You only need to read the first two paragraphs of The Naked Ape to understand why it was so controversial when it debuted in 1967 and why it wound up on lists of banned books deemed “anti-Christian” by school boards. Morris, a zoologist, defines humans as hairless apes; he explores the conflict between our animal impulses and our loftier aspirations as matters of biology, not morality. We are the most sexual of primates, he says, and that sexuality has shaped modern civilization — not the other way around. Sure, no other animal creates art, nor do they obsessively analyze themselves. But thanks to our unique upright posture, we’re also the only primate whose secondary sex characteristics are on display whenever we interact, as Morris explains in detail. And we’re also unusual in that we mate to bond with each other as well as to procreate. All that makes for some serious biological tension, and Morris’ landmark views on why we evolved this way are fascinating — even in an age when the idea that we’re not all that different from our animal cousins isn’t quite so revolutionary.