Dark-skinned H. erectus had tuberculosis?

Most ancient case of tuberculosis found in 500,000-year-old human; points to modern health issues:

Although most scientists believe tuberculosis emerged only several thousand years ago, new research from The University of Texas at Austin reveals the most ancient evidence of the disease has been found in a 500,000-year-old human fossil from Turkey.
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The research team identified two shared characteristics in the communities: a path of migration from low, tropical latitudes to northern temperate regions and darker skin color.

People with dark skin produce less vitamin D because the skin pigment melanin blocks ultraviolet light. And, when they live in areas with lower ultraviolet radiation such as Europe, their immune systems can be compromised.

It is likely that Homo erectus had dark skin because it evolved in the tropics, Kappelman explained. After the species moved north, it had to adapt to more seasonal climates. The researchers hypothesize the young male's body produced less vitamin D and this deficiency weakened his immune system, opening the door to tuberculosis.

The point about dark-skinned people and weaker immune systems due to Vitamin D deficiency is well taken. I've blogged Vitamin D deficiency before. I find it interesting because I am curious about its role in the evolution of human skin color. It seems that many Eurasian populations have become much lighter skinned within the last 10,000, and I've wondered why. For example, imagine that infectious diseases became a bigger selective pressure as population densities increased due to agriculture. Additionally, with agriculture the range of nutrient deficiencies, including of Vitamin D, would also loom larger with a less varied diet. Perhaps this was a selective environment which shifted these populations toward rapid depigmentation as an adaptive response?

But, I do have to offer that the hypothesis that Eurasian Homo erectus suffered Vitamin D deficiency because of dark-skin is rather unlikely. Populations can lose their pigmentation rather quickly, over a few thousand years (see the selection coefficients around SLC24A5). These are loss of function mutations, and it is often quite easy to break things as opposed to gaining function. I read once in my youth that Neandertals might have had dark-skin because of bone morphology which resembled rickets. We now have data which suggests that Neandertals were depigmented. This makes sense, Neandertals and their precursors resided in northern Eurasia for hundreds of thousands of years. Evolution works. Unless a hominid population are very recent immigrants to a region it seems unlikely to posit that because their ancestors had dark-skin they must also have had dark skin. After all, the ancestors of Swedes only emerged from Africa in the last 50,000 years, but they no longer have dark skin (though it turns out that most of the selection for lack of pigmentation might have occurred within the last 15,000 years, at least on three loci, SLC45A2, SLC24A5 and OCA2).

Note: The Dmanisi fossils are well over 1 million years old, so I see no reason to assume that this individual was a descendant of recent immigrants are a priori grounds.

Update: John Hawks is skeptical of the skin color connection too.

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"People with dark skin produce less vitamin D because the skin pigment melanin blocks ultraviolet light."

Is the difference in UV levels so big that it explains the difference in melanin? I've always doubted it. Especially because the change happens at a relatively short distance.

Isn't it more likely that lack of UV was due to development of clothing? Even today (during an interglacial) only the summer months are warm enough to go about naked.

By Lassi Hippeläinen (not verified) on 06 Dec 2007 #permalink

There are big differences in UV radiation with latitude, especially in winter.

The Tierra del Fuegans dealt with nakedness and cold by covering themselves in grease.

But the conundrum is that Australian aboriginals have been in the southern parts of Australia for 40,000 years but didn't lose pigmentation, or not much, while modern Australians can suffer vitamin D deficiency at those latitudes even with pale skin. Maybe the answer is that the aboriginal people never became completely sedentary and turned to farming, and they remained largely naked and lived outdoors, although they used kangaroo skin cloaks in cold weather. They did get some way down the road towards agriculture in places though. They remained migratory with the seasons, although not migrating large enough distances to make a big difference in the amount of UV exposure they got in winter - they were moving to seasonal hunting and gathering grounds, not chasing the sun.

It's a bit of a puzzle.

By Sandgroper (not verified) on 07 Dec 2007 #permalink

Sandgroper,

I remember reading that 95% of Australian aboriginal languages are closely related - pama-nguyan group - and seem to have had a common ancestor language only 5,000 years ago - it has been postulated that they received an influx of people from Southern India around this time, and this may be related to the spread of this language group.

So it's possible that they were lighter pigmented previously, if they don't have a ready source of vitamin D in their diets?

Isn't it more likely that lack of UV was due to development of clothing? Even today (during an interglacial) only the summer months are warm enough to go about naked.

that is likely part of it. but, note that inuit wear a lot of clothing but aren't that light-skinned (they get their D from marine animals). additionally, it seems that humans have gotten lighter skinned in eurasia as the temperatures increased. that is, they were darker-skinned when they had to wear clothing more obligately.

I remember reading that 95% of Australian aboriginal languages are closely related - pama-nguyan group - and seem to have had a common ancestor language only 5,000 years ago - it has been postulated that they received an influx of people from Southern India around this time, and this may be related to the spread of this language group.

i think the balance of the genetic data implies deep time history for aboriginals. there is no chance that most of their ancestry came from southern india (or greater south asia) in the last 5,000 years. the genes and languages seem too different. there would some migration or exchange though, the dingo came in the last 10,000 years.

Raz,

I mean in the same way that NorthWest Cameroon has a pocket of R1b* Y-DNA - whose highest world concentration is in Jerico - indicating a back migration from the Middle East, and possibly the introduction of agriculture. This area is also the start point of the Bantu Expansion, and is responsible for the fact that the bulk of sub-saharans speak a Bantu dialect.

I wonder if there was a similar episode with Southern Indians - veddoids - in Australia - in that a fairly small influx, with some competitive advantage, led to a replacement of male Y-DNA in Australia, and spread of a particular language group??

Sandgroper: "There are big differences in UV radiation with latitude, especially in winter."

Yes, but at annual level the differences aren't that big. I would expect that the genetic part of pigmentation would depend on annual average rather than darkest season. Otherwise the sun tan effect would be much bigger.

Here's a monthly map of weather-corrected sunshine in modern times:
http://www.sureguard.com.au/solaranimationww.html

Amount of UV doesn't seem to correlate very well with skin colour. Note especially that "black" Africa gets about as much UV as the Mediterranean coast only a thousand kilometres away, but still the skin colours are quite different. It can't be explained with migrations alone, because many Mediterraneans have been moving only east-west during latest several millennia.

Of course that map isn't accurate for the Ice Age, because global climate was different then. Unfortunately I don't know of any weather-corrected estimates of UV in those days.

By Lassi Hippeläinen (not verified) on 08 Dec 2007 #permalink

Amount of UV doesn't seem to correlate very well with skin colour.

it correlates OK. e.g., The major results of this study are: (1) skin reflectance is strongly correlated with absolute latitude and UV radiation levels. The highest correlation between skin reflectance and UV levels was observed at 545 nm, near the absorption maximum for oxyhemoglobin, suggesting that the main role of melanin pigmentation in humans is regulation of the effects of UV radiation on the contents of cutaneous blood vessels located in the dermis. (2) Predicted skin reflectances deviated little from observed values. (3) In all populations for which skin reflectance data were available for males and females, females were found to be lighter skinned than males. (4) The clinal gradation of skin coloration observed among indigenous peoples is correlated with UV radiation levels and represents a compromise solution to the conflicting physiological requirements of photoprotection and vitamin D synthesis.

read this paper for the math.

Lassi,

Think seasonally or even monthly. Sometimes fitness can change after a few days. An aggressive bacterium such as Tuberculosis will take advantage of even a slight reduction in immune function. It may take years for the TB to kill the patient, but a weakening of the immune system can take only days with low levels of Vitamin D.

Thanks, Razib.

At least that confirms my subjective observation that skin colours of northern Africa don't match the UV levels. Algerians and Libyans are too light, while Nigerians are too dark. That could be connected with the cultural issues, i.e. the Mediterranians wear clothes. And females being lighter... they probably spend more time indoors.

BTW, Fig 3 predicts skin colour using *annual* averages of UV. Short time effects of vitamin D must also consider other sources, e.g. food. Here in Fennoscandia fish is easily available in the dark winter months, because then you can go ice fishing. Or hunt seals from the ice.

By Lassi Hippeläinen (not verified) on 08 Dec 2007 #permalink

That could be connected with the cultural issues, i.e. the Mediterranians wear clothes.

the light skin of north africa and the middle east might be recent. SLC24A5 has very high selection coefficients within the last 6,000 years in this region, going from 0 to fixation.

And females being lighter... they probably spend more time indoors.

no, this is wrong. the skin reflectance difference is found in unexposed areas (underarm). probably it is due to the interaction between melanin production pathways and hormone levels (women get darker as they age, and are lightest during adolescence).

As an afterthought, why didn't I mention buildings as well as clothing? All Mediterranean cultures spend siesta. When the Sun is hitting them hardest, they retreat under a roof, or at least in the shade of a tree. So the solar irradiation models won't predict correctly how much UV they get in real life.

Just made me wonder how long and how widely siesta has been observed...

By LAssi Hippeläinen (not verified) on 10 Dec 2007 #permalink