When we look at a primate, one of the first characteristics we identify is the amount of hair, which is quite thick and even matted, covering the entire body of the animal. However, the human being is the only one among the existing primates, an order that includes gorillas, lemurs and monkeys in general, to have few hairs. The explanation lies in the process of human evolution.
However, a correction needs to be made. In fact, humans do have as much fur as some species of apes. To be precise, there are at least five million hair follicles scattered throughout the skin, but most of these follicles are shallow and produce very short and fine hairs, unlike other primates.
“Technically, we have hair all over our bodies, but they are miniature follicles”, explains Tina Lasisi, a bioanthropologist at the University of Southern California, in the United States, for the BBC. “They are miniaturized to the point where, functionally, they no longer protect us,” she adds.
Now, looking at the human body, it’s easy to see where the deepest and thickest follicles are: in the head. In some ways, this covering resembles the hair so common in most primates. Other similarities are identified in the face after puberty in men, the beard. In addition, there are also thicker underarm hairs and pubic hair.
Why do humans seem to have less hair than apes?
Science still doesn’t know why hairs have differentiated between humans, but there are some really interesting hypotheses. Among them, the most accepted is that the decrease in hair is related to the body’s need for cooling, known as the “savannah hypothesis”.
Here, it is worth explaining that, during the Pleistocene period, the Standing man and the other hominid species practiced persistent hunting in the savannah. This means that, to capture prey, the animal was chased for hours until it reached its limit of exhaustion. Because of the very intense activity and heat, they were in danger of overheating.
While hominids lost their hair, the sweat glands took on the function of cooling the body better, through sweat. “We can imagine, with a little confidence, that this happens 1.5 to 2 million years ago”, says Lasisi.
More hypotheses explain the few hairs in humans
Another hypothesis about the loss of hair characteristic of primates involves the issue of parasites, known as the ectoparasite hypothesis. Among the proponents of this idea is Mark Pagal, professor of evolutionary biology at the University of Reading, UK.
Before we continue, it is worth making a brief consideration. Ectoparasites are arthropods that depend on the skin of a host in at least some stage of life. Included in this classification are insects (fleas, flies and even lice) and mites (ticks).
“Parasites probably were and still are one of the biggest selective forces in our evolutionary history”, defends Pagal. points out. “And these flies are specialized in landing and living in the fur and depositing their eggs”, he completes.