U.K. duo suggest early humans retained fine hair to ward off parasites

U.K. duo suggest early humans retained fine hair to ward off parasites
(a) Detection of ectoparasites on unshaved (black bars) and shaved (white bars) arms. (b). Residual detection rate (derived from detection versus search time on unshaved arms) was positively correlated with hair index. Image: © The Royal Society 2011 doi: 10.1098/rsbl.2011.0987

(PhysOrg.com) -- Evolutionary biologists have long been puzzled by the question of why human beings have retained body hair. Most agree that changes to the fur that our ancestors sported came about as a means to keep cool in the hot African climate. So why then, didn’t we just lose our body hair completely, instead of having it change from long thick fur, to short and thin hair that makes us look like we’re mostly bald all over anyway, when actually, we still have just as many hairs as we ever did? Isabelle Dean and Michael Siva-Jothy think they’ve figured it out and have published a paper in Biology Letters explaining how they believe it’s all about warding off skin parasites.

Suspecting that having fine short hair, rather than no hair at all would help us detect the presence of skin parasites such as , the two set up an experiment using volunteers from the University of Sheffield where they both work, to find out. The volunteers were made up of ten women and nineteen men each of whom had one small square on one arm shaved for testing. Hungry bed bugs were then dropped onto the bare skin to see how long it took the volunteer to feel its presence. Also timed was how long it took the bed bug to pick a spot for parking and eating. The bugs were removed just before they bit. The same experiment was performed on each volunteer on the other unshaved arm as well to provide a way to compare results.

After tallying up the results afterwards, the researchers found that more hair causes bed bugs to take a lot longer to find a spot to eat, which makes sense because all those little body hairs make the trip more difficult. Sort of like the difference between us humans walking down the street or wading through a dense thicket. What’s perhaps more surprising, but maybe shouldn’t be, is that the volunteers all took much longer to feel the bug crawling on their skin on the shaved patch, then on the unshaved arm, indicating that the presence of fine hair helps us to feel such parasites on our skin and to get rid of them before they can begin biting us.

Not surprisingly, men were better at detecting bed bugs on the unshaved arm, due to having thicker and longer hair than women. As to why men are generally hairier looking than women, the researchers suggest it might be due to something as simple as women preferring men with fewer parasites on them, which would imply more .


Explore further

New model suggests early humans lost fur after developing bipedalism

More information: Human fine body hair enhances ectoparasite detection, Biol. Lett. Published online before print December 14, 2011, doi: 10.1098/rsbl.2011.0987

Abstract
Although we are relatively naked in comparison with other primates, the human body is covered in a layer of fine hair (vellus and terminal hair) at a relatively high follicular density. There are relatively few explanations for the evolutionary maintenance of this type of human hair. Here, we experimentally test the hypothesis that human fine body hair plays a defensive function against ectoparasites (bed bugs). Our results show that fine body hair enhances the detection of ectoparasites through the combined effects of (i) increasing the parasite's search time and (ii) enhancing its detection.

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Citation: U.K. duo suggest early humans retained fine hair to ward off parasites (2011, December 15) retrieved 20 August 2019 from https://phys.org/news/2011-12-uk-duo-early-humans-retained.html
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Dec 15, 2011
Mammalian hair performs a similar tactile function to that of feathers. Small forces applied to the appendage are transmitted by leverage to nerve endings in the follicle, allowing the bearer to sense much more subtle stimuli than direct contact. Birds feel air currents this way and locate thermal updrafts. Mammals feel parasites, burrs, and slight air currents similarly.

Dec 15, 2011
My reaction was the same as tadchem. Fine hairs enable us to feel slight air currents and other phenomena. We would have them even if parasites were not a problem.

One reason for this is that detecting parasites is not the problem but removing them. This is best done by a friend--after all they can see them and get them in places we cannot ourselves reach. It is why we groom each other.

Dec 15, 2011
I'm not sure how skin parasites would affect an individual's probability to have offspring, though.

Dec 15, 2011
So why then, didnt we just lose our body hair completely, instead of having it change from long thick fur, to short and thin hair that makes us look like were mostly bald all over anyway

Alternative explanation: Because, even in Africa, it gets cold at night?
When we remain relatively still (e.g. when sleeping) such fine hair is exceptionally good at reducing the movement of air over exposed skin - thus reducing the main heat loss mechanism under those conditions: convection

The effect is increased in very cold circumstances: The hair follicles react by raising the hair on your body - thus increasing this insulating layer of air around us.

So retaining these hairs makes us able to survive (unaided) over a larger temperature range and reduces our energy needs.

Dec 15, 2011
What about the obvious reason being the same as why males have nipples (which I am pretty sure has nothing to do with bed-bugs). I think these people should find more meaningfull work to do.

Dec 15, 2011
So if warmth is the issue why the further north one travels the less body hair people have?

Dec 15, 2011
So if warmth is the issue why the further north one travels the less body hair people have?

Have you double checked that? The further north you go bodyhair increases.

Dec 15, 2011
But aren't there more parasites in southern regions?
And doesn't more body hair - while maybe slowing down parasites on the way in - also mean that parasites are retained more easily? seems like not so much of an advantage in that case.

Dec 15, 2011
I'm not sure how skin parasites would affect an individual's probability to have offspring, though.


Parasites definitely have a fitness cost. Plus, they carry disease. You can't have offspring if you die of the plague...

Dec 15, 2011
I personally would like an explantation for male pattern baldness.

Dec 15, 2011
When we remain relatively still (e.g. when sleeping) such fine hair is exceptionally good at reducing the movement of air over exposed skin - thus reducing the main heat loss mechanism under those conditions: convection
Is it? Is this assumption or fact?

The article reminds me of the feeling of a tick making it's way up your leg. Another reason for the same number of follicles may be that this is a reversable adaptation? The farther north a species resides, the more it adapts to the seasons and the cold.

Neanderthal may have died out because it's reproduction had become seasonal like any temperate or arctic animal, and it couldn't replace battle losses as fast as the tropical cromags. Perhaps the esquimaux could eventually hibernate?

So maybe hair follicles can grow fur again if ever the need arises. Like wholly mammoths. Do elephants have hair? I don't know.

Dec 15, 2011
But aren't there more parasites in southern regions?
And doesn't more body hair - while maybe slowing down parasites on the way in - also mean that parasites are retained more easily? seems like not so much of an advantage in that case.
Humans have not had time to change much since we left Africa. Euros are still a tropical species who got there just yesterday via India.

Dec 16, 2011
Humans have not had time to change much since we left Africa.

Beards are certainly far more prevalent in Europe than in Africa or in India. Have you ever seen what happens if a black person or one from India tries to grow a beard? I'd suggest that this is already an adaptation to colder climates.

Is it? Is this assumption or fact?

E.g. from here:
http://en.wikiped...r#Warmth

Dec 16, 2011
Humans have not had time to change much since we left Africa.

Beards are certainly far more prevalent in Europe than in Africa or in India. Have you ever seen what happens if a black person or one from India tries to grow a beard? I'd suggest that this is already an adaptation to colder climates.

Is it? Is this assumption or fact?

E.g. from here:
http://en.wikiped...r#Warmth
-As is skin color itself. Genghis khan didn't conquer southeast asia because he couldn't stand the heat. But we still exhibit little divergence as a species because of our rapid spread and our penchant for conquest and recombination due to our tropical reproductive rate and resulting pressure from overpopulation.

Dec 16, 2011
By the way I can think of many black people with full beards. Islam is full of them.

Dec 17, 2011
Caucasoids are the most hairy race, I think we just have more from the neanderthal, we just cant explain why africans dont have so much, and mongoloids dont have that much, our climate range is in between, and we have the most, it doesnt make any sense, if body hair was that good for parasites, well africa have much more than europe, will anyone argue about that?
If it prevents the cold, well asia is much colder.


Dec 17, 2011
Caucasoids are the most hairy race, I think we just have more from the neanderthal, we just cant explain why africans dont have so much, and mongoloids dont have that much, our climate range is in between, and we have the most, it doesnt make any sense, if body hair was that good for parasites, well africa have much more than europe, will anyone argue about that?
If it prevents the cold, well asia is much colder.

You have a source for your musings? Are you sure that the relative number of follicles arent roughly equal and that it is the color and coarseness of the hair which makes it seem as though there is a difference?

The hairiest people Ive seen at the multicultural gym that I go to, are arabs. But I am thinking it only appears that way.

Dec 17, 2011
Arabs are caucasoids, and yes somewhere there are the hairiest( south caucasoids at general), after that is Europe, well I dont know about papuans and Australoids though, I am not talking only about the number of the follicles , maybe it is equal, but still it is strange why some have so abundant body hair and other doesnt, to me this body hair is something old that we didnt get rid of, or it comes from the neanderthal, my point is that it serves no purpose.
Still the article talks about these body hairs that even women have, so all this is a little bit off topic.

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