Why Humans and Their Fur Parted Ways

Illustration by Michael Rothman
Before
An Australopithecus, sporting full-bodied
fur about four million years ago.

After
An archaic human walked fur-free about
1.2 million years ago, carrying fire on the savanna

ONE of the most distinctive evolutionary changes as humans parted company from their fellow apes was their loss of body hair. But why and when human body hair disappeared, together with the matter of when people first started to wear clothes, are questions that have long lain beyond the reach of archaeology and paleontology.

Ingenious solutions to both issues have now been proposed, independently, by two research groups analyzing changes in DNA. The result, if the dates are accurate, is something of an embarrassment. It implies we were naked for more than a million years before we started wearing clothes.

Dr. Alan R. Rogers, an evolutionary geneticist at the University of Utah, has figured out when humans lost their hair by an indirect method depending on the gene that determines skin color. Dr. Mark Stone- king of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, believes he has established when humans first wore clothes. His method too is indirect: it involves dating the evolution of the human body louse, which infests only clothes.

Meanwhile a third group of researchers, resurrecting a suggestion of Darwin, has come up with a novel explanation of why humans lost their body hair in the first place.

Mammals need body hair to keep warm, and lose it only for special evolutionary reasons. Whales and walruses shed their hair to improve speed in their new medium, the sea. Elephants and rhinoceroses have specially thick skins and are too bulky to lose much heat on cold nights. But why did humans, the only hairless primates, lose their body hair?

One theory holds that the hominid line went through a semi-aquatic phase — witness the slight webbing on our hands. A better suggestion is that loss of body hair helped our distant ancestors keep cool when they first ventured beyond the forest's shade and across the hot African savannah. But loss of hair is not an unmixed blessing in regulating body temperature because the naked skin absorbs more energy in the heat of the day and loses more in the cold of the night.

Dr. Mark Pagel of the University of Reading in England and Dr. Walter Bodmer of the John Radcliffe Hospital in Oxford have proposed a different solution to the mystery and their idea, if true, goes far toward explaining contemporary attitudes about hirsuteness. Humans lost their body hair, they say, to free themselves of external parasites that infest fur — blood-sucking lice, fleas and ticks and the diseases they spread.

Paul Smith for The New York Times
Included on the list of hairless mammals is the hippopotamus.
It is believed that mammals lose their hair only for particular
evolutionary reasons.

Once hairlessness had evolved through natural selection, Dr. Pagel and Dr. Bodmer suggest, it then became subject to sexual selection, the development of features in one sex that appeal to the other. Among the newly furless humans, bare skin would have served, like the peacock's tail, as a signal of fitness. The pains women take to keep their bodies free of hair — joined now by some men — may be no mere fashion statement but the latest echo of an ancient instinct. Dr. Pagel's and Dr. Bodmer's article appeared in a recent issue of The Proceedings of the Royal Society.

Dr. Pagel said he had noticed recently that advertisements for women's clothing often included a model showing a large expanse of bare back. "We have thought of showing off skin as a secondary sexual characteristic but maybe it's simpler than that — just a billboard for healthy skin," he said.

The message — "No fleas, lice or ticks on me!" — is presumably concealed from the conscious mind of both sender and receiver.

There are several puzzles for the new theory to explain. One is why, if loss of body hair deprived parasites of a refuge, evolution allowed pubic hair to be retained. Dr. Pagel and Dr. Bodmer suggest that these humid regions, dense with sweat glands, serve as launching pads for pheromones, airborne hormones known to convey sexual signals in other mammals though not yet identified in humans.

Another conundrum is why women have less body hair than men. Though both sexes may prefer less hair in the other, the pressure of sexual selection in this case may be greater on women, whether because men have had greater powers of choice or an more intense interest in physical attributes. "Common use of depilatory agents testifies to the continuing attractions of hairlessness, especially in human females," the two researchers write.

Dr. David L. Reed, a louse expert at the University of Utah, said the idea that humans might have lost their body hair as a defense against parasites was a "fascinating concept." Body lice spread three diseases — typhus, relapsing fever and trench fever — and have killed millions of people in time of war, he said.

But others could take more convincing. "There are all kinds of notions as to the advantage of hair loss, but they are all just-so stories," said Dr. Ian Tattersall, a paleoanthropologist at the American Museum of Natural History in New York.

Causes aside, when did humans first lose their body hair? Dr. Rogers, of the University of Utah, saw a way to get a fix on the date after reading an article about a gene that helps determine skin color. The gene, called MC1R, specifies a protein that serves as a switch between the two kinds of pigment made by human cells. Eumelanin, which protects against the ultraviolet rays of the sun, is brown-black; pheomelanin, which is not protective, is a red-yellow color.

Three years ago Dr. Rosalind Harding of Oxford University and others made a worldwide study of the MC1R gene by extracting it from blood samples and analyzing the sequence of DNA units in the gene. They found that the protein made by the gene is invariant in African populations, but outside of Africa the gene, and its protein, tended to vary a lot.

Dr. Harding concluded that the gene was kept under tight constraint in Africa, presumably because any change in its protein increased vulnerability to the sun's ultraviolet light, and was fatal to its owner. But outside Africa, in northern Asia and Europe, the gene was free to accept mutations, the constant natural changes in DNA, and produced skin colors that were not dark.

Reading Dr. Harding's article recently as part of a different project, Dr. Rogers wondered why all Africans had acquired the same version of the gene. Chimpanzees, Dr. Harding had noted, have many different forms of the gene, as presumably did the common ancestor of chimps and people.

As soon as the ancestral human population in Africa started losing its fur, Dr. Rogers surmised, people would have needed dark skin as a protection against sunlight. Anyone who had a version of the MC1R gene that produced darker skin would have had a survival advantage, and in a few generations this version of the gene would have made a clean sweep through the population.

There may have been several clean sweeps, each one producing a more effective version of the MC1R gene. Dr. Rogers saw a way to put a date on at least the most recent sweep. Some of the DNA units in a gene can be changed without changing the amino acid units in the protein the gene specifies. The MC1R genes Dr. Harding had analyzed in African populations had several of these silent mutations. Since the silent mutations accumulate in a random but steady fashion, they serve as a molecular clock, one that started ticking at the time of the last sweep of the MC1R gene through the ancestral human population.

From the number of silent mutations in African versions of the MC1R gene, Dr. Rogers and two colleagues, Dr. David Iltis and Dr. Stephen Wooding, calculate that the last sweep probably occurred 1.2 million years ago, when the human population consisted of a mere 14,000 breeding individuals. In other words, humans have been hairless at least since this time, and maybe for much longer. Their article is to appear in a future issue of Current Anthropology.

The estimated minimum date for human hairlessness seems to fall in reasonably well with the schedule of other major adaptations that turned an ordinary ape into the weirdest of all primates. Hominids first started occupying areas with few shade trees some 1.7 million years ago. This is also the time when long limbs and an external nose appeared. Both are assumed to be adaptations to help dissipate heat, said Dr. Richard Klein, an archaeologist at Stanford University. Loss of hair and dark skin could well have emerged at the same time, so Dr. Rogers' argument was "completely plausible," he said.

From 1.6 million years ago the world was in the grip of the Pleistocene ice age, which ended only 10,000 years ago. Even in Africa, nights could have been cold for fur-less primates. But Dr. Ropers noted that people lived without clothes until recently in chilly places like Tasmania and Tierra del Fuego.

Chimpanzees have pale skin and are born with pale faces that tan as they grow older. So the prototype hominid too probably had fair skin under dark hair, said Dr. Nina Jablonski, an expert on the evolution of skin color at the California Academy of Sciences. "It was only later that we lost our hair and at the same time evolved an evenly dark pigmentation," she said.

Remarkable as it may seem that genetic analysis can reach back and date an event deep in human history, there is a second approach to determining when people lost their body hair, or at least started to wear clothes. It has to do with lice. Humans have the distinction of being host to three different kinds: the head louse, the body louse and the pubic louse. The body louse, unlike all other kinds that infect mammals, clings to clothing, not hair. It presumably evolved from the head louse after humans lost their body hair and started wearing clothes.

Dr. Stoneking, together with Dr. Ralf Kittler and Dr. Manfred Kayser, report in today's issue of Current Biology that they compared the DNA of human head and body lice from around the world, as well as chimpanzee lice as a point of evolutionary comparison. From study of the DNA differences, they find that the human body louse indeed evolved from the louse, as expected, but that this event took place surprisingly recently, sometime between 42,000 and 72,000 years ago. Humans must have been wearing clothes at least since this time.

Modern humans left Africa about 50,000 years ago. Dr. Stoneking and his colleagues say the invention of clothing may have been a factor in the successful spread of humans around the world, especially in the cooler climates of the north.

Dr. Stoneking said in an interview that clothing could also have been part of the suite of sophisticated behaviors, such as advanced tools, trade and art, that appear in the archaeological record some 50,000 years ago, just before humans migrated from Africa.

The head louse would probably have colonized clothing quite soon after the niche became available — within thousands and tens of thousands of years, Dr. Stoneking said. So body lice were probably not in existence when humans and Neanderthals diverged some 250,000 or more years ago. This implies that the common ancestor of humans and Neanderthals did not wear clothes and therefore probably Neanderthals didn't either.

But Dr. Klein, the Stanford archeologist, said he thought Neanderthals and other archaic humans must have produced clothing of some kind in order to live in temperate latitudes like Europe and the Far East. Perhaps the body lice don't show that, he suggested, because early clothes were too loose fitting or made of the wrong material.

Dr. Stoneking said he got the idea for his louse project after one of his children came home with a note about a louse infestation in school. The note assured parents that lice could only live a few hours when away from the human body, implying to Dr. Stoneking that their evolution must closely mirror the spread of humans around the world.

The compilers of Genesis write that as soon as Adam and Eve realized they were naked, they sewed themselves aprons made of leaves from the fig tree, and that the Creator himself made them more durable skin coats before evicting them. But if Dr. Rogers and Dr. Stoneking are correct, humans were naked for a million years before they noticed their state of undress and called for the tailor.

Copyright the NY Times. For educational purposes only and not for commercial use.

From beyondveg.com:

When was fire first
controlled by human beings?

So the next question is obvious: How long have fire and cooking been around, then, and how do we know whether that length of time has been long enough for us to have adapted sufficiently?

Let's take the question one part at a time. The short answer to the first part of the question is that fire was first controlled by humans anywhere from about 230,000 years ago to 1.4 or 1.5 million years ago, depending on which evidence you accept as definitive.

Evidence for very early control of fire is sparse and ambiguous. The earliest evidence for control of fire by humans, in the form of fires at Swartkrans, South Africa and at Chesowanja, in Kenya, suggests that it may possibly have been in use there as early as about 1.4 or 1.5 million years ago.[100] However, the interpretation of the physical evidence at these early sites has been under question in the archaeological community for some years now, with critics saying these fires could have been wildfires instead of human-made fires. They suggest the evidence for human control of fire might be a misreading of other factors, such as magnesium-staining of soils, which can mimic the results of fire if not specifically accounted for. For indisputable evidence of fire intentionally set and controlled by humans, the presence of a hearth or circle of scorched stones is often demanded as conclusive proof,[101] and at these early sites, the evidence tying the fires to human control is based on other factors.

Earliest dates for control of fire accepted by skeptical critics. At the other end of the timescale, these same critics who are only willing to consider the most unequivocal evidence will still admit that at least by 230,000 years ago[102] there is enough good evidence at at least one site to establish fire was under control at this time by humans. At this site, called Terra Amata, an ancient beach location on the French Riviera, stone hearths are found at the center of what may have been huts; and more recent sources may put the site's age at possibly 300,000 years old rather than 230,000.[103]
Somewhat further back--from around 300,000 to 500,000 years ago--more evidence has been accumulating recently at sites in Spain and France[104] that looks as if it may force the ultraconservative paleontologists to concede their 230,000-year-ago date is too stingy, but we'll see.

And then there is Zhoukoudian cave in China, one of the most famous sites connected with Homo erectus, where claims that fire may have been used as early as 500,000 to 1.5 million years ago have now largely been discredited due to the complex and overlapping nature of the evidence left by not just humans, but hyenas and owls who also inhabited the cave. (Owl droppings could conceivably have caught fire and caused many of the fires.) Even after discounting the most extreme claims, however, it does seem likely that at least by 230,000 to 460,000 years ago humans were using fire in the cave[105], and given scorching patterns around the teeth and skulls of some animal remains, it does appear the hominids may have done this to cook the brains (not an uncommon practice among hunting-gathering peoples today).[106]

The most recent excavation with evidence for early use of fire has been within just the last couple of years in France at the Menez-Dregan site, where a hearth and evidence of fire has been preliminarily dated to approximately 380,000 to 465,000 years. If early interpretations of the evidence withstand criticism and further analysis, the fact that a hearth composed of stone blocks inside a small cave was found with burnt rhinoceros bones close by has provoked speculation that the rhino may have been cooked at the site.[107]

Crux of the question: first control of fire vs. earliest widespread use. Now of course, the crucial question for us isn't just when the earliest control of fire was; it's at what date fire was being used consistently--and more specifically for cooking, so that more-constant genetic selection pressures would have been brought to bear. Given the evidence available at this time, most of it would probably indicate that 125,000 years ago is the earliest reasonable estimate for widespread control.*[108] Another good reason it may be safer to base adaptation to fire and cooking on the figure of 125,000 years ago is that more and more evidence is indicating modern humans today are descended from a group of ancestors who were living in Africa 100,000-200,000 years ago, who then spread out across the globe to replace other human groups.[109] If true, this would probably mean the fire sites in Europe and China are those of separate human groups who did not leave descendants that survived to the present. Given that the African fire sites in Kenya and South Africa from about 1.5 million years ago are under dispute, then, widespread usage at 125,000 years ago seems the safest figure for our use here.
Sequence of stages in control: fire for warmth vs. fire for cooking. One thing we can say about the widespread use of fire probable by 125,000 years ago, however, is that it would almost certainly have included the use of fire for cooking.* Why can this be assumed? It has to do with the sequence for the progressive stages of control over fire that would have had to have taken place prior to fire usage becoming commonplace. And the most interesting of these is that fire for cooking would almost inevitably have been one of the first uses it was put to by humans, rather than some later-stage use.*

The first fires on earth occurred approximately 350 million years ago--the geological evidence for fire in remains of forest vegetation being as old as the forests themselves.[110] It is usual to focus only on fire's immediately destructive effects to plants and wildlife, but there are also benefits. In response to occasional periodic wildfires, for example, certain plants and trees have evolved known as "pyrophytes," for whose existence periodic wildfires are essential. Fire revitalizes them by destroying their parasites and competitors, and such plants include grasses eaten by herbivores as well as trees that provide shelter and food for animals.[111]

Opportunistic exploitation of animal kills by predators after wildfires. Fires also provide other unintended benefits to animals as well. Even at the time a wildfire is still burning, birds of prey (such as falcons and kites)--the first types of predators to appear at fires--are attracted to the flames to hunt fleeing animals and insects. Later, land-animal predators appear when the ashes are smoldering and dying out to pick out the burnt victims for consumption. Others, such as deer and bovine animals appear after that to lick the ashes for their salt content. Notable as well is that most mammals appear to enjoy the heat radiated at night at sites of recently burned-out fires.[112]

It would have been inconceivable, therefore, that human beings, being similarly observant and opportunistic creatures, would not also have partaken of the dietary windfall provided by wildfires they came across. And thus, even before humans had learned to control fire purposefully--and without here getting into the later stages of control over fire--their early passive exposures to it would have already introduced them, like the other animals, to the role fire could play in obtaining edible food and providing warmth.

Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.