Link #122: Humans Are the Only Primates Without Palm Pigmentation


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Link #122: Humans Are the Only Primates Without Palm Pigmentation

Image credit: nate steiner/CC BY 2.0

In our last article, we spoke about how you can get addicted to information. In fact, this isn’t something that is only limited to humans. Instead, it is something that can affect all primates because the experiment proving information addiction involved Rhesus monkeys.

This isn’t surprising because humans are very similar to other primate species. However, this doesn’t mean that they’re similar in every way because humans are very unique when compared to other animals on the planet. For instance, did you know that humans are the only primate species with no palm pigmentation?

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Why Don’t Human Palms Have Pigmentation?

Early humans.
Early humans. Image credit: Orin Zebest/ CC BY 2.0

It is true that humans are the only primates in the world that don’t have any pigmentation on their palms. Even if you notice darker skinned people like Africans and Asians, you’ll find that their palms are of a lighter colour than their overall complexion.

Their darker complexion is a result of melanin which is a pigment produced by melanocytes. According to scientists, in the early stages of their evolution, all humans had fair skin as they lived inside forests.

They had lighter skin because they didn’t need to deal with a lot of sun under the trees. However, as population grew and food became scarcer, more and more humans had to move out from under the trees.

The humans that had slightly darker skin could move outside the forest cover and forage before they had to move back in to avoid the heat. This allowed them to survive longer and pass their genes more. So humans with darker skin started showing up.

Because the human palms weren’t exposed to the sun as much as the rest of the body, they didn’t develop melanocytes as much as other portions of the skin.

Is There a Scientific Reason for Lack of Pigmentation in Human Palms?

Fibroblasts in cell culture
Fibroblasts in cell culture. Author: SubtleGuest?GFDL.

There’s a scientific reason for lack of pigmentation in human palms too. According to scientists, the palm region of the human hand and the sole of the human feet both have an excess of a certain type of skin cell.

This skin cell is known as a fibroblast. It is responsible for creating a specific type of protein called DKK 1 or dickkopf 1. It is this protein that is believed to cause the lack of pigmentation in the outer layer of the skin in human palms and soles.

How does DKK 1 achieve this? It does this by suppressing melanocytes. When melanocytes get suppressed, they’re unable to produce melanin. In addition to suppressing melanocytes’ ability to produce melanin, DKK 1 also prevents the pigment from travelling to its target skin cells.

This isn’t the only effect of DKK 1 on the human palm. Have you ever wondered about your palms’ and soles’ skin being thicker than your skin elsewhere? This is also caused by the DKK 1 protein.

DKK 1 is proven to affect three genes in the human body. These are β-catenin, αKLEIP, and keratin 9. These genes combine to make the skin in the palms of your hand and soles of your feet thicker so that they can withstand the heavy use that you put them through.

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