So, why did humans lose their hair, anyway?

Ever wondered why we’re the only primate species that doesn’t have body hair? Of course, no one knows for sure, but there are some theories.

Did we go through a semi-aquatic phase in our evolution and so shed our hair for efficiency in the water much like whales? Perhaps, when we left the trees for the African Savanna, we got too hot in direct sunlight. Never heard of the former. Not sure if I buy that one. The latter seems reasonable.

But, have you heard of this one? We did it for hygiene reasons.

This New York Times article suggests that we lost our hair because body hair attracts parasites — Lice, fleas and ticks — and the diseases that go along with them.

They did comparisons of when we began to go hairless and when we started wearing clothing. These periods coincide nicely with the introduction of Body lice. The theory goes that when our skin was covered in hair, we were infested with lice, much like the head lice of today. When we evolved into the hairless state in which we exist today, those lice became confined to the head where hair remained. When we started wearing clothing to compensate for the loss of hair and to give ourselves the ability to migrate to more temperate climates, the head lice evolved into a body lice that occupies the clothing (body lice can’t survive on the skin. They exist in the clothing). So, the discovery of clothing and body lice give an estimate as to when we lost our hair, which is about 50,000 years ago.

As a side note, the article talks about the fact that as the hominid ventured away from the shade of the trees on the savanna and shed their body hair, they evolved the darker skin pigmentation seen on the peoples of Africa today. It explains that evolution selected for this darker pigmentation because of its advantages in reflecting away the sun’s UV radiation which is harmful to the body.

What it doesn’t explain is something that has been a curiosity of mine for some time. As we all know, anyone who wears a black shirt on a hot, sunny day will be much hotter than an individual wearing white clothing because of the latter shirt’s ability to reflect the heat away from the body. So, here’s my question. How do we reconcile the fact that nature selected for UV protection over the ability to dissipate heat? Was the latter simply an easier problem to overcome by other means (vasodilation, sweating)?

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2 comments on “So, why did humans lose their hair, anyway?

  1. I don’t have a definitive answer to your question, Kyle, but if you look around you at all the people who are going bald at younger and younger ages, I could argue reasonably that we’re just not done evolving. In time, perhaps we’ll all be hairless, including the pubes and head.

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