What was once the hot new guppy thing becomes old news, in other words. Not to worry, nature has a solution for that: As more guppies bear that same trait, it leads to a decrease in interest from mates and an increase in attention from predators. The downside is that the competitive advantage can result in overpopulation of others with the same trait very quickly, because of all the getting-it-on the very interesting-looking guppy does-which means it loses its rarity and becomes common. The trait goes from fighting for its life to being the life of the party. That’s a $2,000 swing! It’s the same thing for a trait with NFD selection. ![]() It’s like going to Vegas expecting to lose $1,000 but hoping to break even, only to end up winning $1,000 instead. In guppies, for example, males with a unique combination of colored spots mate more often and are preyed upon less. In evolutionary genetics, this is called “negative frequency dependence” (NFD), which is science-speak for the idea that when a trait is rare within a population it tends to have an advantage. Sign up for our Longreads newsletter for the best features, ideas, and investigations from WIRED. Instead, thick, mature facial hair is present almost exclusively on the male half of the species, and its only job is to sit there on the face of its wearer as a signal to everyone who crosses his path. If facial hair were meant to perform important functions, it would be present across both sexes. Natural selection is ruthless, and it has sent A LOT of species the way of the dodo-for instance, the dodo-but rarely, if ever, does it select for a trait in a species like that and leave half the population hanging, especially the half that makes all the babies (i.e., the most important half). It all makes sense when you look at it that way.Įxcept there’s a problem with this theory: It leaves out 50 percent of the population, i.e., females. Beards and mustaches are also on the face, which is connected to the head, which loses a lot of heat out of its top if it isn’t covered by hair. Beards and mustaches are around the mouth, after all, and the mouth takes in food and other particles that might carry disease. In the early days of studying this kind of stuff, evolutionary biologists thought it might serve thermoregulatory or prophylactic purposes similar to body hair and pubic hair. Pubic hair also helps reduce friction, as well as provides a layer of protection from bacteria and other pathogens.īut facial hair? You will notice it doesn’t appear on that handy list of adaptive hairy traits.Armpit hair, technically called “axillary” hair, collects and disseminates pheromones while acting like the WD-40 of body hair, reducing friction between skin on the underside of the arm and skin on the side of the chest as we walk and swing our arms.Eyebrows impede sweat from getting in your eyes. ![]() ![]()
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