It's obvious that humans are unlike all animals. It's also obvious that we're a species of big mammal down to the minutest details of our anatomy and our molecules. That contradiction is the most fascinating feature of the human species.

The chapters in The Third Chimpanzee on the oddities of human reproductive biology were later expanded in Why Is Sex Fun? Here, they're linked to Diamond's views of human psychology and history.

Diamond is officially a physiologist at UCLA medical school, but he's also one of the best birdwatchers in the world. The current scientific consensus that "primitive" humans created ecological catastrophes in the Pacific islands, Australia, and the New World owes a great deal to his fieldwork and insight. In Diamond's view, the current global ecological crisis isn't due to modern technology per se, but to basic weaknesses in human nature. But, he says, "I'm cautiously optimistic. If we will learn from our past that I have traced, our own future may yet prove brighter than that of the other two chimpanzees." --Mary Ellen Curtin