We are hairless because we are neotenous apes. It didn’t evolve “for” any particular reason or function, nor did it evolve independently from our other traits (that is, humans as a biological entity did not start off hairy and evolve hairlessness as an adaptation). Just as an FYI.
Or is this just a path to adaption? If hairlessness is a phase we grow out of, when some genetic characteristic expresses itself - then if hairlessness becomes an advantage at some point, then delayed or failed expression of the the “hairy” gene is a plus and spreads as a species characteristic.
That explains my nostril and ear hair later in life.
… and mature males grow a thick pelt across their back and shoulders to allow the younger members of the troop something to hang on to while travelling.
Fashioned stone tools. Chimps use lots of tools, so it’s likely our common ancestors of ~6M years ago did, too. And Chimps use some stone tools, too. They just don’t modify stones for use at tools, but they do modify wood for use as tools.
I agree that the answer to this is “none”.
Not sure I buy that, DF. We certainly have many neotenous ape features, but:
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Is “hairlessness” one of them? We have as many hairs as our ape cousins, but most of them are very short. Is “having short hair that stays short” a neotenous trait?
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We really have no way of knowing the answer, and whatever answer is put forward is nothing more than a hypothesis, right? A hypothesis that I don’t think we could even test today, although we might be able to do so in the future.
Tell that to the Neanderthals.
“Hairlessness” is, of course, not a very accurate description of our condition - certainly we have hair, it just isn’t as long as in our relatives. But I would also say that our hair doesn’t “stay short”. As I noted 9 years ago (!), we tend to get hairier as we age (I can’t help but notice that I am hairier still than I was when I wrote that post…). Who knows, were we to extend our lives out to a few hundred years, we may find our coats to be nearly as full as those of other great apes.
It’s also possible we may never know “The Truth”, but certainly neoteny as a hypothesis makes testable predictions, so we could at least determine how well neoteny fits the evidence vs other hypotheses (e.g., treating relative loss of hair as an adaptive trait in and of itself). From what I’ve read over the years, the neoteny hypothesis does just that (as well as explain various other human traits, such as our large brains).
Just want to point something out. If we suddenly reverted to the stone age, lots of people would die because technology keeps them alive. The genes that leave them unable to survive without technology, the technology is usually modern medicine, will still survive in generations to come, so lots of people will die for many generations who would have been selected out if we didn’t have millenia of technology before. But I don’t think all, or very many, of the genetic material that allowed us to survive before technology are gone. Humans without technology would still survive as long there were sufficient resources. And of course, unless they lost some brain genes, technology would spring back up again.
My point is that technology has created greater diversity among humans, but hasn’t evolved us to the point where we’re no longer able to survive without it.
This seems to me to be unnecessarily pedantic, and more misleading than helpful (if not downright inaccurate). To be sure, traits, such as hairlessness, do not appear in order to meet some adaptive need, but (generally speaking) they only stick around and spread through a population if they do serve some adaptive function. That is what people mean when they talk about some trait evolving, and it makes perfectly good sense, then, to say that the trait evolved (emerged and was then selected for) because it served some function.
So yes, humans (or the ancestors of humans) did start of as hairy (as adults), and then evolve hairlessness (as adults) as an adaptation, and whether or not neoteny was involved in the original emergence of the trait is beside the point. The concept of the process of evolving something (in the context of modern evolutionary theory) involves the concept of that something being selected for over the generations.
I disagree that it is either pedantic or inaccurate. Organisms are not simply the accumulation of traits, each of which is selected for independently. There are a good many constraints for many traits; many traits are indelibly linked with others. It is a misconception that traits only stick around if they are advantageous. They may be completely neutral, or even deleterious, but linked to other traits which are advantageous, and thus stick around. I do not agree that Adaptationism (as a school of thought) is accurate for describing all evolutionary processes.
And, of course, my whole point in mentioning this in the first place was to counter the idea that hairlessness had been selected for. I have not seen any evidence that such was the case and it is more likely a pleiotropic effect of our neotenous development being selected for.
But the basic concept/argument is that we evolved (selected for) (relative) hairlessness because it aided significantly in the sweat / heat shedding process for our primary hunting mechanism, running. the hypothesis then is that this was more important and useful than the balancing benefits of having body fur, at least in the African climate.
Note too that the people still local to this climate retain (or developed) an interesting adaption to maintain the balance between scalp hair and ventilation for cooling - their scalp has very curly or kinked hair to allow more airflow than other branches of homo sapiens typically display. (Suggesting the hypothesis that those who left Africa eventually found the heat and protective value of flat head fur more useful than the open, fuzzy variety?)
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I suspect it may well have been the other way 'round: humans were able to become long-distance hunters/runners because of our relative hairlessness and bipedal stance, all of which evolved pretty much simultaneously, again in keeping with a hypothesized neotenous origin; something as “simple” as altering timing during development had the effects of changing our fur coat, stance, brain size, and so on. And all of that, in turn, would lead to changes in physiology, allowing for greater stamina, etc. Note that we pretty much had to have the whole tool-using thing down before we could start running down prey, which means we were probably already less hairy and more upright by that time.
Maybe, maybe not. If we could run down a four-legged animal to the point of its exhaustion, an un-shaped rock would suffice to stop it running any further… And then there would be the frustrating tearing at the thing with progressively sharper rock shards to discover how to cut flesh… A new food source is probably a good motivator to develop the proper tools.
Again, we can speculate all we want with these Just-So Stories. I guess the real question is, why are the apes and chimps so hairy then? Like pig-types, and several other species (which I’m sure I’ll remember later) relative hairlessness is not unknown in mammals when the climate allows it; and still prominent when you would think the climate would contra-indicate it.
At least no one has referenced the Aquatic Ape “theory”.
I just wish someone would figure out why men get bald, and then fix it, goddammit! Insult to injury-- as we age, we get hair where we don’t want it and lose hair where we do want it.
I let my nose hair grow out and comb it over my head.
That wasn’t what I was talking about. I was pointing out that if many apes prefer cooked food, there’s no reason to assume that we have a taste for cooked food because of technology and not for whatever reason they like it.
If we are less hairy so we can run then presumably the answer is that other apes don’t run. Not in the same way, anyway. And they, of course, don’t make clothes or even blankets. Don’t pigs use mud as protection from the sun? They’re quite bulky animals so presumably lose heat fairly slowly and don’t need hairs much for warmth. In more temperate places they have more hair. As for why the same thing doesn’t apply to apes, maybe they live in places that get colder overnight, and they’re less bulky anyway. My speculation is getting pretty weak now. But it’s interesting.
Humans sweat differently from pigs(and most mammals). That is why your dog pants: he is shedding heat through respiration, since he cant soak his fur with sweat. They cant do it very well when running.
And that allowed prehistoric humans to run down animals. Its called persistence hunting.
As the animal heated up, its muscles would cramp and build up with lactic acid, inhibiting its ability to flee, and causing physiological problems. At that point, the real chase was on, and the (proto)-humans could possibly take a last big gulp of water, flushing their systems.
They would charge! The animal would panic. Its adrenaline would soar, but its thirsty, hot and tired. Internally everything was all wrong for fleeing.
The prey would run, but could only hobble at a fraction of full speed. Eventually, like an un-oiled machine everything would seize up. Their muscles would cramp, they would trip and stumble. Eventually they would fall down, perhaps breaking bones, tearing muscles and cartilage.
The (humans) would swarm it, stabbing it with their spears.
There are select people in Africa that still hunt this way.
You can hunt just about any animal this way. Never let it stop for a rest.
That is why wimpy little humans were the apex predators.
Yes, the human sweat system is remarkable.
Like most evolutionary traits, there is no chicken vs. egg situation. Darwin’s finches did not suddely pop out omlettes with the right shape of beak - those with a bit of an advantage in beak shape were better at popping open nuts or crunching insects while thier peers starved. More pronounced beak shapes, and the evolutionary desire to seek out like-beaked(?) mates, probably came with time.
Similarly with humans, hairs, running, and tools, I assume. As we learned to usewhat we had, the better ones got fed and the lesser ones did not. I’m sure a modern kenyan runner, with or without Nikes, could out-do 4-foot-tall Lucy in a race to the wildebeast any day… but the early humans did not have to compete with Hussein Bolt types, they did not even have to be able to run down the healthiest adults in a herd… They just had to be smart enough to pick out the least capable from the herd, and sufficiently numerous that when the thing decided to turn and charge or fight, there were cohorts that could take it from the side. Notice that these activities encouraged smartness and cooperative behaviour.
Plus, the most agile bipeds with the best ability to shed heat thanks to being sweaty and less hairy, were usually still with the pack when the kill and feeding happened… and also these “mighty hunters” would get the girl more often than the nerdy hairy slow australopithecus with glasses… thus selcting for the successful traits.
Again, more just-so stories, just not Kipling.