True, but people have been in the Americas long enough for a gradient of skin colors to develop, with the darkest in tropical areas and the lightest in the Arctic.
As mentioned, peppercorn or kinky hair seems to have been present in the earliest lineages of modern humans to migrate out of Africa (Andamanese, Negrito, some but not most Australoid). The initial migration seems to have been through tropical South Asia. If it were highly environmentally adaptive, one would think that it would have been selected for in later populations living in this area. These have anything from coarse straight to curly hair.
Of course, they are not directed to give the organism some advantage but they are not totally random either; with some preferential sites.
Sort of like your bowl example - except the bowl is not smooth. It has furrows/channels on it and thus limits the number of directions the marble can take.
AIUI too, tightly curled hair stops sun heat from overheating the scalp, makes sweat easier to evaporate rather than soaking the hair (and transferring the sun’s surface heating of the hair to the scalp; I know back when I had hair (straight hair) it could get very hot in the sun. Curly hair allows for air flow to help cool.
The first flow of modern(ish) humans out of Africa as far as Australia seems to have been the darker skinned, curly haired variety. The type that moved to central Asia seems to have completely lost any ability to have curled hair. (Although it is an occasional trait in Europe.) The short answer then is that China, Siberia, and then those who moved to the Americas all had straight hair. Evolution has apparently had time to change that. Another mitigating factor may be that by the time migrants made it to tropical America, they had the ability to make hats. Plus, unlike south Sahara, they possibly had lesser temperature extremes and more cloud cover in most environments, so less incentive for (selection for) the curly trait.
Whereas skin darkness has an immediate and rapid effect - those in sunny climates are personally better protected from skin cancer with more melanin. The strong selection criteria is evident.
Technically there are no humans native to the americas.
They all came across from somewhere in asia/siberia.
For them to change much from how they came over, there would need to be a catalyst
to trigger mutation, apparently there was none or perhaps they had become smart enough to mitigate any catalyst?
Plus there were not here very long i suppose one might say.
This is a pointless nitpick, since it’s obvious that the reference was to people who were in the Americas before the arrival of Europeans about 500 years ago, and having been here for more than 15,000 years they were “native” compared to them. This is a much longer time than it took for blonde hair and pale skin to spread in Europe. The gene for blonde hair in Europe seems to have originated evolved about 11,000 years ago, while pale skin had not yet spread to parts of Europe before 7,000 years ago. Native Americans had enough time to show local adaptation.
There is no reason whatsoever that the background rate for mutations should be different in the Americas than anywhere else on Earth. I have no idea what you mean by “smart enough to mitigate any catalyst.”
Interesting topic. I have some tangential questions:
Pubic hair is always black and curly. I think this is universal (can it be confirmed?). I would guess functionally it provides similar cooling properties as discussed above, plus, uh, cushion, and perhaps a dry form of lubrication.
Similarly, armpit hair seems universally black and straight. I presume it’s that way for cooling and dry lubrication as well, but not so much need for the cushioning.
Maybe my assumptions are not correct?
I suppose conditions in those areas have not changed all that much over the course of human evolution, so not many changes in hair type there. If scalp hair faced similar constants, I would think we would not see such a variation in hair types. Is this due to the invention of hats? Why is head hair so varied while other parts of the body the hair seems more constant?
Also, are there any known human groups lacking in armpit hair and/or pubic hair? Please hold the wise cracks about porn.
My extensive field research on this topic shows that this is not the case. It can be blonde or red, and it can also be essentially straight. As the saying goes, usually “the carpet matches the drapes,” but pubic hair is often a bit darker than head hair.
Well not always, in either case. I recall being briefly thrown off by public hair that was indeed black, but had a texture I can only describe as “baby hair”; that is, straight, very fine, and oddly soft.
Interesting, too, in that men’s beards are public and they sometimes are a different color than their head hair. Mine is like that. Head hair is brown (with maybe a rare bit of red in a few places), but my beard hair has lots of red in it among the brown hairs. Of course most of my beard hair is grey these days, but in my younger days the red was pretty noticeable whenever I grew a beard.
Three things I, for one, found interesting in the NSFW Wiki “Pubic hair” [ en. wikipedia. org slash wiki slash Pubic_hair] I dutifully went to consult:
“Patterns of pubic hair [are] known as the escutcheon.”
There is a reference standard on pubic-hair growth.
Like the Bourgeois Gentleman who was enchanted to learn he had been speaking prose his whole life, I, with the aid of a photograph, learned I had been looking at, more or less most of my life, an American Wax.
It can be blonde or red, and it can also be essentially straight. As the saying goes, usually “the carpet matches the drapes,” but pubic hair is often a bit darker than head hair.