A few years back, during a family visit to northern Minnesota, we came across the Hibbing Ethnic Festival. My brother-in-law, who lived in California, thought this was hilarious, as Hibbing is about 97% white.

“What ethic diversity?” he asked. “Swedes AND Norwegians?”

And sure enough, the Swedish, Norwegian, Finnish, Estonian, Latvian, Lithuanian, Russian, Welsh, Cornish, and other people that immigrated into Hibbing and other Iron Range towns were pretty much all pale-skinned Europeans. But they were not yet White. They were members of mutually hostile tribes. They spoke different languages, had different customs, different churches, and maintained deep suspicions towards one another.

Mom’s maternal grandparents were Swedish and Norwegian. At the time, this was a mixed marriage. Now we have a hard time remembering who was the Swede and who was the Norwegian. But at the time it was a big deal. And their daughter, my Grandma, once told me that in high school there was a boy who was allowed to come visit with her on the porch, but he was not allowed inside the house, because he was a Finn.

Nowadays, I think the Swedes and Norwegians and even the Finns get along just fine up on the Iron Range – and many of them are so intermarried through so many generations that ethnicity is just something to remember at the Ethnic Festival, if they still have it, when they need to decide who bakes the pasties, and who brings the lutefisk.

And we have such a universally favorable opinion now of the Norwegians – with their fjords and nice sweaters – that the news of the recent shooting just seemed unbelievable. We’ve grown used to Americans doing that sort of thing, but Norwegians?

The shooter, Anders Breivik, apparently thought that he was providing a wake-up call to save Norwegians and other Europeans from cultural and demographic suicide. According to his manifesto, he believes that Norway is being overrun with foreigners, many of them Muslim.

As part of an effort to understand why people can have such hostility to outsiders, Rhitu Chatterjee from PRI’s The World interviewed me, Frans de Waal, and Samuel Bowles about the evolutionary roots of xenophobia (fear of strangers). In this story, I get quoted mainly talking about the nasty side of chimpanzees, while the others get quoted talking about how nice bonobos and humans can be. Which I suppose is fine, since much of my work focuses on how and why chimpanzees can be so nasty to each other. But now that I have a blog, I can add a few of my own words about how and why people are different from chimpanzees.

Male chimpanzees spend their whole lives in the same community. They never leave their territory, which may cover 5 to 25 or more square kilometers (something like 2 to 10 square miles). They are perfectly capable of walking further than that, but in a world of chimpanzees, you can only go so far before running into another community’s territory.

Chimpanzees live in a zero-sum world. The only way they can get more stuff is by taking it from others. Their food supply depends on their territory. If they want more food, they have to take more territory from their neighbors. And if a male were to immigrate into another community, he would have nothing to offer the resident males. He would just be another competitor in the mating game – and even worse, he would be an unrelated competitor. If you’re a chimpanzee competing for mates against your father or brother or half-brother or cousin, it’s not so bad if you lose, because you share some of your genes with your kin, and those will get passed on. But losing to a stranger? That’s a total loss.

Humans, in contrast, have created a world that’s not zero-sum. When we meet strangers, we don’t have to knock them over the head and take their stuff to benefit from them. Instead, we can trade with them, to our mutual benefit. Even better, if we trade with someone this year instead of knocking him over the head, he might come back next year with more stuff that we want. We can also benefit from immigrants. When my great-great grandfather Anton came over from Sweden, the resident males in northern Minnesota didn’t gang up on him and kill him. Instead, they hired him to work in the iron mine. There were already lots of people living in the United States when Anton immigrated, but there weren’t enough of them willing to live up north and do the difficult, dangerous work of iron mining. So the mine owners, and the steel workers, and the people who used steel for their farm tools and anything else, all benefited from these immigrants. And it was dangerous – Anton died in the mine a month before his thirty-third birthday, when a block of stone fell on his head, leaving behind a young widow with a baby boy.

In the late 1800s, Norway and Sweden were poor countries with rapidly growing populations, and many people left for the US, where they and their descendents lost their tribal identities and became Americans. Now Norway and Sweden are rich, with slowly growing and rapidly aging populations. These countries need immigrants, and the immigrants are coming in from Eastern Europe, the Middle East and North Africa.

The United States has its share of ethnic conflict and resentment towards immigrants.  But it’s even trickier for the European countries. Being American depends on citizenship, not ethnicity. But in Europe, following the fall of empires and the rise of democracy, national boundaries were drawn around ethno-linguistic groups. It’s going to be a challenge for countries based mainly on old tribal boundaries to absorb these new immigrants. But with an aging, low fertility population, an increasing number of new immigrants will be needed to keep the European economies going. And as long as the countries to the south and east of Europe have growing populations and few job prospects at home, there will be lots of people knocking at the door.

But the amazing thing, from the perspective of a chimpanzee, is that people do this at all.