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Body hair helps to thermoregulate.
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Your scalp protects your scalp from the beating sun, but it also captures heat if you are in a cold weather.
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Eyelashes are like screen doors for the eyes, which keep insects and dust and small particles from debris whenever they are opened.
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Eyebrows prevent perspiration from entering your eyes.
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Axillary hair, technically called “axillary” hair, collects and disseminates pheromones acting as WD-40 on body hair, reducing friction between the skin on the lower arm and the skin on the side of the chest as we walk and swing.
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Pubic hair also helps reduce friction, as well as provides a protective layer against bacteria and other pathogens.
What about facial hair? You will notice that it does not appear on the handy list of adaptive hairy features.
In the early days of studying this type of thing, evolutionary biologists thought it could serve thermoregulatory or prophylactic purposes similar to body hair and pubic hair. The beard and mustache are around the mouth, after all, and the mouth receives food and other particles that could lead to disease. The beards and mustaches are also on the face, which is connected to the head, which loses a lot of heat from the tip if it is not covered by hair. Everything makes sense when you look at it that way.
Except that there is a problem with this theory: it excludes 50% of the population, ie FEMALES. Natural selection is ruthless and has sent MANY species through the dodo – for example, the dodo – but rarely, if ever, selects for a trait in such a species and leaves half the population hanging, especially the half that makes all babies ( that is, the most important half). If facial hair were meant to perform important functions, it would be present in both sexes. Instead, the thick, mature hair of the face is present almost exclusively on the male half of the species, and its only task is to stand there on the face of its wearer as a signal to all who cross its path.
What a signal it makes facial hair send? Well, here it gets a little complicated, as the ornamental features go. Professor Geoffrey Miller of the University of New Mexico, one of the foremost evolutionary psychologists in the field, put it this way: “The two main explanations for male hair are intersex attraction (attracting women) and intrasexual competition (intimidating rival men).” Basically, facial hair signals one thing to potential partners (namely virility and sexual maturity, hubba-hubba things) and something else to potential rivals (formidable and wisdom or piety). Taken together, these signals give their own high status mark to men with the most majestic mustaches or the largest and bloodiest beards.
The signal that facial hair sends also tends to be stronger and more reliable between men, who are more often rivals, than it is between men and women, who are more often partners. In fact, evolutionary biologists will tell you (if you ask them) that while some women like facial hair very much and others don’t like it and others don’t care less, most often the attraction is just as much. dealing with beard density like anything else. That is, if you are in a place where there is a lot of beard – say, a forester convention – then a shaved face is more attractive, but if you are surrounded by bare faces, then the beard is best.
In evolutionary genetics, this is called “negative frequency dependence” (NFD), which is a scientific word for the idea that when a trait is rare in a population it tends to have an advantage. In guppi, for example, males with a unique combination of colored spots mate more often and are less preyed upon. This is a huge competitive advantage. It’s like going to Vegas, waiting to lose $ 1,000, but hoping to draw, to win $ 1,000 instead. It’s a $ 2,000 swing! It is the same for a feature with NFD selection. The trait goes from fighting for his life to being the life of the party. The downside is that the competitive advantage can lead to overcrowding with others with the same trait very quickly, due to everything that makes the guppy look very interesting – which means it loses its rarity and becomes commonplace. Don’t worry, nature has a solution for this: as more guppies wear the same trait, it leads to a decrease in interest from colleagues and an increase in attention from predators. What was once the new hot thing with guppy becomes old news, in other words.