Why did our ancestors eventually lose their body hair?
This is actually quite a big question in hominin evolution. Since body hair is not one of those things that fossilises well, we aren’t even sure *when* human ancestors started losing their fur, so we can’t know what the environmental pressures were at the time. Hypotheses that have been put forward include: heat regulation in a very warm climate; less water resistance and a better ability to swim as human populations migrated to riverbanks, lakesides and seashores (environments that actually were very important for nutrition during one stage of human evolution, as there is evidence that at some stages Homo species depended quite a lot on shellfish); or to aid group cohesion by enabling better social signalling. This last is rather interesting, and provides some explanation for why we have retained the patchy bits of hair that we have. With less hair on our faces, our expressions become easier to read — and the bits of fur that remain, like eyebrows, actually *enhance* expressions — a
One hypothesis is that in days before pesticides and detergents, hair attracted dirt and harboured parasites (fleas, lice, blowfly larvae etc). Less hair meant it was easier to pick off the parasites, and made it harder for parasites to secrete themselves on the human body. Being parasite free is very important for communal living, as everyone knows if their kids suddenly come home with nits. So people with less hair may have advanced better in densely populated, organised societies. It is notable that humans who settled in the world’s tropical regions, regions where parasites are most prolific, are also often the least hairy. We didn’t however, evolve to lose the hair on our heads because it provides good heat insulation to our brains, acts as an excellent sunscreen and can provide a cushioning affect against a blow to the head. People who had less head hair have higher rates of skin cancer on the scalp, so it isn’t an evolutionary advantage to lose hair from the scalp.
