In human evolution, changes in skin's barrier set Northern Europeans apart

Jun 30, 2014 by Jeffrey Norris
Human Skin

The popular idea that Northern Europeans developed light skin to absorb more UV light so they could make more vitamin D – vital for healthy bones and immune function – is questioned by UC San Francisco researchers in a new study published online in the journal Evolutionary Biology.

Ramping up the skin's capacity to capture UV light to make vitamin D is indeed important, according to a team led by Peter Elias, MD, a UCSF professor of dermatology. However, Elias and colleagues concluded in their study that changes in the skin's function as a barrier to the elements made a greater contribution than alterations in skin pigment in the ability of Northern Europeans to make vitamin D.

Elias' team concluded that compromising the skin's ability to serve as a barrier allowed fair-skinned Northern Europeans to populate latitudes where too little ultraviolet B (UVB) light for vitamin D production penetrates the atmosphere.

Among scientists studying human evolution, it has been almost universally assumed that the need to make more vitamin D at Northern latitudes drove genetic mutations that reduce production of the , the main determinant of skin tone, according to Elias.

"At the higher latitudes of Great Britain, Scandinavia and the Baltic States, as well as Northern Germany and France, very little UVB light reaches the Earth, and it's the key wavelength required by the skin for vitamin D generation," Elias said.

"While is seems logical that the loss of the pigment melanin would serve as a compensatory mechanism, allowing for more irradiation of the skin surface and therefore more vitamin D production, this hypothesis is flawed for many reasons," he continued. "For example, recent studies show that dark-skinned humans make vitamin D after sun exposure as efficiently as lightly-pigmented humans, and osteoporosis – which can be a sign of vitamin D deficiency – is less common, rather than more common, in darkly-pigmented humans."

Furthermore, evidence for a south to north gradient in the prevalence of melanin mutations is weaker than for this alternative explanation explored by Elias and colleagues.

In earlier research, Elias began studying the role of skin as a barrier to water loss. He recently has focused on a specific skin-barrier protein called filaggrin, which is broken down into a molecule called urocanic acid – the most potent absorber of UVB light in the skin, according to Elias. "It's certainly more important than melanin in lightly-pigmented skin," he said.

In their new study, the researchers identified a strikingly higher prevalence of inborn mutations in the filaggrin gene among Northern European populations. Up to 10 percent of normal individuals carried mutations in the filaggrin gene in these northern nations, in contrast to much lower mutation rates in southern European, Asian and African populations.

Moreover, higher filaggrin mutation rates, which result in a loss of urocanic acid, correlated with higher vitamin D levels in the blood. Latitude-dependent variations in melanin genes are not similarly associated with vitamin D levels, according to Elias. This evidence suggests that changes in the skin barrier played a role in Northern European's evolutionary adaptation to Northern latitudes, the study concluded.

Yet, there was an evolutionary tradeoff for these barrier-weakening filaggrin mutations, Elias said. Mutation bearers have a tendency for very dry skin, and are vulnerable to atopic dermatitis, asthma and food allergies. But these diseases have appeared only recently, and did not become a problem until humans began to live in densely populated urban environments, Elias said.

The Elias lab has shown that pigmented skin provides a better barrier, which he says was critically important for protection against dehydration and infections among ancestral humans living in sub-Saharan Africa. But the need for pigment to provide this extra protection waned as modern human populations migrated northward over the past 60,000 years or so, Elias said, while the need to absorb UVB light became greater, particularly for those humans who migrated to the far North behind retreating glaciers less than 10,000 years ago.

The data from the new study do not explain why Northern Europeans lost melanin. If the need to make more vitamin D did not drive pigment loss, what did? Elias speculates that, "Once human populations migrated northward, away from the tropical onslaught of UVB, pigment was gradually lost in service of metabolic conservation. The body will not waste precious energy and proteins to make proteins that it no longer needs."

For the Evolutionary Biology study, labeled a "synthesis paper" by the journal, Elias and co-author Jacob P. Thyssen, MD, a professor at the University of Copenhagen, mapped the mutation data and measured the correlations with blood levels of vitamin D. Labs throughout the world identified the mutations. Daniel Bikle, MD, PhD, a UCSF professor of medicine, provided expertise on D metabolism.

Explore further: Mutation V60L increases predisposition to skin cancer

More information: Evolutionary Biology, link.springer.com/article/10.1… %2Fs11692-014-9282-7

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Shootist
not rated yet Jun 30, 2014
Don't know about any of the above, but that does nothing to change the fact that Caucasians have one set of genes controlling the lightening while East Asians have a different set of genes that accomplish the same task. These genes are not apparent in Sub-saharan Africans or Native Australians. These genetic differences are indicative of the environmentally driven evolution and divergence of H. Sapiens.
tadchem
not rated yet Jun 30, 2014
"...changes in the skin barrier played a role in Northern European's evolutionary adaptation to Northern latitudes, the study concluded."
That much has never been contested.
"At the higher latitudes of Great Britain, Scandinavia and the Baltic States, as well as Northern Germany and France, very little UVB light reaches the Earth, and it's the key wavelength required by the skin for vitamin D generation," Elias said.
So the northern peoples with lighter, more mutated skin are not able to produce sufficient Vitamin D to maintain good health? That means they must be getting their Vitamin D in their diet, from mushrooms, beef liver, fish and fish oils, and from a (coincidentally) mutated gene for the enzyme that inhibits lactase activity, allowing consumption of Vitamin D-rich dairy (often from cow's milk) well past weaning.
tekram
1 / 5 (3) Jun 30, 2014
Re: "The data from the new study do not explain why Northern Europeans lost melanin. If the need to make more vitamin D did not drive pigment loss, what did? Elias speculates... metabolic conservation "

So this guy pulls a theory out from where the sun don't shine? Well, maybe he is over thinking this. Why did the polar bear lost its hair pigmentation? The polar bears are clearly not albinos and neither are most northern Europeans, but both were apex predators a few thousand years ago.
Torbjorn_Larsson_OM
5 / 5 (2) Jun 30, 2014
Now that makes a lot of sense!

The melanin genes are under selection, while the tanning response isn't. [ http://en.wikiped...in_color ] Which means that it doesn't much matter how fast you protect yourself against UVB, the benefits and harm is with very little exposure. Indeed, ~ 15 minutes/day of sun is enough.

That metabolic conservation is a driver for the former. for initial light-skin irrespective of tanning response, suits.
Torbjorn_Larsson_OM
5 / 5 (2) Jun 30, 2014
@tadchem: Usually sunlight is the main D vitamin source at all locations AFAIK.

It is only if you get to the latitudes where sunlight is restricted to a few hours that you start to get benefits from food supplements as then periods of bad weather may be restricting UVB exposure.

@tekram: That is an interesting idea. But both the hunter-gatherers (that indeed where the most melatonin-poor, see the surviving Samis and Finns) and the agrarians (Indo-Europeans) are melatonin-poor.

I don't think we know enough to resolve the details yet. E.g.: "a 2014 analysis of mesolithic (7,000 years old) hunter-gatherer DNA from La Braña, Spain, which showed the version of these genes corresponding to dark skin color." [http://en.wikiped...in_color ] If the oldest europeans (with rest populations Samis & Finns) are now lightest on average, why would they have been dark before the indo-european invasion?
JVK
1 / 5 (5) Jun 30, 2014
Like other morphological and behavioral phenotypes in other species, skin pigment varies with ecological variation and is controlled by the physiology of reproduction. Attributing skin pigment differences to mutations and natural selection in the context of the evolution of biodiversity is a leftover from the invention of neo-Darwinism by population geneticists who still seem unable to grasp how the epigenetic landscape becomes the physical landscape of DNA in the organized genomes of species from microbes to man.
marcush
5 / 5 (3) Jul 01, 2014
Sorry JVK, I don't get it. Why do morphological and behavioural phenotypes vary with ecological variation and what has the physiology of reproduction got to do with it? Are you trying to say that skin colour is epigenetic? I don't think that's the case.
JVK
1 / 5 (3) Jul 01, 2014
http://www.pnas.o...abstract links epigenetics of nutrient uptake to morphological and behavioral phenotypes via my detailed model of cell type differentiation, which theorists would like you to believe is driven by mutations and natural selection. http://figshare.c...s/994281
etherair
not rated yet Jul 04, 2014
All the article mentions is northern European light skin. My family is northern North American of similar latitude but much darker skin than the Europeans. Kinda fits in with their conclusions though.
Studies do show a lower Folic acid and vitamin D serum concentrate than similar peoples from further south. The reproductive rates are maintained even with this difference, indicating this is not a major factor driving the skin tones.
russell_russell
not rated yet Jul 05, 2014
LIght is food? O.k. If you say so.
Anyway, different sets of genes harbor the potential to have the same switches (translations).
OM is spot on. Enjoy him understanding this. I do.