You can’t really say that the end of the wrist gets hugely more sunlight than the base of the palm:
And back to chimps and gorillas, their palms are jet black, and those aren’t exposed to intense sunlight that human ancestors were not. (And are thick and leathery to boot.)
I certainly get more photo-stimulation of my hands (and wrists) than of my inner thighs.
There is a book called From Hand to Mouth by Michael Corballis that makes an interesting case that gestural language preceded spoken language. He speculates (and it is hard to see what kind of hard evidence could be provided) that gestural language came first, got complicated, led to evolution of the language areas of the brain and then was supplemented and eventually taken over by spoken language. Among the rather thin pieces of evidence is how people with no language in common (or deaf people) will almost automatically to gestures to try to get something across.
Hey, that’s what I was going to say! Ninja’d! Dammit.
[quote=“Darren_Garrison, post:9, topic:939622, full:true”]
And, the “thicker skin” answer is factually incorrect–people have five times fewer melanocytes on their palms and soles, and nobody knows why:
[/quote]Just speculation, but it would seem that evolving any type of specialized cell (like melanocytes) would take more energy. And if that cell isn’t needed in that area of the body (does not produce an evolutionary advantage), than producing it is just wasted energy. So the individuals that don’t produce it have the slight evolutionary advantage of less wasted energy, thus gaining over thousands of years.
Ascribing a why to a feature may be pretty much impossible. Mutations that persist may persist for no other reason than that there was nothing selecting against them. My favourite example is vitamin-C. We have a doubly broken gene for vitamin-C. It is very unlikely that there is any selective pressure to favour a bust vitamin-C gene. But the theory is that the first disabling mutation occurred when our ancestors were living in an area where vitamin-C was replete in their diet. So the mutation spread unopposed through their descendants, all the way to us, simply because nothing selected against it. If the first mutation had appeared when vitamin-C was scare in the diet, the mutation would have been selected against heavily and never got out into the gene pool as a whole. Sadly a mutation to fix the busted gene is vastly less likely to occur, so even in the face of selective pressure, nothing good is likely to happen, indeed, so far all we have got is another mutation that busts the already busted gene again.
I have always wondered whether the creation of fingerprint patterns is in some way in competition with melanocytes. One notes that the lack of colouring is not just a total lack over the entire palm or sole, but in skin creases there is some colour. These are the bits of the hands and feet where there are no fingerprint like ridges. Perhaps it is as simple as the signalling mechanisms to promote creation of fingerprint ridges has the side effect of limiting melanocyte migration. That at least is something that could be experimentally tested for. Such a limiting could be quite coincidental, and not even absolute in effect. With no selective pressure against it, the effect would persist with no other reasons required.
That stock image certainly seems supportive of the gesture hypothesis, because the color contrast makes it much easier to see and distinguish between those gestures. Any such advantage is lost, of course, in people with uniformly pale skin, but pale skin is something that arose long after language.
You probably already know this, but that isn’t a specifically human/hominid break but one that happened more than 60 million years ago. (And there actually are hypothesii that it is an advantageous adaptation.)
Pale palms, on the other hand (okay, on both hands) is a human thing. Whyever it happened, it happened after humans split from chimps. And chimps (and gorillas) have fingerprints on their black hands.
I think this exemplifies the problem. They are still little more than just-so stories. There seems to be a headlong rush to find reasons for everything. But there isn’t the justification. It starts to become a Darwinian version of intelligent design. One needs to accept that some things are just random. Not everything happens for a reason and not every mutation has been selected for.
Unless there is some further evidence as to the extent of the selective pressure much of this is just noise that gets publication counts up.
Without wanting to start another round of debate about advantageous adaptation, my first thought in reading through this thread was that a feature or accidental side effect of having pale palms and soles is that finding and dealing with thorns, splinters, and insect stingers may be a bit easier in those areas. However, if that was a reason for adaptation, our fellow great apes are also tool-users (to some extent) with color vision and sensitive palms and soles, and it would make just as much sense for them to have this trait. Humans may well need to scratch and pick foreign objects out of their extremities much less often than other great apes, due to our lifestyles. Therefore, I am not proposing there is any rhyme or reason to it, just noting something handy (no pun intended) about it.
Well, here’s an alternative:
One of the traits of domesticated animals is a tendency towards white patches of fur/skin - you can see this with canines, where domestic dogs are far more likely to have white patches of fur on their face, their chest, and their paws than wild canines are. This also applies to cats and horses and domesticated foxes.
No one knows why these white/light color patches are associated with domestication and tameness, but they are in more than one mammal lineage. It certainly might be a case where the paleness is not what’s important but something else linked to pigment development that is also linked to a less visible trait important for domestication/sociability.
Perhaps humans are “self domesticated” - less aggressive towards others, more docile, more social, etc. and, like other domesticated animals, this made it more likely for them to have pale patches on their extremities which later became fixed as pale palms and soles.
Certainly, there are other primates that have uniformly dark skin on their paws/hands so it’s not a primal primate traits.
In the interests of fighting ignorance: The quoted word doesn’t make any sort of sense by either Greek or Latin grammar rules. The plural of “hypothesis” is “hypotheses”.
That is all.
Sure it is.
I never miss an opportunity to add a fake ii ending to a word whenever possible. If you want to think I’m lying about that, then I have no response to you that goes outside the pit.
If you feel that strongly about your little “joke”, then go nuts man.
Let’s drop the hijack.