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To have one chimp act as a model for another, however, is easier said than done. I can instruct a coworker to demonstrate a particular action ten times in a row, but try telling that to an ape! So first we constructed a puzzle box that can be opened, for example, by using a stick to lift a lever, causing a treat to roll out. We then teach the technique to one member of the group, usually a high-ranking female, and let her demonstrate it for others. Allowed to watch and imitate their groupmate’s new skill, chimps entirely live up to their reputation as apes. They’re literally in one another’s faces, leaning on one another, sometimes holding the model’s hand while she’s performing, or smelling her mouth when she’s chewing the goodies she has won. Such close personal contact—which would be far too dangerous for a human experimenter—makes all the difference. Our chimps often replicate the observed actions even before they’ve gained any rewards themselves. That brings me back to the role of the body.

How does one chimp imitate another? Is it because he identifies with the model chimp, and absorbs her body movements? Or could it be that he focuses on the puzzle box? Maybe all he needs to know is how the thing works. He may notice that a door slides to the side, or that something needs to be lifted up. The first kind of imitation involves reenactment of observed manipulations; the second merely requires technical know-how.

Thanks to ingenious studies by Whiten and others, in which chimps were presented with a so-called ghost box, we know which of those two explanations is correct. A ghost box derives its name from the fact that it magically opens and closes by itself. If technical know-how were all that mattered, such a box should suffice as a teaching tool. But in fact, letting chimps watch a ghost box until they’re bored to death—with its various parts moving and producing rewards hundreds of times—did not teach them anything.

In order to learn from observation, apes need to see actual fellow apes perform an action. Imitation requires identification with a body of flesh and blood. We’re beginning to realize how much cognition in humans and other animals runs via the body. Indeed, bodies figure in everything we perceive or think. The same hill is assessed as steeper, just from looking at it, by a tired person than by a well-rested one. An outdoor target is judged farther away by a person burdened with a heavy backpack than by one without it.

The field of “embodied” cognition is still very much in its infancy, but it has profound implications for how we look at human relations. We involuntarily enter the bodies of those around us so that their movements and emotions echo within us as if they’re our own. This is what allows us, or other primates, to re-create what we have seen others do. Body mapping is mostly hidden and unconscious, but sometimes it “slips out,” as when parents make chewing mouth movements while spoon-feeding their baby.

The same can be seen in other animals. Katharine (Katy) Payne, a biologist at Cornell University, once saw an elephant mother do a subtle trunk-and-foot dance as the elephant’s son chased a fleeing wildebeest. “I have danced like that myself,” writes Payne, “while watching my children’s performances—and one of my children, I can’t resist telling you, is a circus acrobat.”

Not only do we mimic those with whom we identify, but mimicry in turn strengthens the bond. Human mothers and children play games of clapping their own and each other’s hands in the same rhythm. These are games of synchronization. And what do lovers do when they first meet? They stroll long distances side by side, eat together, laugh together, dance together. In romantic situations, a woman will feel better about a date who leans back when she does, crosses his legs when she crosses hers, picks up his glass when she lifts hers, and so on.

This familiar effect may explain why music is just as universal in human societies as language. When many people listen together to the same music, mood convergence and bonding are the result. Examples of similar bonding in other animals are easy to come by, from howling howler monkeys to roaring lions. Take large black gibbons called siamangs, which sing high up in the trees in the Malay and Sumatran forests where they live. For many animals, it’s the male’s job to keep intruders out, but with siamangs—which live in small family groups—both sexes work together toward this end. The female produces high-pitched barks, whereas the male often utters piercing screams that at short range will put every hair on your body on end. Their wild and raucous songs grow in perfect unison into what has been called “probably the most complicated opus sung by a land vertebrate other than man.”

It takes time for a pair of siamangs to learn to sing in harmony, and harmony may be critical to holding onto a partner or territory. Other siamangs can hear how close a pair is, and will move in if they discern discord. Thomas Geissmann, a primatologist at the University of Zürich in Switzerland, observed that deserting an established partner would not be a very attractive option, because the duets of new couples are noticeably poor. He found that couples that sang together a lot also spent more time together and synchronized their activities better. One can tell a good siamang marriage by its song.

According to Ulf Dimberg, a psychologist at Sweden’s Uppsala University, we don’t decide to be empathic—we simply are. Having pasted small electrodes onto his subjects’ faces so as to register the tiniest muscle movements, he presented them with pictures of angry and happy faces on a computer screen. Humans frowned in reaction to angry faces and pulled up the corners of their mouths in reaction to happy ones, even if the pictures flashed on the screen too briefly for conscious perception. That is a rather primitive kind of empathy known as emotional contagion—a first step on the road toward full-blown empathy.