Wikipedia and the scientific community
Furlessness / hairlessness / naked bodies
One of the most obvious differences between humans, other apes and the majority of mammals, is that we are not covered in a thick coat of fur. When Desmond Morris used the term: "the naked ape" it was clear to which species he was referring, even though we are not completely furless.
The only other species of naturally occurring furless or reduced fur mammals, are:
All, except for the last three, are or have been at some recent point in their evolutionary past, aquatic or semi-aquatic species. The first two groups consist of fully aquatic mammals that most probably started to lose their fur some time after entering the sea some 30-60 million years ago. Seals and other pinnipeds, which are semi-aquatic, have a thick coat of fur as babies which in a few very large species is lost in adulthood. Hippopotami (from the Greek meaning Horse of the River) spend most of their time during the day in water and have no fur at all; while the ancestors of pigs, elephants and rhinos probably spent a significant part of their past evolving in or near rivers, lakes or swamps and lost most of their fur. The most conspicuous exception is the naked mole-rat, which lives entirely underground, another environment where fur is more of a hindrance than a benefit.
There is one obvious reason why aquatic mammals have lost their fur: it's not very efficient in water at preserving body temperature and it probably creates weight and drag. Naked skin provides less resistance in water, enabling the body to move faster while expending less energy and making it possible for an individual to stay submerged longer. A far more effective insulator for larger mammals against heat loss in the water is fat, especially when it forms a thick layer under the skin as it does in aquatic and semi-aquatic mammals and in humans. (Smaller animals such as voles and otters cannot carry a fat layer, and instead have adapted their fur coat to make it water repellent).
In "The Naked Darwinist" (2008) Elaine Morgan asks why science has failed to come up with any credible explanation of why human beings are relatively furless. The main reason, she surmises, is that they haven't, so they ignore it. She says:
TRADITIONAL EXPLANATIONS FOR HUMAN FURLESSNESS
1. Sexual selection: Darwin supposed that our nakedness might be due to sexual selection, but this usually involves the exaggeration of features in one sex and not the other, but human nakedness affects both males and females in humans, although arguably women have less overall body hair than men.
2. Ectoparasites: It has been suggested that losing our fur helped our ancestors to get rid of burdensome parasites that threatened their survival, eg: fleas, lice, etc. But the majority of furry animals continue to be plagued by these parasites and manage to survive. And the fleas and body lice that dwell on humans continue to do so today.
3. We are not furless: Some scientists believe that we are not in fact furless at all, seeing as we have a great many hair follicles, and in some cases they are closer together than even on a chimpanzee. However, this still does not explain the fact that many of our hair follicles are so short that they do not appear above the surface of the skin.
4. To prevent overheating: This went hand in hand with the now generally discredited savannah theory, which proposed that we lost our fur in order to cool down when hunting our prey over the hot savannah. But if so, why has no other predatory animal on the savannah lost its fur, or indeed, why hasn't its prey? In fact, fur is a valuable insulator on the savannah, protecting the animal from overheating during the day as well as keeping them warm in the usually very cold temperatures at night. If you shave a patch of fur off a furry mammal, such as a sheep, its body temperature will rise when exposed to high temperatures.
5. Large mammal adaption: Some think that elephants and rhinoceroses may have lost their fur because the ratio of surface area to body mass is such that core body temperature can be preserved without the need of a fur coat, and our ancestors, being large mammals, didn't need it either. However, the size theory doesn't work because gorillas, which are larger than humans, would have lost their fur too.
6. We don't know: this is the general scientific consensus today, or it would be, if scientists actually admitted it. The truth is that in general they ignore the question of why we have no fur and most books on the subject don't even mention it. The question rarely appears in exam papers and it is not generally taught on anthropology courses.
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