Why are some people hairier
Why do you grow old hair on your ears and nose?
Sometimes more, sometimes less: testosterone controls hair growth depending on the part of the body
The issue mainly affects men. Many wonder about the contradiction that the hair on the head is decreasing and the hair growth is increasing on other parts of the body.
The dermatologist Gerhard-Alfons Lutz explains that two factors play a role: the hormonal balance and the genetic programming of the hair follicle cells. Hormones primarily mean testosterone, because it has different effects on different parts of the skin: The skin cells on the head are programmed in such a way that testosterone causes hair to fall out, while in the rest of the body testosterone leads to increased hair growth. This means that testosterone has a growth-inhibiting function on the head, whereas it has a growth-promoting function in the nose, between the eyebrows or on the chest, back and stomach.
Hereditary: reaction of the hair roots to testosterone
This is how boys get their body and pubic hair during puberty because testosterone stimulates hair growth all over their bodies. At the same time, some young men’s hair starts to thin out in their early 20s - it sounds contradicting, but both are a result of testosterone. How strongly the hair roots react to testosterone - in one direction or the other - is very much hereditary.
Bald head: When the hair stops growing back
There is a US study that has shown how baldness occurs. Baldness does not come about because hair falls out - they do that regularly anyway - but because it no longer grows back. And that in turn is apparently because - at least that is what the study found - that the corresponding stem cells in the scalp do not develop any further. That is, there are stem cells in the scalp that normally develop and specialize into hair follicle cells. But sometimes they don't; then the cells remain in their immature stem cell stage and do not develop any further. But why this is so, that stem cells do not mature any further, has not yet been clarified.
Evolution: Not every development brings a survival advantage
But why has nature arranged it in such a way that men on the one hand go bald, but on the other hand the body hair thickens? Nobody could tell me that, even at the Max Planck Institute for Evolutionary Anthropology they had no explanation for it. The increasing body hair growth is probably more of a concomitant phenomenon. So simply the continuation of what happens very quickly during puberty under the influence of testosterone - namely that hair suddenly grows stronger all over the body. It doesn't stop, it just goes on at a slower pace and doesn't bother you otherwise.
It is often the case in evolution that certain phenomena do not have to be explained by saying that they bring an immediate survival advantage. Rather, some things can develop in evolution that arise as a side effect of something else, as long as it does not interfere further or does not impair survival and reproduction. This also includes hair on the back or on the ears as well as Theo Waigel's famous thick eyebrows - they have never killed a man, let alone prevented them from having children. And that's what evolution is all about.
The text and audio of this post are licensed under the CC BY-NC-ND 4.0 Creative Commons license.
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