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2007

Monkey See, Monkey Do
Forbes.com, August 28, 2007
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William McGrew spent much of the 1970s observing chimpanzees in Tanzania. One day the chimps did something odd. As two chimpanzees groomed each other's hair, they each lifted an arm overhead. They clasped hands, forming a kind of primate A-frame.

McGrew and his collaborator, Caroline Tutin, had just spent months observing another chimpanzee community just a hundred miles away, and they had never seen that gesture before. But at their new field site, the A-frame handshake turned out to be common.

A special chimpanzee handshake may not seem like much of a discovery, but McGrew realized that it could change the way we think about human nature itself. In our own species, handshakes are a sign of culture. Travel the world, and you'll find a dizzying range of handshakes and other forms of greeting, from the military salute to the cheek kiss, to the high five, to the hongi of New Zealand--pressing noses to exchange a sacred breath. These greetings are not hard-wired into our genomes. Each one was invented in a particular place and time, and then spread from one person to another. It's the same process that has given rise to all the cultural variation that makes humans so endlessly interesting, from languages to dances to technology.

Biologists long believed that culture is unique to humans, because it depended on qualities that only humans were believed to possess--things like the capacity for language and imitation. Animals simply acted on individual instinct; they couldn't follow trends. And yet McGrew saw what looked like a local chimpanzee custom.

Over the past three decades, scientists have steadily amassed more examples of culture in animals. Most of the evidence comes from chimpanzees, which have more than 40 documented examples of cultural variation. Some chimpanzees fish for ants with short sticks, for example, eating the prey off the stick one by one. But others catch many ants on a long stick, which they then sweep into their mouths with their free hand. In one community of chimpanzees in Tanzania, males rip leaves with their teeth as part of their courtship ritual. In Senegal, male chimps use the same gesture as a display of aggression toward other males.

But chimpanzees are hardly the only animals with signs of culture. Even bumblebees seem to follow trends: If experienced bees pick flowers of a particular color, inexperienced bees will follow suit.

Some critics have asked whether these trends have anything to do with human culture. Maybe chimpanzees have developed termite-fishing styles without imitating each other, for example. Maybe each chimp tries to solve the problem of eating termites on its own, or their different styles arise because the termites themselves are different from place to place. Other critics have wondered whether any animal, including our closest ape relatives, have sufficient mental firepower to drive a trend--the ability to teach and to imitate, for example.

Recently, scientists at Emory University in Georgia and St. Andrews University in Scotland collaborated on a series of experiments that document the birth of chimpanzee traditions. In one of the experiments, they presented captive chimpanzees with a box with a piece of food stuck inside. To get it out, they could either stab it with a fork to lift it out, or use another tool to slide it out sideways.

The scientists took a single chimpanzee from its group and taught it one of the techniques. When the chimpanzee returned to its group, the other apes could watch it get the food out of the box. Over time, the other chimpanzees in the group started getting the food out of the box as well, and they almost always used the same technique as the first chimpanzee. And when another untutored group of chimpanzees could watch them, they picked up the same technique as well.

Andrew Whiten, one of the leaders of the project, recently joined with orangutan expert Carel van Schaik of the University of Zurich to ponder what these sorts of results mean for the evolutionary roots of human culture. They argue that those roots reach back hundreds of millions of years, to our invertebrate ancestors, which could gather simple bits of information from other members of their species. As vertebrates with more complex brains evolved, this social learning became more complicated and sustained, turning into long-running traditions--things like birdsong dialects or the site on a coral reef where fish gather to mate.

Complex animal cultures seem to be limited to apes and monkeys (along with whales and dolphins, some evidence suggests). What these animals all have in common are big brains. According to one hypothesis, those big brains evolved as a result of the big groups primates lived in. The big-brained primates that did a better job of keeping track of all the other primates in their band could climb its hierarchy and have more offspring. Those expanding brains, Whiten and van Schaik argue, could also do other things: They allowed primates to learn from other primates and store even more memories of what they learned.

Of course, a lot of the trends our ancestors started to pick up didn't help them much one way or the other. The primatologist Jane Goodall once noticed a female chimpanzee waggling her wrist for a few days. Her best friend start waggling her wrist as well, but after a few weeks, they both gave it up.

Yet a capacity for trends could also mean the difference between life and death. Learning a new way to crack open fruit during a drought could mean the difference between life and death. In fact, Whiten and van Schaik argue, culture was not merely a side effect of an expanding brain. The benefits of culture may have favored even more brain evolution, particularly in our own lineage--the one with the biggest, most powerful brain of all. So next time someone tries to teach you a secret handshake, be grateful that you can learn it.


Copyright 2007 Carl Zimmer
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