hair naked ape human biology

Human hairiness

Why is the “naked ape” not really naked?

Desmond Morris called the human species ”The Naked Ape” in his famous book of the same title. But even without clothes, when we are indeed naked, we are not hairless. Our entire body (with the notable exceptions of the insides of our hands and feet, the area around the nipples, and the lips) is covered with hairs.

However, disregarding head, armpits and pubic region, our hairs are thin, short, useless for camouflage and ineffective in protecting us against injury, cold, and radiation. What led to the almost complete disappearance of our fur and why men are hairier than women are questions for which there is no single answer. Obviously, wearing clothes made a thick coat of fur redundant. The problem is, humans lost their fur more than a million years ago, long before wearing clothes. Another theory suggests that we are relatively hairless, because we retained the hairlessness of newborns into our adult life. But although some mammals do have naked and helpless newborns, such mammals usually have large litters, capable of warming each other. Humans, however, tend to give birth to a single child.

Did human evolution perhaps include a semi-aquatic stage? Since hair traps air and causes drag, truly aquatic mammals like whales and dugongs have become hairless. An aquatic life could explain the human’s upright posture, some peculiarities about the direction of our hairs on our backs, the hair growth on our heads, and the development of subcutaneous fat. But there is no fossil evidence in support of this idea and physiological objections have been raised as well. So, could chasing after game and the need to prevent overheating, in other words could temperature regulation have been the force that made us lose our fur? Although widely accepted, this theory also has its critics. Cheetahs and endurance runners like wolves have not lost their fur. Moreover, human babies and women are less hairy than men, but would hardly have participated in chasing game. Adult elephants are indeed almost hairless for thermoregulatory reasons, but they don’t run after game and their young (contrary to humans) are hairier than the adults.

So, could a lack of body hair have been an advantage in some other way? If early humans inhabited tropical grasslands and possessed a furry coat, sticky and prickly plant seeds, entangled in the fur, could have caused irritation and possibly infections. Moreover, a dense coat of hair, especially when soiled by food leftovers due to messy eating habits, would have attracted pesky insects like flies and provided shelter for a multitude of disease-carrying organisms like mites, ticks, and fleas. Thus, individuals with a less luxuriant growth of body hair would have been preferred as prospective mating partners, signalling through their hairlessness that they were healthy individuals, free of parasites. Areas first free of hairs would have been the breasts in females, not only as a sexual signal aimed at males, but also as an advantage for the suckling infant. Female lack of body hair would have been compensated by an increase in subcutaneous fat (less important for males as they retained more of their body hair than the females). A beard in males, as an outward expression of the male sex hormone testosterone, probably signified status and indicated to females that the bearded individual had reached a prominent position despite the disadvantages of hairiness and, therefore, had to be a carrier of ‘good genes’.

But what about the hair of the armpits and the pubic region? It has been suggested that these hairy patches served as scent-dispensers, arousing the opposite sex. Well, maybe 100,000 years ago – before the invention of perfume and soap.

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© Dr V.B. Meyer-Rochow and, 2016.
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