over the past thousand years or so in Europe. If the Media Violence Hypothesis were correct, we should see an enormous increase in violence following the invention and widespread dissemination of movies, television, and video games in the 20th Century. But what we see instead is a marked decrease in many different kinds of violence, including warfare and homicide. The horrors of WWI occurred when the film industry was still in its infancy. Television barely existed at the start of WWII. Since these cataclysmic events, the 20th Century has seen a steady decline in per capita rates of death from war, and decreases in homicide rates across Europe and North America. According to Eisner, there was an uptick in homicide in the 1960s through the early 1990s, but homicide rates declined thereafter, despite the release of a series of increasingly violent video games. (Grand Theft Auto, for example, was first released in 1997, when homicide rates in the US were on their way down.)

Considering geography, one would predict that the parts of the world most plagued by violence would be those most intensively saturated by television, films, internet and video games, such as the United States, Europe, and Japan. But while the US has higher rates of violence than Europe and Japan, its homicide rates are far below those of many countries where access to violent media is much more restricted. In many war-torn countries of Africa and the Middle East, per capita incomes are much lower and many people lack electricity, much less Xboxes.

So on a broad scale, the data don’t seem to support the Media Violence Hypothesis. It cannot explain why the latter half of the 20th Century was more peaceful than the first half, or why Japan is more peaceful than, say, Afghanistan.

The hypothesis seems even more doubtful from a theoretical perspective, especially when considered from an evolutionary perspective. In particular, why should evolution design people, or any other organism, to imitate acts of violence?

In evolutionary game theory, violence is a strategy that animals use to obtain key resources for survival and reproduction. If I am attacked by a predator, or a hostile member of my own species, I will fight back. Male chimpanzees fight for status, and for opportunities to mate with fertile females, and to defend and expand their territory.

Under many circumstances, imitating violent behavior would be maladaptive. For example, in chimpanzee societies, the alpha male frequently conducts charge displays, charging at, chasing, and sometimes hitting other community members. If a young, low-ranking male started imitating the alpha male by charging around and attacking other chimpanzees, he would get beat up in a hurry.

Professor Huesmann described studies showing that both Palestinian and Israeli children exposed to more media violence were more aggressive. Fair enough. But does anyone really think that the ongoing conflict between Israelis and Palestinians is the result of too much violent television? Or that Russia’s invasion of Crimea and ongoing support for separatists in Eastern Ukraine is the result of, say, Vladimir Putin watching too many Steven Seagal movies?

I would like to think that research on aggression can, and should, contribute to reducing harmful aggression. But I think that to find practical and effective solutions, we need to focus on the right level of analysis, guided by theoretically plausible hypotheses. Evolutionary theory provides critically important guidelines for what sorts of hypotheses are likely to be plausible. But a complete understanding of violent behavior also needs to look at a broad range of factors, including history, politics, and demography. A few disturbed people may be inspired to violent acts by violent video games, but it seems likely that the great majority of violent acts are best explained by conflicts over limited resources,  such as land, oil, and status.

http://gamemoir.files.wordpress.com/2014/02/stephen-colbert-on-video-game-violence.jpg

http://gamemoir.files.wordpress.com/2014/02/stephen-colbert-on-video-game-violence.jpg

 

 

 

 

 

 

 

 

 

Caesar in war paint

Planet of the Apes

28 July 2014

The latest Planet of the Apes movie raises interesting many interesting questions, such as: what would it take for other apes to replace humans as the planet’s ruling primates?

Spoiler Alert: if you haven’t seen the movie yet, you might not want to read any further until you have. I try to steer clear of plot details, but if you’re the kind of person who likes to know as little as possible about a movie before seeing it, consider yourself warned.

I grew up watching the original Planet of the Apes movies. I am sure seeing movies of a world ruled by apes fueled my interest in our hairy cousins. It was a rich time for anyone interested in apes. The first movie came out in 1968, the same year that the site where Jane Goodall studied chimpanzees, Gombe, was upgraded from a game reserve to a National Park. We watched films of Jane Goodall and the chimpanzees of Gombe in elementary school. New discoveries about the apes were reported regularly in the glossy pages of National Geographic. Studies of sign-language using apes like Washoe and Koko suggested apes were on the brink of human intelligence. Movies like King Kong and the Planet of the Apes franchise presented apes as both dangerous and fascinating, blurring the boundary between human and animal.

I had a special interest this latest Planet of the Apes movie as I contributed some recordings of chimpanzee vocalizations. As a result my name shows up on the big screen for a few seconds, after Ape Extras but before Editorial Assistant, New Orleans. The Chicago Sun-Times even noticed.

(The name  Michael Wilson also shows up in the credits for the original movie, as writer of the screenplay  — though that was of course somebody else!)

I thought they did a good job with ape vocalizations in the movie. One of my complaints in general about animals in movies is that they make much more noise than animals do in real life. Movie predators, whether lions or dinosaurs, always seem to roar right before attacking their prey – something real predators would never do, as they seek to catch their prey by surprise. Roars are for warning members of your own species to stay away (and/or for attracting mates), not for chasing away your prey!

Chimpanzees can be extremely noisy, but most of the time they are very quiet. So one of my recommendations to the sound editors was to avoid extraneous calls. I was very pleased to see that for many scenes, the apes were indeed fairly quiet.

And when the apes did vocalize, I enjoyed hearing real ape calls, and different calls for each species.  I particularly liked one scene where the apes give a massive round of pant-grunts to Caesar. This is a call that chimpanzees use to show submission, and they used it in the right context for this film.

I liked that the apes mainly used sign language, and that when they did speak, they had rough, breathy voices, much like Viki the chimpanzee did when being trained to say words like “cup” and “up.”

In general, I thought the film did an excellent job building the characters and story. The main ape and human characters are complex, with understandable motives, and aren’t depicted as being either simply good or evil.

I think this might be the best movie yet in the franchise, and well worth seeing.

As an ape ecologist, though, I can’t help thinking about certain things.

For example, Muir Woods seems like a pretty rotten place for apes to live. It has trees, sure, but they are mainly redwoods and other conifers that produce no ape-friendly food. Apes are specialists in ripe fruit, which is in pretty short supply in a redwood forest. According to the Muir Woods website:

“Life in a redwood forest is determined by the low light conditions that restrict growth of plant species producing flowers, nuts, or berries. In addition, coast redwood trees contain an abundance of tannin (or tannic acid), a chemical compound that deters the presence of insects. Taken together, these conditions create an environment that is relatively low in the resources that typically form the base of a food web.”

So while it’s really cool to see apes swinging from the branches of redwoods, that forest is pretty grim habitat for apes. The gorillas might be able to subsist on herbs growing in the understory, but these are largely ferns and not very palatable. The chimps and orangutans would be pretty hungry there. They might use the forest as a temporary refuge, but would quickly move on to more suitable habitat, such as the overgrown gardens and city parks of post-apocalyptic suburbs.

If ordinary chimpanzees, gorillas and orangutans were released into the California wilderness, they would probably go their separate ways. The orangutans would forage alone. The male gorillas would compete over the female gorillas, until each silverback had a small group of females for himself. Each gorilla group would then forage separately. The chimps might start off as a single community but over time they would probably fission into several mutually hostile communities, each defending their own territory. It’s not clear why these different ape species stick together, or why they live in a village instead of sleeping up in the trees like real apes do. But of course these are retrovirus-mutated, hyper-intelligent talking apes, so they behave differently.

The film is surprisingly conservative in depicting ape romantic relationships, in that Caesar at least seems to be in a monogamous marriage with Cornelia. I suppose showing Caesar as a loyal family man makes him more appealing to viewers. However, a normal alpha male chimpanzee would try to monopolize matings with all the fertile females; and these females would try to mate with multiple males, even against the wishes of the alpha male. But perhaps the mutating retrovirus also makes apes monogamous.

But a big question relates to the film’s fundamental premise: what would it take to destroy human civilization, and clear the way for the world to be ruled by another kind of ape? (Or, in this case, a triumvirate of three different ape species.)

As Ruben Bolling points out,the Rise of the Planet Ape is a true story, and we are living it: we are the apes that have taken over the whole planet. But is human domination of the planet inevitable? How hard would humanity have to be hit to make way for other apes?

In this movie, humans are very nearly wiped out by a genetically engineered retrovirus, ALZ-113,  that makes nonhuman apes super intelligent but kills humans. (This has interesting parallels with SIVcpz, a naturally occurring retrovirus, which was transmitted from chimpanzees to humans, probably by people hunting and butchering chimpanzees for food. When contracted by people, the virus is called HIV-1 and causes the disease AIDS, which has killed many millions of people around the world. SIVcpz doesn’t make apes super intelligent, of course, and we have learned that it is also fatal to chimpanzees (Keele et al., 2009)).

According to newscasts in the movie, almost everyone who contracts the virus dies; only 1 in 500 survive. Since the virus is highly contagious and transmitted by sneezing, this leads to a much more devastating result than even the AIDS pandemic.

There are about 7 billion people on the planet today. So if 1 in 500 people died, there would still be 14 million people on the planet. Such a rapid and catastrophic epidemic would have huge impacts on the survivors, though, as food distribution systems and everything else collapsed. Say only 1 in 10 of people who survived the virus would survive the aftermath of collapsing civilization. That would bring the total population of people on the planet down to 1.4 million (which is still four to five times the total number of chimpanzees living on the planet today). This is probably a low figure, given that many people on the planet are subsistence farmers and herders of livestock.  Many people living in rural Africa, for example, would be able to survive the collapse of industrialized civilization, because they mainly live off the land without access to electricity, plumbing or fossil fuels.

In the San Francisco Bay Area, though, most people have no idea how to farm, herd livestock, or live off the land. Collapse would hurt people hard. So starting from a Bay Area population of about 7.44 million, if 1 in 500 die from disease, that leaves around 14,880 survivors. If 90% of those survivors died from starvation and post-apocalyptic fighting and such, then only around 1,488 people would be left in the Bay Area. That seems in line with the number of people crowded into the refuge of San Francisco (though as my wife noticed, the virus seems to have selectively killed all the Asians).

(Though why are they living in the middle of the city? I would think any survivors would mainly live on isolated rural farmsteads, where they can grow their own food, rather than crowding into the city center. How do these people eat? But it does look cool and dystopian to have everyone crowded together in the post-apocalypse city — maybe more so than setting it, say, on the outskirts of post-apocalypse Fresno.)

(Some other quibbles: Ten years post-apocalypse, I’m not sure anyone would still have usable manufactured clothing, eyeglasses or electronics anymore.  Even in my own family, after a year living abroad, with easy access to clothing and other supplies, the clothes we brought with us are ragged, the kids need new eyeglasses, and my son and I both need new shoes. Life post-apocalypse would certainly be much harder on such supplies. Moreover, there would certainly be no birth control or antibiotics. Sexually active women would be pregnant or nursing — which would have huge impacts on society. Weirdly, almost no young  human children, or women with nursing babies, were shown in this film.)

ANYWAY…

Based on the number of apes living in Muir Woods, they must have been reproducing at a really high rate compared to normal apes. This wiki states that there are 2,000 apes living in the ape village. Now that’s a lot of apes. Currently there are only about 2,000 captive chimpanzees in the United States. The starting population in Muir Woods must have been a lot less than that, since they started with apes escaping from just two captive colonies, and it would be hard for apes from other parts of the country to find out about the Muir Woods population, much less travel there.

Is it realistic to have 2,000 apes in ape village just 10 years after the ape revolution?

One key to the success of humans is demography. We can reproduce much faster than other apes. For example, suppose by coincidence that both the surviving human population in San Francisco, and the chimpanzee population in Muir Woods, started out at about 1,000 individuals. (Gorillas reproduce more quickly than chimpanzees, and orangutans reproduce more slowly, but since in the movie most of the apes are chimps, I’ll focus on them.) In a best case scenario, chimpanzee populations could potentially grow at about 2% per year. (Most wild chimpanzee populations “grow” at about 0% per year, though, because mortality is high and food supplies are limited — which in turn limits fertility and growth.)

Projected populations of humans and chimpanzees post-apocalypse, starting from 1000 individuals in each population.

Projected populations of humans and chimpanzees post-apocalypse, starting from 1000 individuals in each population.

So starting out with 1,000 chimps, in ten years there would be only about 1,221 chimps (if they somehow found food and didn’t suffer high mortality from predation, warfare etc.). Human hunter-gatherers, though, can grow at much faster rates, such as around 4%, even without medical care and with all of the hardships that hunter-gatherers face. At this rate, starting with 1,000 humans, we’d have around 1,492 people by the end of ten years — so about 270 more humans than chimps. And realistically, survivors in California would be farmers, not hunter-gatherers, with potentially even faster population growth. So if Ape Village apes are reproducing like normal chimpanzees, and if the starting population was in the hundreds, a population of 2,000 ten years later is not realistic.

Why can human populations grow so much faster than chimpanzees?

In some ways it is surprising that this can even be possible. After all, humans take longer to reach maturity than chimpanzees. Female chimpanzees have their first birth around age 14 (males reach full size around age 16, but for population growth, it’s females that matter more). Humans hunter-gatherers take longer to mature, with an average age of first birth at 18-20 (Hill & Kaplan 1999). Moreover, even though humans live longer than chimpanzees, human females stop reproducing in their forties — so their reproductive careers are, on average, shorter than those of chimpanzees.

However, once humans do grow up, they can reproduce quickly.  Chimpanzees have an average interval of around 5 years (Jones et al., 2010), whereas hunter-gatherers have an interbirth interval of only 4 years (Hill & Kaplan 1999).

How can women reproduce more quickly than chimpanzees? A big part of the answer must be cooking. Thanks to fire, humans can extract more energy from the environment, by increasing the energy available from food, and by making otherwise unpalatable foods safe to eat (Wrangham et al., 1999). Cooking likely helps children grow faster, by providing soft, energy rich foods from a young age, whereas chimpanzee children continue drinking their mother’s milk for longer, as they gradually add tough, hard adult foods to their diet. This surely has a big impact on human fertility and growth rates.

In the movie, the apes in Ape Village had fires in each house, so maybe they were cooking? That would certainly help them reproduce more quickly.

Another reason human populations can grow so much faster than chimpanzee populations is that humans have much lower mortality than chimpanzees, even in hunter-gatherer populations without access to medicine. Hunter-gatherers regularly live into their 50s, whereas the median age of survival for wild chimpanzees is about 30, and few live into their 40s. What accounts for this difference?

I suspect cooking is probably important for reducing mortality as well.  Cooking and other food extraction and preparation technology likely help people obtain food even in difficult times of the year, whereas chimpanzees in seasonal environments may become weak and more likely to die from diseases. Cooking also must help people live longer by providing soft foods that they can continue to eat into old ages, as their teeth wear down.

So super-intelligent mutant apes potentially *could* take over the world, but only if most of the humans are killed off, and apes learn how to cook.

 

Works cited:

Jones, J. H., M. L. Wilson, C. M. Murray and A. E. Pusey (2010). “Phenotypic quality influences fertility in Gombe chimpanzees.” Journal of Animal Ecology 79(6): 1262-1269. get pdf

Keele, B. F., J. H. Jones, K. A. Terio, J. D. Estes, R. S. Rudicell, M. L. Wilson, Y. Li, G. H. Learn, T. M. Beasley, J. Schumacher-Stankey, E. E. Wroblewski, A. Mosser, J. Raphael, S. Kamenya, E. V. Lonsdorf, D. A. Travis, T. Mlengeya, M. J. Kinsel, J. G. Else, G. Silvestri, J. Goodall, P. M. Sharp, G. M. Shaw, A. Pusey, E. and B. H. Hahn (2009). “Increased mortality and AIDS-like immunopathology in wild chimpanzees infected with SIVcpz.” Nature 460: 515-519. get pdf

Hill, K. and H. Kaplan (1999). “Life history traits in humans: Theory and empirical studies.” Annual Review of Anthropology 28: 397-430. get pdf

Wrangham, R. W., J. H. Jones, G. Laden, D. Pilbeam and N. Conklin-Brittain (1999). “The raw and the stolen: cooking and the ecology of human origins.” Current Anthropology 40(5): 567-594. get pdf

 

 

 

 

 

Cousins Gossamer and Glamour at termite mound.
(11 June 2014)

Twins and Cousins

Gombe is a special site for many reasons. Among them: It is the first site where wild chimpanzees were observed to make and use tools. It is also the only wild site where twin chimpanzees have survived to adulthood. On my recent visit to Gombe, I had the good fortune to see the twins and their daughters making and using tools to fish for termites.

Back in 2002, I remember following a large group of chimps in the Kasekela community, on the narrow trail climbing the steep path above Kakombe Valley, heading south to Mkenke Valley. It was Mabungo season and the chimps were feasting on fruits from the different kinds of Mabungo vines, especially Mabungo Makubwa (Big Mabungo) and Mabungo Madogo (Little Mabungo). The chimps traveled single file down the narrow trail. In the midst of the rainy season, everything was lush, green, and wet. The last chimp in the line was Gremlin, carrying her twins, Golden and Glitter, on her back. Sometimes their older sister Gaia would help mom by carrying one of the little twins. Gaia’s help is probably one reason that Golden and Glitter survived to adulthood — the only known pair of wild chimp twins known to have done so. Even with this help, though, the twins slowed Gremlin down. Being new to Gombe, struggling with the hikes up and down the hills, I was quite happy walking behind them, grateful for a chance to rest a little while watching these little girls play.

Amri collecting data on the twins, Gitter and Golden, and their babies, Gossamer and Glamour.

Amri collecting data on the twins, Gitter and Golden, and their babies, Gossamer and Glamour.

Now Golden and Glitter are all grown up.  Female chimpanzees usually leave the group of their birth and join a new one, to avoid mating with their brothers, uncles, fathers and such. At Gombe, though, about half of the Kasekela females stay in their natal group, probably because the dispersal options are limited: Mitumba is small and crowded, while Kalande is big but less forested (so less food) and has too few adult males.  So Golden and Glitter have stayed in Kasekela, as did their mother Gremlin.

We don’t know if Gremlin’s mother Melissa was born in Kasekela or if she immigrated from elsewhere. But now that Golden and Glitter have babies of their own (Glamour and Gossamer), we have four generations of G-family girls in one community. Their older sister Gaia has also stayed in Kasekela. When all the G-family moms and babies get together, it’s more like a baboon matriline than a typical chimpanzee group of unrelated females. This concentration of female kin might have some interesting implications for social behavior. Maybe all these related females will gang up on other females to control access to the best home ranges? They do seem very well established in Kakombe Valley, the best, most productive valley in Gombe in terms of chimpanzee foods.

Glamour, who just like her mother Golden, has a white spot on the top of her head. (11 June 2014)

Glamour, who just like her mother Golden, has a white spot on the top of her head. (11 June 2014)

This June, in between visits to the Kalande and Mitumba communities, I was able to spend some time following the twins and their daughters.

They spent much of the morning fishing for termites. Usually there’s more termite fishing in the wet season than this time of year, the early dry season, but perhaps the recent rains had softened up the mounds enough to make it easier for the chimps to stick in their termite fishing tools: wands made of grass or sticks, stripped of leaves to make slender probes.

Golde

Golden eating termites from her fishing wand.

Golden standing quadrupedally and holding her wand in her mouth. (11 June 2014)

Golden standing quadrupedally and holding her wand in her mouth.
(11 June 2014)

Jane Goodall’s discovery that chimpanzees make and use tools to fish for termites was one of the key findings that made Jane and Gombe famous. In The Descent of Man, Darwin argued that the making and using of tools originated after the evolution of bipedalism: walking on two legs freed the hands for manipulation, rather than transportation. It was therefore a surprising discovery that these knuckle-walking forest apes regularly used their hands, not just for walking and climbing, but also for making and using what has turned out to be a large variety of tools.

Tools increase access to important foods that would not otherwisebe available. Termites, for example, are rich in fat and protein, nutrients that are important but not well supplied by the mainstay of chimpanzee diet, ripe fruit.

Golden eating termites from her hand. (11 June 2014)

Golden eating termites from her hand.
(11 June 2014)

Tool use also increases the value of social learning. Termite fishing is a skill that takes years to learn properly, and kids mainly learn how to termite fish from watching their moms. As Elizabeth Lonsdorf elegantly showed with her studies of termite fishing at Gombe (in which Gremlin and the twins figured prominently), girls learn to termite fish faster than boys, probably because boys are too busy playing rough-and-tumble games.

Once cultural learning is established, a whole range of new subsistence strategies can be acquired that any one individual would never think to invent on their own.

Darwin was probably right that being bipedal helps with making and using tools. Chimpanzee hands are long, with curved fingers and short, weak thumbs. Australopith hands are much better suited for both the precision grip and the power grip. They must have had a much broader range of tools than chimpanzees: sticks for digging food and hitting rivals, stones for smashing food and throwing at enemies. But the discovery of tool use and material culture in chimpanzees suggests that these practices may have already been present in our common ancestor with chimpanzees, predating the origin of bipedalism — and perhaps providing increased selective advantages for individuals in those populations that first started standing bipedally a bit more than usual.

Imani standing bipedal to feed. (10 June 2014)

Imani standing bipedal to feed.
(10 June 2014)

Deus and Ramba looking out over Mitumba valley.

Mitumba

On Thursday, 12 June, Deus, Rebecca and I visited the Mitumba community in the North of Gombe.

Gombe is one of the few sites where researchers can study neighboring chimpanzee communities. At most sites, researchers focus on a single study community, and don’t know very much about the neighbors. This was the case at Gombe for many years, but since the Mitumba chimpanzees were habitatuated in the 1990s, we have been able to follow chimpanzees from two communities simultaneously. And now, with monitoring of the Kalande chimpanzees, we can track the movements of nearly every chimpanzee in the park.

The prospect of studying intergroup interactions from both sides of the event is what led me to start working at Gombe, and has been a focus of my research ever since. Deus has played a big part in this, as he collected data on the Mitumba chimpanzees, first as a research assistant on the intergroup relations project, and then as a PhD student.

When I first started working at Gombe, we worried that males from the larger, more powerful Kasekela community would kill the remaining males from Mitumba and take over their range. And sure enough, soon after I started working at Gombe, the young male Rusambo was found dead, with severe wounds, the day after Kasekela males traveled deep into Mitumba’s range (Wilson et al., 2004).

Edgar keeping a close eye on Flirt

Edgar keeping a close eye on Flirt

However, since then, the Mitumba males have held on, and even seem to have expanded their range a bit. And while intergroup incursions from Kasekela have continued, including the killing of the young infant Andromeda (Wilson, 2013),  it is the Mitumba males who have proved a greater threat to themselves. Mitumba males Edgar and Rudi killed their former alpha male, Vincent, in 2004. Soon after, the young male Ebony was found dead. Since then, Edgar and Rudi have fought bitterly and Rudi has disappeared. Edgar seems determined to keep Mitumba for himself, as if he were a gorilla silverback.

When we arrived in Mitumba, we walked up the steep, narrow valley of Mitumba stream. Gnarled old Mgwiza trees grow along the stream banks, and Lusieno trees tower overhead.

 

Flirt climbing down from her feeding tree.

Flirt climbing down from her feeding tree.

We found chimps close to the stream. Edgar followed Flirt closely. She had a full swelling and he clearly wanted to keep her all to himself. Flirt is one of Fifi’s daughters. She was born and raised in Kasekela. She was orphaned when her mother died in 2004, but managed to survive, spending much of her time with older brother Frodo. Flirt is one of the very few chimpanzees I ever saw Frodo groom.

After Flirt reached sexual maturity, she did what female chimpanzees usually do:  transferred to a new community. With Edgar showing so much interest in her, maybe she will conceive an infant soon.

Young male Apple followed them from a distance.  Apple is one of the2014-06-12 Apple sitting in tree A rising generation of Mitumba males, along with Kocha and Ramba. If these boys survive to maturity, then Mitumba may have a chance at keeping Kasekela at bay and maintaining Mitumba as a viable community. But with Edgar’s track record of attacking other males, maybe he won’t let these young competitors survive. If Edgar continues killing all the young males, his line may end in a Pyrrhic victory: eliminating not only his competitors, but his only allies against the mighty Kasekelans.

After coming down from the trees, the Mitumba chimpanzees soon climbed up the steep slide of the hill, giving us a chance to experience some classic Mitumba chimp viewing: crawling on hands and knees through vine tangle.

 

Nyamagoma Valley viewed from Lake Tanganyika.

Kalande

On June 10th, I traveled to the south of Gombe to visit the range of the little-known Kalande community of chimpanzees.

Map of Gombe National Park and chimpanzee ranges (from Rudicell et al., 2010)

Map of Gombe National Park and chimpanzee ranges (from Rudicell et al., 2010)

The Kalande community is one of three chimpanzee communities at Gombe.

The most famous, most intensively studied chimpanzees live in the Kasekela community in the center of the park. These are the chimpanzees that Jane Goodall has studied since 1960. They have the biggest range and the most members of the park’s three communities.

To the north of Kasekela live the Mitumba chimpanzees. This is a smaller community, which Deus Mjungu studied for his PhD research. The Mitumba community has fewer chimpanzees than Kasekela, but is still vigorous. They have a small range, but it includes excellent chimpanzee habitat with lots of food trees.

To the south is the Kalande community (also known as Bwavi). Most of the Kalande community’s range is grassland and woodland, with narrow strips of forest along the stream valleys. We know less about the Kalande chimpanzees than any of the others in Gombe. For the most part, these chimpanzees are still unhabituated, meaning they fear people. Researchers can follow the Kasekela and Mitumba chimpanzees around all day long, but they are lucky to get even fleeting glimpses of Kalande chimpanzees.

We aren’t even completely sure how many chimpanzees live in Kalande. Based on sightings and samples of genetically distinct individuals, there seem to be at least 9 chimpanzees in Kalande, but we don’t know for sure.

Skull from a male chimpanzee found dying in Kalande in 1994 or 1995.

Skull from a male chimpanzee found dying in Kalande in 1994 or 1995.

A small team of researchers monitor the Kalande chimpanzees. They collect fecal samples for genetic analysis, which enables us to keep track of individuals, even when we don’t know what they look like. Kalande has the highest rate of infection with the virus SIVcpz, which likely contributed to the decline of this community (Rudicell et al., 2010). Many females have left Kalande for other communities, both as part of the natural emigration process (females usually leave to join a new community when they are sexually mature), and because as Kalande declined, it eventually came to have too few males. Females seem to prefer living in communities with many males, both because many males are better able to defend the feeding territories that females need to survive and raise their offspring, and because females need unrelated males as mating partners. As the number of adult males in Kalande dropped down to one, or perhaps even zero, some Kalande females left for good, while others seem to have kept their Kalande home base, but visit Kasekela for mating.

Kat and Kazi, photographed when visiting Kasekela (20 April 2006)

Kat and Kazi, photographed when visiting Kasekela (20 April 2006)

Kati, for example, is a Kalande resident who has probably lived there since 1998.  Based on genetic data, we think she is the daughter of Patti who was known as Tita when she was younger. Since 2006, Kati has been making occasional visits to Kasekela. I saw her with her young son Kazi on one of these early visits. Of the Kalande chimps, Kati seems to fear people the least, which would make since if she grew up in Kasekela.

Deus and I took the boat to Kalande, where we met Ashaabu, one of the new Kalande research assistants. Ashaabu got his start working as a village Forest Monitor for his village’s forest reserve (part of the Greater Gombe Ecosystem project). Before going into the forest, we talked with Ashaabu for a while about which chimpanzees he has been seeing.

Kazi, who was just a little boy back in 2006, now seems to be the alpha male of Kalande, even though he is just a gawky adolescent. Based on how old Kazi looked back in 2006, I think he must be at least 12 years old now. Ashaabu says Kazi is around the size of the Kasekela male Fundi, who is about 14. The old male Renadi (or Leonard) hasn’t been seen for a number of years now, and I suppose must be dead. There might be another adolescent male, Pamera, but we don’t know for sure if he is still alive. Ashaabu has regularly seen Kati, Kazai, Katarina (Kati’s new baby), a big female without an infant, an adolescent female (who I think might be Pairott), and another young female around Kazi’s size. (Perhaps this is really Pamera? Might be hard to tell he’s a male if he’s still young and seen only briefly from a distance.) Ashaabu also mentioned Obedina, a female who had a big belly last year who might also have a new baby now.

After talking, we hiked into the forest, climbing a steep rocky path into Nyamagoma valley. Nyamagoma is the southernmost valley of the park, just north of Kazinga village. The path wound through an open woodland with a view of the lake below.

Ashaabu collecting Msongati fruits.

Ashaabu collecting Msongati fruits.

Along the way, we collected fruits and leaves for the isotope and nutrition projects. Given that Kalande has so much woodland, it will be interesting to see if the Kalande chimpanzees, or their foods, differ isotopically at all from those in Kasekela.

Ashaabu and Deus below a chimp nest.

Ashaabu and Deus below a chimp nest.

We followed the path down towards Nyamagoma Stream, where tall trees grew, shading the steep valley in green light. We didn’t see any chimpanzees, but we did see a number of nests. Chimpanzees build a new nest (or bed) in trees each night to sleep safely out of reach of any predators that might be lurking about. We found one cluster with five fresh nests, suggesting that up to seven chimpanzees might have slept there (if the group included Kati and Obedina and their new babies). It was encouraging to see so many fresh signs of chimpanzees using this valley. The Kalande community is still hanging in there, and perhaps they might recover, if the Kasekela males don’t catch Kazi and finish him off.

Ashaabu taking data on his tablet.

Ashaabu taking data on his tablet.

Ashaabu carried with him the tablet computer he had used as a Forest Monitor. He used the tablet to take pictures of the nests and enter the data, including GPS locations of the nests. It was quite stunning for me to think each of the villages around Gombe now has its own Forest Monitors, collecting data like this on their own village forest reserves, and loading it up regularly into the Cloud.

 

 

 

 

 

 

 

 

Director of Chimpanzee Research for Gombe Stream Research Centre.

 

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Freud eating termites 
(02 Nov 2006)

Isotopes and Isoptera

My main goal in visiting Gombe this trip was helping my graduate student, Rebecca Slepkov Nockerts, get started with her project on the stable isotope ecology of chimpanzees and baboons at Gombe.

Over the past couple of decades, stable isotope studies have revolutionized the study of the diets of human ancestors.

Isotopes are variants of chemical elements that differ only in the number of neutrons. For example, carbon has three naturally occurring isotopes, of which Carbon-12 (12C) is the most common. All carbon atoms have 6 protons – that’s what makes them carbon atoms, and not some other element. 12C has 6 protons and 6 neutrons, and is stable – each atom can last for billions of years. Carbon-14 (14C) is a radioactive isotope of carbon. It has 6 protons and 8 neutrons – which makes it unstable. It gradually decays, turning into Nitrogen-14 while spitting off an electron and an electron anti-neutrino. By geological standards, 14C  decays relatively quickly, making it useful for dating objects containing carbon that are up to about 60,000 years old.

The third naturally occurring isotope of carbon, 13C, has 6 protons and 7 neutrons, and is stable, though  much less common than 12C. For the most part, chemical reactions  involve interactions among electrons, and to some extent protons. Neutrons don’t get involved. As a result. 13C behaves chemically almost exactly like 12C. However, in some reactions, the slightly different mass of the heavier isotopes can make a difference. For example, in photosynthesis, molecules containing 13C move more slowly, because they are heavier, and end up in different proportions in the final product.

As it turns out, several different major groups of plants use different mechanisms of photosynthesis, which produce distinct isotopic signatures. Especially important in paleoanthropology are C3 plants (most plants, including most forest species) and C4 plants (certain plants adapted to hot dry climates, including many tropical grasses and sedges).

Unfortunately, all of these different numbered C’s quickly get very confusing! But the main thing to remember is that C3 = forest, C4=grass.  Chimpanzees mainly eat C3 forest plants. Even in dry woodlands, chimpanzees eat mainly forest plants: fruit, seeds, flowers and leaves from trees, vines and shrubs growing along rivers and streams. In contrast, baboons eat more C4 plants – especially grass seeds and corms. Similarly, stable isotope studies of fossils have found that early hominins ate mainly Cplants (and/or animals that ate Cplants), whereas later hominins at more C4 plants (and/or animals that ate C4 plants).

However, all of these inferences about hominin diet depend on some assumptions about how different tissues reflect diet. Unfortunately, studies comparing hominin isotope signatures to those of living species usually use different tissues. Studies of fossils usually use tooth enamel, which is extremely stable and thus is thought to maintain a good record of the living animal’s isotope signature for millions of years after death. Studies of living primates, however, usually use tissues that are easier to obtain, such as hair and feces, because it is hard to get tooth enamel from living animals (which are generally busy using their teeth). We therefore don’t know nearly enough about how diet translates to isotope signatures across these different tissues in living species. This is what Rebecca plans to find out.

Freud eating termites  (02 Nov 2006)

Freud eating termites
(02 Nov 2006)

The long-term study of chimpanzees and baboons at Gombe brings together the key pieces needed for this study: expertise in identifying and collecting the important food species, long-term records on diet, and skeletons from known individuals. For example, we have a lifetime of data on chimpanzees like Freud, pictured here in November, 2006 eating termites.

Rebecca and Deus examining the bones of Freud the chimpanzee

Rebecca and Deus examining the bones of Freud the chimpanzee

Freud recently died, at nearly 43 years of age (making him one of the longest lived Gombe males). Thanks to concerted efforts over the years by people at Gombe Stream Research Centre, the skeletons of Freud and many other well known individual chimpanzees and baboons have been preserved. Thanks to a lifetime of data on these individuals, we know a lot about what they have been eating. This comprehensive data on individuals will provide an unparalleled amount of detail for matching up diet to isotope signatures of different tissues.

It is particularly interesting to look at chimpanzees and baboons at Gombe because these two quite similar species differ somewhat in their diets in ways that parallel some differences between early and later hominins: baboons eat more grass than chimpanzees, just as later hominins appear to have eaten more grass (and/or grass-eating animals) than earlier hominins.

Rebecca and baboons collecting grass samples

Rebecca and baboons collecting grass samples

We are working together with Carson Murray and Rob O’Malley, who are conducting a nutritional study of chimpanzees. Both the nutritional study and the isotope study need foods to be collected, so we will work together to collect foods and share samples.

Rob did his PhD work at Gombe, studying insectivory by chimpanzees. Chimpanzees and baboons both eat a wide range of insects at Gombe.

Termites emerging from the nest

Termites emerging from the nest

On our first day in the field, we were lucky to catch an emergence of flying termites (“kumbi kumubi” in Swahili). These members of the infraorder Isoptera are one of the most important insect foods, not only for chimpanzees and baboons, but also many birds, monitor lizards, and even people.

Rebecca and Rob collecting termites.

Rebecca and Rob collecting termites.

We also found a nice column of Dorylus army ants (“siafu” in Swahili).

siafu jaws

Column of army ants showing off their jaws

Army ant soldier biting Rob's thumb.

Army ant soldier biting Rob’s thumb.

From an isotopic perspective, insects like termites and army ants may be interesting mainly for another isotope, Nitrogen, which provides information about where an animal gets its protein from. The higher the animal’s trophic level (the higher it is in the food chain), the more enriched its tissues are in the heavier Nitrogen isotope, 15N. It will be interesting to see whether chimpanzees and baboons at Gombe differ in their Nitrogen isotope signatures, and whether the isotopic signatures of individual chimpanzees relate to how much meat or insect matter they ate while alive.

At the night meeting, Rob and Rebecca explained their projects to the chimpanzee field staff. Rob talked about nutritional differences that he had found between ants and termites. I noted that “even people like to eat termites, right?” The field assistants responded with many people talking at once. The general consensus: “We like to eat termites, yes, but we like locusts even better!”

And I have to agree. Termite sauce with mushrooms is okay but seems a bit buggy to me, whereas fried locusts quite tasty.

thoughts on primates, people, and evolution