PerspectivesAre you interested in submitting a Perspective Article? Be sure to read The Science Advisory Board's Editorial Guides for Perspective Articles. Click here. When, How and Why Did Humankind Lose Its Fur? by Sergey N.Rumyantsev, M.D., Ph.D., DSc Approximately 5,000 mammal species exist on earth. Nearly all of them have fur covering almost the entire body. Naked representatives are seldom found among mammal species. Evidently, the nakedness is disadvantageous for most mammals, and natural selection cruelly sweeps out relevant mutations. In contrast to a plethora of mammals, including his closest living relatives the chimpanzee, gorilla, and orangutan, Homo sapiens is naked. Humans are the only furless primates. Many anthropologists have asked why humankind has lost its pretty fur. It is absolutely impossible to imagine what benefits have been provided to naked people by natural selection. Charles Darwin was convinced that no naturally selected advantage could be cited as evidence for the lack of body fur in humans [1]. However some of his followers continued to seek answers. Three main explanations for this extravagant feature have been suggested by some scientists: the body-heating theory, the body-cooling theory and the ectoparasite theory. All the explanations are based on the obvious idea that this significant loss should provide human predecessors with a very effective life-saving advantage at some specific stage of human descent. Each theory exposes its own opinion about this advantage. The body-cooling theory is that the human lost his fur in order to decrease his body temperature as an adaptation to life on the hot savannah [7]. Unfortunately for this theory, the savannah stage of human evolution arose because of the global cooling of our planet toward the end of Pliocene (5.3 million years ago). According to the body-heating theory, the loss of fur may have been advantageous for hypothetical aquatic apelike ancestors to modern humans. Presumably, the ancestors had a semi-aquatic lifestyle based on foraging for food in shallow waters [3]. Fur is not an effective thermal insulator in water. At this cool environment the replacement of fur with a pertinent level of subcutaneous fat may provide the aquanauts with adequate regulation of body temperature as other aquatic mammals have. The weakest point of this theory is that no evidence for an aquatic phase of human evolution has been found. Finally, it has been suggested that some ancestors to modern humans became naked as a means to reduce the prevalence of external parasites that routinely inhabit mammalian fur [4]. A furry coat provides a very appropriate haven for parasitic insects such as ticks, lice, biting flies and other bloodsucking creatures. These ectoparasites not only bring irritation and annoyance but can inject into victims some viral, bacterial and protozoan-based diseases such as malaria, duple fever, sleeping sickness, viruses of tickborne encephalitis, West Nile and Lyme disease, all of which can cause death. Humans, by virtue of being able to build fires, construct shelters and produce clothes, would have been able to lose their fur and thereby reduce the numbers of parasites they were carrying without suffering from the cold at night or in colder climates. Besides, smooth, clear skin may have become a signal of health, like a peacock's tail. According to this newest theory, the lice infections, which are limited to the head, armpits and pubis, seem to support the parasite hypothesis. Naked mole rats also seem to support the theory: Their large colonies live underground in cramped conditions. But the combined warmth of their bodies and the confined underground space probably negate the problem of losing heat to cold air for these animals, allowing them also to become naked. Despite exposure to head lice, humans probably retained head hair for protection from the sun and to provide warmth when the air is cold. Pubic hair may have been retained for its role in enhancing pheromones or the airborne odors of sexual attraction [4] and probably in the defense of reproductive organs from attacking beasts. Analogously, the function of the throat’s defense might be performed by the men's beard. All three theories, but the ectoparasite theory especially, have presented their answers to the question why humans lost their body hair. However they do not explain when and how this transformation might have been performed. The nakedness of humans is not total but of a special mosaic kind. Fur does not cover the whole body of anatomically modern humans but only some parts of it. The fur is set locally on the head, armpits and pubis in all people, as well as on the face in men only. In contrast to the diversity in skin pigmentation, the uniqueness of these as the only hairy areas of human bodies is characteristic of all human races. This feature can help us to suppose when the nakedness of humankind arose. According to evidence from fossils, ancient artifacts, genetic analyses [2] and the relicts of molecular selection in the constitution of modern humans [5, 6], the descent of humankind occurred during the Savannah stage of anthropogenesis (between 5.3 million years ago and 200,000 years ago in Africa). After the last Ice Age began (80,000 years ago), nearly 70,000 years ago a part of the anatomically modern human population began to leave Africa, dispersing around the world and forming modern races. Evidently, the human nakedness arose between 200,000 and 70,000 years ago, i.e. before the exodus of human ancestors out of Africa. Probably, the loss of fur was a result of some solitary mutation that became selectively advantageous for humans in this new environment. Unfortunately, nothing is known about what environmental selective agent allowed the feature to spread around the ancient human population. Probably it must be found among the mightiest selective factors that govern the evolution of humankind [5]. The unique mosaic pattern of human nakedness opens the door to understanding the origin of this phenomenon. Recent achievements in the discovery of inter-individual diversity can be useful for the clarifying of this mosaicism too [6]. At the first step on this way, it should be accentuated, for instance, that in the world of mammals the nakedness is observed to be extraordinarily seldom. Nevertheless it exists. The entire species of naked mole rats is absolutely hairless. Albeit single but not-so-seldom examples of naked domesticated cats and dogs are known too. The same phenomenon has been very rarely observed in some other mammalian species. Absolutely nude (hairless) humans, both men and women, can rarely be observed between different populations and races. Additionally, some people may have partial baldness only. Other ones have local alopecia. All the variants are inborn, i.e. genetically predetermined by mutations that probably arose at the edge of primate evolution and even far earlier. The mutation can be preserved in the genome from human ancestors thanks to heterozygosity. From this point of view, the cases of total nudeness can be considered as a result of homozygosity for this mutant gene. The spread of such homozygotes among the populations of human ancestors has been precluded by natural selection. Nevertheless the mutant gene could be saved for a long time in heterozygous forms that create partial nudeness of different grades. The very seldom-seen cases of partial nudeness, for instance those observed in orangutans, seem to support this suggestion. According to the ectoparasite hypothesis [4], during the very late stages of human evolution, in the period of cultural adaptation when the nudeness became advantageous, the natural selection might have favored some heterozygotes --namely those with the special advantageous locations of hair on the head, armpits and pubis. The nature of this advantageousness is unknown. However one can suppose that the location of human fur on the face (beard) and the back of head (mane) could be associated with defense of neck from predators’ attacks. The long hair of women could be advantageous for fertilization. [1] Darwin C. (1888) The descent of man and selection in relation to sex. John Murray, London. [2] Henke W, Hardt T, Tattersall I, edrs. (2006) Handbook of Paleoanthropology, II, Primate Evolution and Human Origins. Springer. [3] Morgan E. (1997) The aquatic ape hypothesis. Souvenir Press, London. [4] Pagel M and Bodmer W. (2003) A naked ape would have fewer parasites. In: Evolutionary Theory and Processes: Modern Horizons (papers in honour of Eviatar Nevo) (Wasser SP, Ed.), p. S117-S119. Kluwer Academic Publishers, London. [5] Rumyantsev SN. (2007) Deadly Microbes Turned Some Apes into Humans . [6] Rumyantsev SN and Gerasimov VK. (2007) The Origin and Functions of Biodiversity in Infectious and Non-Infectious Diseases . In: Focus on Biodiversity Research (Schwartz J, Ed.), pp. 199-300. Nova Science Publishers . [7] Wheeler P. (1984) The evolution of bipedality and loss of functional body hair in humans. J. Hum. Evol 13, 91-98. ### << Previous Next >> [ View All Perspectives ] |
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