No more body hair
3.3 million years ago
Humans are the nearly-hairless apes. No one knows why, but it happened 3-4 million years ago. That’s when pubic lice evolved, which could only infest us once our other body hair was gone. Exposed to the Sun, our skin darkened. From then on all our ancestors were black, until some humans left the tropics.
See other: What Makes Humans Human?