Why did the first humans lose their ape-like hair as they evolved?....?

Question

..AND why did their hair not grow back again when they migrated out of Africa to colder climates?

Answer 1

No one really knows for sure. Much like the ability to use language, body hair just doesn't appear in fossils, so it's impossible to say for sure when it happened.

Perhaps it happened as the Australopithecines were moving onto the savannah from the trees, and is related to the increased running and hunting activity and greater need to shed excess body heat by sweating. Perhaps it is related to semi-aquatic adaptations as proposed by the Aquatic Ape proponents (a neat little hypothesis that unfortunately has no fossil evidence to back it up). There are some who think that it might have to do with species recognition and signalling - a marker that visually identifies the species to others of the same species. This could be why we have retained hair in the areas that also have the most active scent-producing glands (groin and underarms) - for scent recognition. And why males have beards and females don't (instant sexual identification).

It should also be noted that we haven't actually lost the hair. Most humans have pretty much exactly the same number of hair follicles on their body as a chimpanzee, it's just that ours tend to be much finer, thinner and shorter in length than the chimps.

So there's quite a lot of speculation about this question, but not a lot of hard answers. It's fairly easy to come up with hypotheses and wild-*** guesses, virtually impossible to prove any of them.

Answer 2

Like Ron said - the cooling mechanism. The human lifestyle involved running and walking long distances (hunting and gathering) and being better able to keep cool was an adaptation. As far as not growing back. if the gene that involves growing hair was pretty much lost through evolution is cannot come back - just over time it would have to be advantageous for hairier people to be better survivors and pass along their genes - not necessarily the same as the "ape-hair" to grow hair - but with clothing that wasn't necessary.

Answer 3

I pretty much agree with Jaysoos. It is important to realize that we don't know when our ancestors "lost" their hairyness. There are assumptions that Homo erectus (a possible ancestor) was hairless because it was believed to be a persistence hunter, i.e. it ran down prey over great distances but there is really no fossil evidence. Our depiction of Neanderthals as being similar in hairyness to us is also speculation. There are benefits to hair such as protection from cuts and sun. Some persistence hunters such has wild dogs kept their hairyness because the benefits the hair outweighed the benefits of losing it. It seems reasonable that lack of hair helped increase our ability to cool ourselves in a long chase. Our upright posture helps increase maximum wind exposure across our bodies while minimizing the mid-day sun exporsure. The hair on top of our head also helped protect from the direct radiation of the mid-day sun. I think humans may have the best radiator of any mammal, which is extremely advantageous to a predator

Answer 4

There is a theory called the Aquatic Ape Hypothesis. This is a theory that humans, at some time in their evolution, had partially adapted to a marine environment. This theory had first been proposed by an English marine biologist named Alister Hardy and was held to explain a host of differences between Homo sapiens and the rest of the great apes, among them: relative hairlessness, subcutaneous body fat, bipedality (to make swimming and wading more efficient), a "diving reflex" to prevent drowning in infants, our horrendously inefficient water management system, our lack of fear of the water, the webbing some people have between their fingers and toes, and so on.

The whole idea of evolution does make sense to me although some certain specific theories some time lack credibility. To me the Aquatic Ape Hypothesis lacks credibility.

Answer 5

We probably lost the hair because of the development of sweat glands for cooling, also the skin needs to be exposed to sunlight to produce vitamin D. As far as not getting it back in the northern climates our migration has been "relatively" recent and also the developement of clothing.
Ron

Answer 6

they lose their hair due to a mutation in their genes
rare cases, two families in the world have this gene called hypertrichosis

as they evolve, the genes just shut down and it passes on to the offsprings
but, in rare cases, some parents has the gene activated and has this condition

Answer 7

Apes have FUR, not hair.

And when we left Africa, we had fire (for sure) and clothes (probably) to stave off the cold.

Answer 8

Because they already were wearing animal skins at night when it got cold, even in warmer climates. it was not necessary to regrow hair when humans already wore animal skins.

Answer 9

There is no evidence humans ever had ape-like hair.

Answer 10

Because they evolved into clothes.