There are a lot of theories about why humans don’t have any fur. We’ve narrowed it down to the 3 leading theories for you.
Of the 5,000+ mammal species on Earth, very few are naked. We are one of them. The basic reason we have no fur is that it must have been an evlutionary advantage:
“All [no fur theories] revolve around the idea that it may have been advantageous for our evolving lineage to have become less and less hairy during the six million years since we shared a common ancestor with our closest living relative, the chimpanzee.” – Mark Page/Scientific American
“Why are we the only hairless primate?”
THEORIES BEHIND WHY HUMANS LOST THEIR FUR:
1. HEAT THEORY = Africa was hot when we were evolving. Real hot. Walking upright got us up and away from the hot soil. Losing our fur allowed us to lose heat more easily. Sweating increased evaporative cooling and cooled us down. Once we got upright and started to walk around in the sunny savannah we were no longer in the cool forest of our ape ancestors and we had to lose the fur to make it easier to rid ourselves heat.
2. AQUATIC APE THEORY = 6-8 million years ago our apelike ancestors lived a semiaquatic lifestyle. They foraged on foods found in shallow waters. Hair is a terrible insulator in water, so we lost it like the dolphins and whales did. (this one kinda sucks to us, it doesn’t have much palentological support, and just looks a seals and walruses.)
3. PARASITE THEORY = It’s no secret that fur hides ticks, lice, flies, and other nasty ectoparasites. These creatures aren’t just annoying and blood sucking, but they bring deadly illnesses like one of the world’s number one killers: malaria. As human’s brains grew (largely due to the ability to successfully hunt, cook, and eat meat) we became smart enough to make clothes, build shelters, and create fire. This enabled us to lose the fur to avoid the parasites while being able to stay warm at night with our shelter/fire/clothing combination.
We know, all of this begs the question: “Why did we keep the head and pubic hair?”
“Despite exposing us to head lice, humans probably retained head hair for protection from the sun and to provide warmth when the air is cold. Pubic hair may have been retained for its role in enhancing pheromones or the airborne odors of sexual attraction.” – Mark Page/Scientific American
Ok, then the final question: “Why do girls have less hair than boys?”
“Once hairlessness had evolved this way, it may have become subject to sexual selection—being a feature in one sex that appealed to another. Smooth, clear skin may have become a signal of health, like a peacock’s tail, and could explain why women are naturally less hairy than men and why they put more effort into removing body hair.” – Mark Page/Scientific American
The one thing we’d like to point our is that our hair loss could very well have been a combination of the first and third theories above. Scientists don’t win grants on combining other peoples theories, so it’ll be a while before this is explored.