Our hairlessness has become a source of what we think of as beauty, a reality validated in every National Enquirer article about a “wolf boy”. It also has widespread consequences for our health and quality of life. It is the reason for the origin of melanin (the compound that, when present, makes dark skin) in sunny regions. The production of melanin in cells is just under the surface of the skin evolved in Africa, along with our loss of hair. All of our ancestors produced melanin and so were dark skinned, but when some of our ancestors moved out of hot climates, melanin blocked too much sun. At least a little sun on the skin is necessary for our bodies to produce vitamin D. Dark-skinned individuals in sunless places suffered rickets. The died, and so, with time, pale-skinned genes were favored, not just once but several times independently, with the northward migrations of humans. In other words, the variety in our skin color would not exist were our skin not exposed in the first place by our lack of hair.
- Rob Dunn, from The Wild Life Of Our Bodies
This leads to several questions for me:
1. Were the first humans black, brown or white (underneath their fur)? Or were they kind of grey coloured, like our Border collie when he’s clean shaven. (Not that I have done this.)
2. Don’t furry animals need Vitamin D, too? Where does our dog get his vitamin D from, since he’s covered in hair?
According to this Vitamin D Wiki, they do. So how do they get it when they’re covered in fur/feathers?
NOTES FROM THE PODCAST
Human skin is not much different in its basic structure from the skin of other animals walking around. But other mammals tend to be covered in hair, so it looks quite different. For most of our bodies we are functionally hairless. This makes us very sweaty. That is extremely important to the human economy.
The next uniqueness is that human skin comes in a variety of natural colours. This is unique to our species.
The last unique feature of human skin is that compared to other animals we actually do things to our skin. We decorate it and use it as a canvas for self expression. Makeup, tattoos, piercings have great social significance.
Nakedness and sweatiness go together. In the course of evolution of our lineage, skin is hard to learn about because skin cannot be preserved. Nevertheless we have good evidence and we know we’ve had naked skin for a long time. This has been necessary for us to be more efficient sweaters. Humans and other primates are excellent at losing body heat through sweat. Your typical dog pants to lose heat. A sheep loses heat through a mechanism at the base of its brain which allows it to cool a lot of blood flowing through the brain in particular via its nose. The more active the primate the more numerous its sweat glands. We come from a type of ape that has a moderate number of sweat glands. Other apes were extremely energetic in their activity, similar to modern humans so they must have had the ability to cool themselves with sweat glands. We had excellent sweat glands since 2 million years ago.
When a horse sweats a lot they actually lose their ability to keep cool because their hair becomes compressed and their ability to lose heat through evaporation is limited. So the more hair you lose the more cool you can become by sweating. This is why we became hairless.
The ancestral form of our lineage living only in equatorial Africa (2 million years ago).
Hairless skin without pigment is very subject to burning. Recently we’ve become very aware of the sun but before that people didn’t protect ourselves well from the sun. Before that unpigmented skin burned a lot. This damage is not just the kind that causes you to have wrinkles and have skin cancer when you’re older but is actually damaging the DNA in your body essential for normal health and reproduction. So all of a sudden sun doesn’t become a little bit bad for you but a positive liabiliy.
It was at this time in our evolutionary history that our species became darkly pigmented. All of us around 2 million years ago were darkly pigmented. The story of skin pigmentation then really starts out at this common denominator and it becomes interesting as the population disperses. This occurred quite quickly and we have humans going into Eastern and central Asia then Europe over the next million or so years.
When people go into these places their skin colour underwent major changes. Pigment in skin not only protects against dangerous effects of ultraviolet radiation but also is to do with making Vitamin D. Evolution is happening in our skin all the time. The pigment is filtering out a certain amount of radiation but also allowing a little bit in so that you can make vitamin D. Organisms like humans are remarkable in that through the course of natural selection we’ve tinkered with the amount of pigmentation in skin exactly right.
Outside the tropics, where humans first evolved, there isn’t very much of the UV radiation that makes vitamin D, and yet we need vitamin D to be healthy. That’s why, as humans moved into higher latitudes lost pigmentation and that’s why many of us have lightly pigmented skin, especially of northern Europe and a few from northern Asia. This pigment (melanin) can be produced temporarily by people who tan. It was an important response that evolved in some people to deal with the increased UV that occurred for part of the year. (Summer)
We use skin constantly to advertise ourselves. Even for those who put no decoration on our skins, our skin tells a lot about your state of health. It immediately gives a signal to any observer about age, how much sun exposure you’ve had and what your likely ancestry is, even from 50 yards away.
If you have a certain amount of makeup on of a particular kind, or if you have tattoos of various kinds and positions I learn even more about you before you say anything. We use these cultural mechanisms to great advantage, to give people info about ourselves before they even talk to us. In modern society where speedy social interactions are the rule rather than exception more and more people are relying on this kind of advertising. (eg black and white goths)
There’s a difference between cosmetics and something like a tattoo or piercing. Many older people can’t relate to tattoos as a visual medium and think it’s a foolish thing to do. After interviews, I realise young people think extremely carefully about it because they want a tattoo to be another symbol of themselves. Tattoos are not something people undertake frivolously. The vast majority consider it very carefully. It speaks of very deeply held aspirations about themselves, and have become extremely popular in the last 5 yo 10 years.
We use our skin to gather information about our environment through the sense of touch. A lot of animals do this but we use ours tremendously especially the tips of fingers and face. We use the sense of touch to gather a huge amount of info about our environment and about each other. Primates evolved to constantly touch one another. Humans also in a hunter gatherer society have a tremendous amount of physical touch between members, but our society has regulated against most of this kind of touch. If we were chimpanzees a roomful of students would be intertwined with one another, grooming. We tend to discount this part of our legacy. Touch is very important to normal childhood development and physiological well-being. Individuals in nursing homes do much better when they are touched and hugged. We prefer to communicate with each other via remote means eg internet, phone.
2. Surprising Siblings: Black and White Brothers Are Actually Twins shows that people of Caribbean descent often carry European DNA.
3. Some Doctors Aren’t Wild About Self Tanner And Prefer You Stay Pale from Jezebel.
4. And if this article doesn’t stop you from using sun beds nothing will, from Women’s Health.
5. Based On The Colour Of One’s Skin, in which we are cautioned against confusing skin colour and racial identity, from Zero At The Bone
7. The Enduring Popularity Of The Tan from The Beheld
9. Tanning Is a Young, White, Female Problem. And It’s Deadly, also from Jezebel.
10. Pigmentation: the simplest of complex traits not so simple? from Discover
11. Neanderthals Came In All Colours, Discover
12. For writers: Handy words for skin tones from Josh Roby