If were once apes, and we evolved to match our needs, like bigger feet to stand on our legs and so on.... why did humans start to grow long hair? what was the social or environmental need that made us evolve into needing long hair?
Why do humans have long hair on their head? monkeys don't.... what was the evolutionary need for it? Humans have a thicker neo-cortex in the brain, the layer of gray matter where thought and higher intelligence reside. Long hair would serve an insulation from extremes of cold and heat and have survival value for the most intelligent humans, especially until they had offspring. Teenagers lose a huge number of brain cells during the period their hormones are in upheaval and they are becoming adult. Therefore the brain needs special protection at least until it is finally stable. Just using my cortex.
Why do humans have long hair on their head? monkeys don't.... what was the evolutionary need for it? Seems like a difficult question...
I guess it has something to do with sexual selection. I don't know why we lost most of our hair in the first place, but long hair could evolve as a substitute for that. I mean, a strong and shiny fur is an indicator of good health, and may have been used by our ancestors in mate selection. A healthy partner is more likely to have good genes for our offspring. And as we lost our fur, we could grew long hair instead; in the first place, hair on the head was maybe kept as a protection from the sun, and it grew longer because it's easier to spot health in longer hair. Long shiny hair is more impressive than short shiny hair. I guess. Take this as speculation :)
Why do humans have long hair on their head? monkeys don't.... what was the evolutionary need for it? There is a contentious theory of evolution called the aquatic ape theory, it suggests that at some time in our past we went back into the sea, this would help to explain why our bodies are mostly naked, we distribute fat evenly all over and walk upright, noone of these are features shared by other land mammals.
There is a precedent... Dolphins and whales evolved to be mamals on land but then went back into the sea, perhaps our ancestors did as well, but stayed closer to the shores, hence standing upright and why hair on our heads would be retained in order to protect the only part of the body that was almost constantly exposed to the sun.
Another support of this is the swimming new born baby effect, a new born child can orient its self in water and move a small amount, on land it just kinda lies there, the offspring of all land mamals can move themselves around a bit as soon as they are born (or shortly after) so why cant we?
there are a lot of other supporting arguments (but sadly no evidence) it is a theory I really like because of all the evolutionary oddities it answers, including why we still have hair on our heads but not the rest of our body.
Why do humans have long hair on their head? monkeys don't.... what was the evolutionary need for it? physcologists have shown that men prefer women with long hair so the sub concious desire for women to keep long hair as it looks more feminine has kept this gene in the DNA.
Why do humans have long hair on their head? monkeys don't.... what was the evolutionary need for it? Certainly, there are a number of theories for the differences in ape body types. I don't claim that this explanation is a dominant one, but perhaps it gives you some peace of mind. My explanations here are related to aquatic ape theory (AAT), which you can see in the source that I have listed below. Some other answers list some other support for how AAT answers your question. If you are interested in this idea, you should see the source listed below and note that there is very little fossil evidence for this theory.
(note: Human beings *ARE* apes. Apes are anything part of the superfamily Hominoidea of the order primate. Monkeys are NOT in this superfamily; however, humans, gorillas, chimpanzees, and orangutans all ARE in this superfamily. Those four are known as the "great apes." See the second source for more information about human genetics. Note, of course, that the similarities among primates are due to a common ancestor of ALL primates. None of the currently living primates (including monkeys) "evolved from" any of the others. They all involved from one common ancestor)
(aside: when looking at a primate, except for a few exceptions (like the macaque monkey), it's generally easy to tell an ape from the rest: apes (e.g., humans and chimps and gorillas) don't have tails)
High selection pressures on large brain size in humans combined with selection pressures on walking upright have produced lots of interesting effects on the rest of the human body. Human females need strong hips to allow them to walk upright. However, this will prevent birthing children with large heads. The result is that human beings develop far less than other apes within the womb. This is why a 2 year old human baby is at a similar stage in development as an infant of other apes.
Additional factors slowed the development of ape features. This is why infants of other apes "look" like old humans.
Thus, processes that occur within the wombs of other apes (that may, for example setup for hair growth on the head which slows and then sets up hair growth elsewhere on the body) stop short in human beings. This may be why human beings appear hairless. We are removed from the womb earlier than other apes, so we may not complete the process that other apes complete to lay down new hair.
Additionally, there is probably some natural selective pressure on having hair on the head. For one, the thin and delicate skin surrounding the skull would be constantly bombarded by the sun and its thus needs protection from hair. Additionally, sweat from the head that would run down the face is absorbed partially by the hair. Not only that, but hair does provide SOME protection to the head from some trauma and some heat insulation. And finally, hair may provide some visual protection from predators (some eagles have been shown to prey on human babies by attacking the head and then waiting for the baby to die).
Finally, there may be some sexual selective pressure on hair. Those with longer hair may have appeared (for some reason) more attractive than those with shorter hair. Gradually (think of a male peacock and its extravagant displays) hair was picked up as a trait that would be desirable for those humans that wished to reproduce.
These types of questions are hard to give concrete answers to. All we can do is speculate.
However, there may not be any NEED for hair. Not everything is the product of selection. In fact, selection REQUIRES that some variables be allowed to float. This allows selection to put pressure on other things (for example, brain size) and let those things without selection pressure to vary. Sometimes those variances provide the freedom needed to put the selection on more "important" traits.
Something else to consider... Why do male mammals have nipples? There is no need for them. However, there is not much selective pressure to get rid of them. There is certainly a cost to producing them. However, that cost is either not that great (comparable to the cost of producing skin in their place, for example) or comes with a great benefit (it may be efficient to put nipples on males because that allows for placing nipples on females, which do have a function). Hair may be something similar. It may just be hanging around because it doesn't seem to have much of an impact (and losing it may force us to lose something more important, like hair under the arm pits, which does have a function).
In other words, keep in mind that you shouldn't ask WHY we have things. You should ask why having them (or not having something else) would give an advantage over some other option. It may be that we're hairless because being born earlier and having slower hair development provided an advantage, and then having hair on our head provided additional advantage from protection from the sun (because we're bipedal). Thus, if the head hair developed later, it may have been formed from completely different pressures than the hair you see on other apes. Thus, it takes a different shape and size.
Why do humans have long hair on their head? monkeys don't.... what was the evolutionary need for it? 1) we weren't apes, we shared a common ancestor
2) you've just described lamarkism, which is false. its like saying giraffes grew long necks because they needed reach the top of the trees.
Why do humans have long hair on their head? monkeys don't.... what was the evolutionary need for it? The organ with the hardest job is situated in your head. By evolving, you have given it even more importance and so it grew to be the rational central unit of your body. Because the protection lairs are so thin, they do not shelter as well as thy should, so, by the law of compensation, hair grew longer and stronger on man's head, to protect the brain from cold and sun. Monkeys spend their time in trees and they usually live in warm areas. Primates that do coupe with bad weather or spend a lot of time in the sun have sufficiently big hair on their head.
Why do humans have long hair on their head? monkeys don't.... what was the evolutionary need for it? The reason we have hair on our heads at all is believed to protect our head from the sun. Because we stand up right on two legs and not horizontal on four legs like most other animals (including apes), our heads (and not our backs) are the most vulnerable to direct sun rays. The hair on our heads protects our skulls (and therefore the brain) from intense heat from the sun, and it keeps our heads warmer in winter. Since humans walk upright, the only other part of our body that would be vulnerable to the elements would be our shoulders as the extend outwards further than our heads. Long hair would, in theory, offer some form of protection from the sun to this area.
