Why have humans got less hairy as they've evolved what biological advantage does it provide?

Question

Why have humans got less hairy as they've evolved what biological advantage does it provide?

Answer 1

They got tired of the lice and ticks...Advantage? less shampoo

Answer 2

Why Humans and Their Fur Parted Ways

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.

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 s*x 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.

Answer 3

You should try and read Elaine Morgans aquatic ape theory.

Very interesting and seems to make a lot of sense.

You have had some fantastic replies by the way!!

Answer 4

I think it was mainly to keep the body warm as we had no clothes when we were evolving.

Answer 5

I dont think we need it any more, we now have clothes to keep us warm. so our bodies use the energy for things we do need

Answer 6

Yes, the loss of need for fur is probably part of it, and the other part may involve the lack of sunlight as we migrated northward.  It was an evolutionary advantage to not have sunlight blocked from the ability to produce Vitamin D in our bodies.

Answer 7

Its not an advantage. The body answer to its environment, and try to reduce or eliminate organic waste. So since our hairs have mostly lost their original purpose, the body got evolutive pressure to get rid of it, so it could use its energy elsewhere, where it is really needed. So, it just mean, that our development strategy and anatomy is getting optimized to our current way of life.

Answer 8

if u fink abowt it we waz first 'ere wen ther ice age was an we was cold an 'airy, but now its not the ice age so we dont need so many 'airy bits an anver fing weve got jumpers n fings for  winter

Sorry Couldn't resist it

Answer 9

I believe there are currently two theories on this -- the answer being we really don't know.

One theory is that there was a time during our development when we were marine mammals, spending a lot of time in the water.

Whales, for example, have almost no hair for this reason.

The other is that, when you can wear clothes for warmth, you don't need fur.

Losing fur was an advantage because you have less parasite load when you aren't covered in fur.

Other critters, not having the option of clothes, can't afford to be furless.

Answer 10

This is a really easy question getting a lot of really bad answers.  Animals that do not need hair quickly evolve hairless forms because producing hair requires resources that the body could use elsewhere.  It's the same reason that cave fish lose their eyes and body pigment.

Answer 11

It's not so much a biological advantage to baldness, but rather an evolutionary adaptation to a warmer world.  Hair evolved as a way of keeping us warm - hence the "hairy" appearance commonly associated with Neanderthals.  The Earth is slowly warming up, so hair is unnecessary from a biological perspective.

Answer 12

Women did not like too hairy men and so they died out without passing on their genes.