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Saturday, February 02, 2013

Vitamin D in Prehistory

  When considering the effect on health of vitamin D I thought of a reverse way of finding it.

  The gene for light skin evolved 50,000 years ago (we can tell by the amount of chnge in the "junk" sections of the DNA.

  That means that in roughly 2,000 generation (or less, pehaps much less) it has spread from its originator to the entire European continent and more.

   If we take that as a millionfold increase (actually considerably more but at the time of the first evolution Europe's population was probably under a million) we can take the bonus in each generation, that is for each next generation, as the root to the power 2,000 of 1 million.

     1.069   or a 0.69% evolutionary advantage.

     Remember not only that this is a minimum but that throughout almost all of this period life was far shorter and more dangerous than now. Prostate cancer, when sabre tooth tigers were around, was not the major threat it is now.

      Moreover this is not how it affects individual's longevity but only how it affects them while they are still bringing up children.

      Taking both of those intom account it seems to me that the effect on mortality now cannot reasonably be taken as less than 2.8% (0.69 X 4), though it may well be much larger.

       This is the benefit of having white skin at average European latitudes, In Scotland we already have white skin but

    "Scotland receives 30-50% less ultraviolet radiation (UVB) from the sun than the rest of the UK due to its high latitude and persistent low cloud cover. Vitamin D levels are consistently found to be even lower in Scotland than the rest of the UK. (168)(165)(166) (167)

Indeed, Glasgow, with one of most cloudy climates receives a similar amount of UVB as Kiruna in Northern Sweden which is way above the Arctic Circle"

    Which suggests excess mortality of Scots should be comparably greater than that of the European average - and we have no evolutionary mutation to help us.

    Ending 2.8% of mortality may not be spectacular for society as a whole but it is a hell of a lot of people.

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"and we have no evolutionary mutation to help us": unless that's what the ginger hair is about.
That sounds quite likely - the Brotherhood of Red Headed Mutants - all with paerticularly peelywally sjins. However I can't see a secondary mutation like that being nearly as useful as the change from black to "white" skin. On the 3rd hand if it still spread, despote being say half as effective it would suggest vitamin d was twice as important as i thought.

Thanks, I'll look into it.
I'm not ginger, though I have a ginger cousin. The hair on my arms glows copper-gold in the sun (copyright my wife), and my long gone sideburns had a pronounced ginger tinge.

It's odd that there's no word for people with just hints of ginger.
My beard used to be distinctly red and the rest brown with a hint of red. However [people seeing me from the front took that as a gestalt red.

Unfortunately both are now very light blond :-)
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