okay, so, why is it that people with darker skin, lets say, african americans have light skinned palms …yet the rest of the their skin is dark?
Paging Eddie Murphy! Mister Eddie Murphy!!!
I think because the skin on the palms (and soles of the feet) is so thick that the pigment is not as dense.
At a guess: since melanin provides a certain amount of protection from direct rays of the sun, some distant mutation occurred that lessened melanin production in places that were never exposed to the sun for any length of time (palms, soles of feet) and that mutation was not selected against because no one died of sunburned soles.
That doesn’t explain why their taints are still dark though.
If the mutation did not occur for any other part of the body, then it will not manifest in any other part of the body. Evolution is not a directed process and Lamarck did not provide the correct theory for the majority of evolutionary events.
The reason may be along the same lines as why humans have no hair on their palms and soles. Maybe?
I think the answer may be a combination of a few of the ideas advanced by already by some of the posters in this thread.
The skin on the palms and soles (acral skin) is structurally and functionally different from other skin. The outer dead layer (stratum corneum) is MUCH thicker than in other areas. The pigmented cells (in the basal layer of the epidermis) are beneath the stratum corneum. Therefore that stratum corneum is in the right place (closer to the outside than the basal layer) to play some role in determining the underlying tone. What’s tough is that, a priori, why would one think that the underlying tone would appear lighter due to a thicker stratum corneum?
I’m unsure whether pigment density is different on palms and soles compared to non-acral skin. It’s not exactly the sort of research that wins Nobel prizes or big research grants, so I couldn’t find any articles addressing this issue.
I’ve observed something in patients that may give a clue to the ultimate answer, though. The palmar creases in dark-toned individuals appear more highly pigmented than the surrounding skin (perhaps approximating the tone in non-acral areas). Assuming that pigment density in the creases is similar to the surrounding skin (which could be a mistake), one can conclude that the arrangement of overlying epidermis (flat in non-fold areas, folded up in folds) greatly affects transmission of underlying tone. One might extend this idea to conclude that arrangement of the stratum corneum (thin, thick, folded) affects how underlying pigmentation is transmitted.
Choosy (budding dermatologist)
You know what’s weird? I’m a white person, and yet I have some dark spots on me and the skin under my eyes gets really dark sometimes!
Sorry. The OP sounded a teeny bit … unfriendly.
Meanwhile, I’m covered with hair. All over my body. Hair hair hair.
No human has pigmented palms or soles,its just that you don’t notice it in light skinned people since it blends in.
effac3d I call bullshit on that one. My palms are the same color as the rest of my body, and I’m no albino.
When I am not tanned, there is very little difference in the color of my feet as I go from the top of the foot to the bottom. When I have tanned deeply in summer (I wear sandals), the tops of my feet are darkly tanned except for where the sandal straps cover.
In traveling (visually) from the top of my foot down along the sides, the color doesn’t change much…and then there is a fairly sudden change in color at the beginnings of my soles…which have remained their typical pinky color. So my feet resemble the situation found in people who are highly pigmented.
Interestingly enough, a similar pattern exists on my hands…and the palms are exposed to the light!
I conclude that there are either far fewer melanocytes in the palmar and sole skin, or they don’t respond to light or perhaps the epidermis is too thick to show the darkening…(but the skin on the inside of my arches is quite thin, and still don’t tan even if they get sun).
So, effac3d, I think your observations are correct!
Just to add a random factoid to the mix, I have a freckle on my palm, right in the center of a non-creased part. Did my pigment layer only pop up in that one place or what?
Most likely it’s a mole and not a freckle. Moles on the palms and soles are fairly common and generally nothing to worry about. Most develop during childhood but normal moles continue to pop up until the mid-30’s. However if you begin to notice changes in it (enlarging, darkening, changing shape) I’d show it to a Doc
Moles are collections of normal melanocytes (the skin pigment producing cells) in the epidermis, the dermis, or both. I’d bet your mole is an intradermal or combined collection. The reason moles sometimes cause problems is that they harbor so many melanocytes, which are the precursor cells of melanoma.
I heard it was because they had their hands up against the wall while God spray-painted them.
Non-factual anwer follows. I heard this story told as a legend when I was growing up. I do not know it’s origin.
When the earth was young all people were dark skinned and lived in harmony. One day one of the people stumbled upon a large puddle in the forest. As it was a hot day he decided to refresh himself with a swim. When he came out of the puddle he found, much to his surprise, that the “water” had turned his skin almost completely white! He hurried back to the village to show the others. When the other people saw him they were most excited! Here was one who was now different from anyone else on earth. His difference set him apart and made him special. Wanting some of this “specialness” for themselves, all of the villagers ran to the puddle and jumped in. As word of the magic water spread, people came from all over the world to swim in the magic water. As more and more people swam in the puddle the magic water got more and more shallow until swimming was no longer posssible. People still came and rolled in the puddle, lightening their skin as much as possible. When the last people on earth to hear about the puddle finally arrived, there was only enough magic water left to pat their palms and the soles of their feet. This was the way that the people of the earth became different hues. To this day, many lighter skinned people continue to see themselves as special, since their ancesters were first to the puddle.
A pretty insightful legend, I think.