Very few animals indeed have such a strange hair growth pattern as that of humans. If you imagine any other animal with only hair on their head, you realise that it is unusual (not to mention funny), and is just as unique as a peacock’s tail.
Our entire body is covered in a thin layer of hair, except our head. Sure, some people have more body hair than others, but head hair is by far the thickest on the body, even for those who are hairier than normal (ok, the exception is bald, hairy men, but there are other reasons for this). So why do humans have a lot of hair on their heads, but not much on our body?
The head has a large surface area and a large blood supply, which means large amounts of heat are lost through the head. Having hair on your head acts as an insulating layer, which prevents heat loss. The body loses less heat per unit area compared to the head, which is probably why we have lost some of our body hair, but kept head hair. In addition to this, wearing animal skins and clothes on our body would have reduced the need for body hair.
Heat retention is probably the most likely, and important factor for the reason we have head hair, but there are other potential reasons which may have also contributed to some degree.
This is a favorite theory of our evolution, and although it is lacking some real evidence. Sometimes referred to as ‘water-ape’, this theory suggests that as early man we grew up by the coast. Here we could hunt for food on land, but also wade out to sea to search for food. Imagine an ape wading out to sea and coming back – they would be dripping wet, and would get cold. So, we evolved to lose our body hair, so we wouldn’t stay wet for so long once out of the water. The hair on our head remained to retain body heat, but also because our heads didn’t really go underwater, because we needed to breath.
Although not an accepted theory of evolution by most people, losing body hair but head hair would offer an advantage to early humans looking for food at sea.
Besides, how else do you explain why humans and sea mammals have a similar bone structure in the flipper and hand? Why would a whale or dolphin need those bones in its hand? Food for thought, but not concluding evidence.
Hair decoration to attract a mate has been going on for an incredibly long period of time, and our ancestors have gone to great lengths to gather special gels to make their hair ”attractive”. Ancient bog body discoveries almost always find that the person had gone to a surprising amount of effort to have their hair in a certain way. It is possible that having a good head of hair 3000 years ago would have increased your chances of getting a mate, and passing your hair genes on.
Ok, so 3000 years is not long in terms of evolution, but this does offer a bit of support as to why head hair has endured the test of time so well. This also mirrors this explanation for the purpose of the aforementioned peacock’s tail. potentially more truth here than you think…
The most acceptable, and most probable reason for having hair on our heads and not the rest of the body is to retain heat. We probably lost the matching body hair because we started wearing animal skins/ clothes which made body hair redundant.
It is of course possible that there are other contributing factors which have ensured an advantage to those who are particularly folically gifted; and they may include the ‘water-ape’ theory and using hair as a tool to attract the opposite sex.
Picture courtesy of MorkiRo
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It is an evolutionary adaptation for the need to keep our heads warm to conserve heat. Clothing meant that we didn’t need body hair so much, so that gradually was lost.