You don't have to be a biologist or an anthropologist to see how closely the great apes—gorillas, chimpanzees, bonobos and orangutans—resemble us. Even a child can see that their bodies are pretty much the same as ours, apart from some exaggerated proportions and extra body hair. Apes have dexterous hands much like ours but unlike those of any other creature. And, most striking of all, their faces are uncannily expressive, showing a range of emotions that are eerily familiar. That's why we delight in seeing chimps wearing tuxedos, playing the drums or riding bicycles. It's why a potbellied gorilla scratching...