Is it because it takes millions of years? Or is there an adaptive advantage even in cold climates? Or no reason at all?
Humans didn’t lose all their body hair. It became finer. I’m not sure there’s a question of why they didn’t regain coarser and better insulating hair because I don’t know if humans ancestors ever had hair that would be beneficial to life in colder climates to regain.
No need, clothing is better. We evolved to develop tools and manipulate our environment.
Agree, but one could argue the one area of our bodies that still maintains a thick patch of hair is the one that’s covered by clothing in nearly every human society. Why is that? But, generally, I agree that the invention of clothing blunted the need for body hair and enabled humans to inhabit every place they could reach.
I’ve read arguments that pubic hair has other purposes, namely for capturing scents that are important in mating. Hair on the head/face may also have mating/attraction uses. The problem is that many of these theories seem to be rationalizing after the fact, not really offering proof.
I’m sorry for this slight hijack…
I think I understand the basics of evolution as a whole but it’s the small increments that I struggle with. Regarding body hair for example, growing it is ‘expensive’. So one human is born with slightly less course hair in a new environment, how is that minor difference enough to cause the course hair trait to die out? It doesn’t seem like environmental pressure would keep course hair man from reproducing.
I hope that’s clear
Actually, the one place that still has thick hair is the scalp. This is the one area of the body that is harder to clothe and loses heat more easily than the rest of the body.
Presumably, by the time himans spread to colder climates they were making clothes, so were sufficiently insulated that thicker hair was unnecessary. Although, speaking for myself, I’m halfway to growing a pelt… Interesting that hairiness is also more common in males, who presumably were outdoors hunting more often in inclement weather; and beards too. Although sexual differentiation seems to be a factor. (And baldness is a later-in-life adpation for men, poutdoors more in cold sunny climates, to get more vitamin D. )
Pubic hair allegedly has value in protecting a sensitive area, and there are other speculations - it retains pheromones easier (hence, becomes available when puberty sets in). Other suggestions were it is an indicator of maturity, a signal “ready for breeding”.
Remember too that our general bodily hair deficiency is alleged to be so that we can shed heat easier, as humans’ ability to run long distance was our defining point in evolution back in warmer climates. (We also sweat more efficiently) Perhaps this ability was still necessary much of the year when humans moved to more temperate climates.
Is it not also the case (perhaps I should say “theorized”) that lack of body hair is associated with a reduced parasitic load?
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The slightly softer-haired ancestor was slightly more attractive to the opposite sex, slightly more likely to have offspring and pass those softer haired genes along. That’s one way, rinse and repeat of eons. Very simplistic but retained traits are generally things that made it enabled it just a little more likely to A. survive and B. reproduce.
Of course there are other traits along with the hair that might have been the determining factor and it just so happened that softer hair genes were associated with the other genes more so than the genes that didnt get passed down and eventually died out and were associated with rough hair.
That makes sense I guess. There are just so many mysteries associated with evolution.
Remember that a trait doesn’t have to be bad to not be selected for. “Not terribly useful” is more than enough reason for it to disappear over many generations. When a trait is no longer being actively selected for, it’s going to fade away.
Yes, I was trying to get at this initially. There’s no automatic process for animals to develop more hair in colder climates. We don’t know if human ancestors ever had coarse protective hair in the past with genes that could have eventually led to a thick insulating layer of hair in colder environments. If they evolved in warm climates hair might have provided protection from the sun or maybe played a part in sexual attraction. We don’t know what genetic changes occurred in relation to the other changes that changed human form and function over time.
The real simple answer is that (proto-)humans with thicker and denser body hair did not reproduce more successfully than those with thinner and lighter body hair. Which brings up the question of why is that the case.
This is a possibility. Thicker hair may be an advantage in cold weather, but not enough to offset the disadvantage during hot weather.
Sometimes the answer is as simple as potential mates find the hair unattractive. It won’t matter how much of an advantage it is in surviving the cold, if thick haired individuals are still unable to reproduce.
This is always a problem with evolution. Sometimes the answer can be that biology and evolution aren’t perfect, and fail to select the most optimal traits.
Yes, if Ogg collapses of heat stroke chasing gazelles before Grogg does, that’s a survival advantage for Grogg… and the mighty hunter probably gets the girl(s).
Also remember, every evolutionary trait has a cost. Producing a full pelt requires more food. Bigger muscles or faster legs need more food. Size needs more food. Our bodies are a trade-off between what food was normally available and what was needed for survival.
Or not. As long as a trait doesn’t negatively affect survival, it can get passed along and change until some other useful purpose for it emerges.
A small extra flap of skin may serve no real purpose at first, but if it happens to grow larger it can help to dissipate heat, then it becomes useful for swimming farther, then gliding through the air, and eventually flying.
Or, as I put it in this old thread, “Why Blue Eyes?”
Getting laid? that’s the only reason the mutation has survived?
Umm, which early homo species that migrated to cold climates?
I might be wrong but I was under the impression that the Homo species that migrated out of Africa to colder climates didn’t need to get furry again for the reasons that Telemark already mentioned.
I’d have guessed that whoever gathered was more likely to be out in bad weather than whoever hunted. The prey are hiding from the bad weather, too. And you don’t hunt every day, so why not do it when it’s nice. You DO gather most every day, and the plants are still sitting there in the rain. And on the flip side, if it’s hot, whoever hunts has more need to shed heat than whoever gathers.
I think the link between testosterone and more hair has to do with growing a mane and sexual differentiation, and not with anything to do with collecting calories or dissipating heat.
H. erectus is perhaps the first to do so. They first migrated to southern parts of Asia 2-1.8 million years ago, but didn’t move to colder areas (China, Europe) until about a million years later. Erectus was the ancestor, via different paths, to humans, Neaderthals, and Denisovans.