Lice Tell Us When We Started Wearing Clothes

[lpetrich]

In the most recent Nature's Science Update, there is an article about using lice to date when we started wearing clothes (http://www.nature.com/nsu/030818/030818-7.html). We have head lice, Pediculus humanus capitis, which live in the hair on our heads, and body lice, Pediculus humanus humanus, which live in clothing. And Kittler, Kayser and Stoneking report in Molecular Evolution of Pediculus humanus and the Origin of Clothing. Current Biology, 13, 1414 - 1417, (2003). (http://www.current-biology.com/content/article/abstract?uid=PIIS0960982203005074) that the two subspecies diverged about 30,000 to 114,000 years ago, that head lice are more divergent than body lice, and that lice from Africa are more divergent than lice from elsewhere. That date was found with the help of a comparison to chimp lice.

Evidence of weaving dates back to 27,000 years ago, and needles date back to 40,000 years ago, and there is archeological and genetic evidence that our present human species left Africa at about 50,000-100,000 years ago. Which is right on the dot for the split-off of body lice. Leaving Africa would have been made easier by wearing clothes; and that could have been the time that we started wearing clothes much of the time -- and creating an alternative habitat for our lice.

We have a third species of louse, the pubic or crab louse (Phthirus pubis), and Stoneking's team will be investigating those lice to get an idea of when we lost most of our body hair. Which had forced our lice into two separate "islands" on our bodies.

[MrDarwin]

Not to rain on your lousy parade :) but how can one of two diverging taxa be more "divergent" than the other?

BTW human pubic (crab) lice, which are in a different genus, are apparently more closely related to gorilla lice than to human head or body lice.

There is a pretty decent article in the New York Times:

Why Humans and Their Fur Parted Ways (http://www.nytimes.com/2003/08/19/science/19HAIR.html)

and another in the Washington Post:

Study Uses Lice DNA to Find When Clothing First Appeared (http://www.washingtonpost.com/wp-dyn/articles/A11847-2003Aug18.html)

and see also:

'Lousy' Study Shows Clothing 70,000 Years Old (http://story.news.yahoo.com/news?tmpl=story&cid=585&ncid=585&e=5&u=/nm/20030818/sc_nm/science_lice_dc)

The hypotheses of some of the researchers mentioned in these articles were discussed at some length here several months ago.

[Kosh]

lpetrich, do you have any information on what the evolutionary advantage would have been to losing a majority of our body hair?

[lpetrich]

Originally posted by MrDarwin
Not to rain on your lousy parade :) but how can one of two diverging taxa be more "divergent" than the other? ...This is divergence inside a population; apparently body lice have less in-population divergence than head lice do.

[RBH]

Kosh askedlpetrich, do you have any information on what the evolutionary advantage would have been to losing a majority of our body hair?I'm not Ipetrich, but one hypothesis is to reduce parasites. Less hair = less 'cover' for skin-surface-dwelling parasites, like lice. I have a memory of a movie (documentary?) in which chimps engaged in long episodes of mutual grooming, with the occasional cracking of a caught parasite in the groomers teeth.

RBH

[lpetrich]

Originally posted by Kosh
lpetrich, do you have any information on what the evolutionary advantage would have been to losing a majority of our body hair? That New York Times link discusses that very question. And mentions several theories:

Loss of body hair was convenient for surviving in the hot grassland areas of Africa.

Also, it's a good way of reducing one's flea and louse population.

Pubic hair was retained because of its sweat glands, which produce pheromonal smells.

As to when it was lost, there's a possible genetic clue -- the gene MC1R, which is involved in switching between brown-black eumelanin and red-yellow pheomelanin. Not surprisingly, the darker one is better at protecting against solar UV than the lighter one.

In human populations, Africans have very constrained MC1R, because of being exposed to all that solar UV, while non-Africans usually live where there is less solar UV -- and have less-constrained MC1R.

In chimps, however, MC1R is also relatively unconstrained, perhaps because of a combination of being furry and of living in forests -- both of which are sun blockers.

From African populations' neutral variants of MC1R, Drs. David Iltis and Stephen Wooding have estimated that the minimum time was about 1.2 million years ago, about the time when Homo erectus emerged.

However, hominids had started living in areas at about 1.7 million years ago, which is when long limbs and an external nose started to appear -- both good for dissipating heat.

[wiploc]

Originally posted by Kosh
lpetrich, do you have any information on what the evolutionary advantage would have been to losing a majority of our body hair?

In Our Kind, Marvin Harris suggests that it was so we could radiate heat better while hunting --- the kind of hunt where you chase an animal for days, until it drops of exhaustion.
crc

[wiploc]

Originally posted by lpetrich

Pubic hair was retained because of its sweat glands, which produce pheromonal smells.

I have trouble with this one. Doesn't it require that the people who didn't smell right died off, right, thus extending the hairy-pubes genes thru the population?

Are we supposed to think that ...

A. Even today, people refuse to mate with people whose pubic area lacks the proper pheromonal smells.

Or

B. While hairy-pubes used to be necessary to getting laid, we have evolved since then in such a way that we no longer need these pheromones to reproduce.

Or

C. Some other explanation I haven't thought of.

Seems to me that if the pheromones produced enough evolutionary pressure to preserve our hairy-pube genes, then we wouldn't have many people today shaving their pubes --- or bathing before sex.
crc

[Kosh]

Originally posted by wiploc
In Our Kind, Marvin Harris suggests that it was so we could radiate heat better while hunting --- the kind of hunt where you chase an animal for days, until it drops of exhaustion.
crc

And so those with less hair could hunt longer, thus making them more successfull in bringing home more meat, thus giving them more offspring, passing on the hairless genes....?

[Calzaer]

Even today, people refuse to mate with people whose pubic area lacks the proper pheromonal smells.

I don't know about you, but an improper-smelling pubic area makes me excessively disinclined to mate with a female, other qualities notwithstanding.

[wiploc]

Originally posted by Calzaer
I don't know about you, but an improper-smelling pubic area makes me excessively disinclined to mate with a female, other qualities notwithstanding.

Not making jokes here. Do you seriously believe that there are pheromones that you won't mate without?
crc

[schu]

Originally posted by lpetrich
Pubic hair was retained because of its sweat glands, which produce pheromonal smells.

I heard a Dr. say that pubic hair and underarm hair acted as a lubricant. Could this be possible?

[Kosh]

Originally posted by schu
I heard a Dr. say that pubic hair and underarm hair acted as a lubricant. Could this be possible?

NFW. Once you've had shaved, you never go back! Frees up both your hands too...

[RufusAtticus]

We need to remember that our ancestors didn't bathe every day. The physical advantages of having hair in pubic or underarm regions might not manifest themselves until after 5 years without a bath.

Of course, sexual selection for those traits could be cultural. For example, the existance of merkins.