red hair and gloom -- 9/1/15
Today's selection -- from Red: A History of the Redhead by Jacky Collis Harvey. Red hair and pale skin conferred a genetic benefit in Northern climates:
"The gene that today results in the red hair of almost every redhead on the planet sits on chromosome 16, and if you have red hair, it's because the version you have of that gene is not working as well as it might. Working perfectly, that MC1R gene, or melanocortin 1 receptor, to give it its full name, would give you brown eyes, dark skin, and an ability to withstand strong sunlight without developing sunburn, sunstroke, or worse. It would do this by stimulating the production of a substance called eumelanin, which colors dark skin, dark eyes, and dark hair. However, MC1R is fritzy. Like a bad internet provider, it flips in and out. If you have red hair, it is almost certainly (there are rare medical conditions that produce red hair, and in the Solomon Islands in the Pacific, an entirely different genetic mutation gives some islanders the most striking gingery-blond afros) almost certainly, therefore, down to the fact that you carry two copies of a specific recessive variant of the MC1R gene that dials eumelanin production (with all its protective benefits under strong sun) right down, replacing it with yellow or red phaeomelanin, in an extraordinarily complex set of variants that determines the color of individual hairs on your head and of individual cells in your skin.
"MC1R, however, is not alone in this process. There is another gene, HCL2, on chromosome 4 (rather unpoetically, HCL2's full name is simply 'hair color 2 [red]'), that also contributes to red hair. Moreover (I did warn you this was complex), while red hair is indeed caused by a recessive gene, there are many possible variants, from recessive red to fully dominant brown or black, with an equal number of manifestations of so-called 'codominance' in between. ... In general, redheads and strong sun most emphatically do not mix. ... [In Europe] the incidence of red hair drops off below that forty-fifth line of latitude. ...
"It may be going too far to characterize Mother Nature as smart, but left to herself she does have a heartlessly effective way of cleaning out the gene pool. If you're not fit to survive, you won't. But if a genetic quirk confers a benefit upon those carrying that gene, it, and they, will flourish. And pale skin under Northern skies does exactly that. If your eumelanin production is dialed back, if you have pale skin rather than dark, your body will be much more effective at synthesizing vitamin D, using whatever sunlight is available, than if your skin were darker. And as the ice sheets retreated, and that growing population of early modern humans moved from Russia into Scandinavia, and eventually into the whole of northern Europe, the absence of strong sun in these climes allowed the MC1R gene to mutate into what geneticists term 'dysfunctional variants' without these variants proving fatal to those carrying them. In fact the farther north this population went, the more advantageous pale skin became. If you have enough vitamin D, your skeleton develops as it should. If you do not, your bones are soft and stunted, and as you learn to walk, your legs bow under your weight. This is osteomalacia, or rickets. In adults, it causes calcium to leach away from your bones; in children, it cripples you. Women of child-bearing age who suffered from rickets when they themselves were children have distorted pelvises that make carrying a pregnancy to full term difficult and childbirth hazardous, if not fatal.
"Communities that eat most of their protein in the form of meat, as with the early hunter-gatherers, rarely suffer from vitamin D deficiency. But the tendency in the early modern human population was to settle; to become farmers, to grow and eat grain. In these circumstances, pale skin helped keep you strong and healthy. In particular, it gave a significant advantage to women during pregnancy and breast-feeding, when their bodies' demand for vitamin D was at an all-time high, which along with all the other ancient and instinctive associations of the color red (fire, blood, passion, ripeness) does rather open the question as to whether the often highly sexualized image of female redheads might not start here, with the simple fact that choosing a redhead as a mate meant you bred successfully, and that your pale-skinned children, themselves now carrying the gene for red hair, did the same."