One of the problems with using a trait like hair color to try to
trace population movements is precisely that various types are each
advantageous in some environments and detrimental in others, thus
subject to natural selection. That can seriously skew the findings.
Generally geneticists try to find a variation which is neutral in
regard to natural selection.

Regards,
Ned Smith

--- In Nostratica@yahoogroups.com, "John" <jdcroft@...> wrote:
> If Afro-Asiatic languages evolved in Africa (as is commonly
thought)
> and is the most distantly related Nostratic tongue, it is quite
> possible that Proto-Nostratic appeared first in Africa, before
> crossing into the Middle East - creating another centre for
dispersal
> in Northern Mesopotamia, and the Zagros-Taurus "knot" region (as
> suggested by Bomhard).
>
> On another topic I was researching the genetics of human hair
> colouration and realised that it can show us quite a lot on human
> movements that relate to the spread of Nostratic, Afro-Asiatic and
> PIE languages.
>
> Genetically the situation is complex. Hair colour is a matter of
> melanin synthesis pathway. Generally there are two types of melanin
> present eumelanins and pheomelanins. The eumelanin is black in
> colour and made from processing the amino acid tyrosine into dopa
and
> dopamine in the presence of tyrosinase, and then joining a number
of
> these chains together to form the eumelanin. Generally eumalinin is
> brown (with 2 polypeptide chains and a COOH acid radical), but with
> more tyrosinase present it will be dark black in colour (with 3
> polypeptide chains). Pheomelanins are produced also as a result of
> tyrosinase when an intermediate product in the eumelanin production
> pathway interacts with the amino acid cysteine. This results in the
> formation of a pheomelanin molecule which contains sulfur from the
> cysteine. These molecules are yellow to orange in color. Black
> haired people have both eumelanins and pheomelanins present. Blond
> haired people have a blockage on the pathway that leads to
eumelanin
> expression, allowing pheomelanins to be expressed by themselves.
Red
> haired people have a gene which causes clumping of the eumelanins,
> and an expression of the pheomelanins.
>
> Amongst Europeans and people of North Africa and the Middle East
> there are four main types of genes governing these processes, which
> are dominant, recessive, incomplete dominant, and co-recessive.
Here
> are the more common common hair colors for the human
> genome.
>
> Dominant.............Black (B), or Brown (Br)
> Recessive............Blond (b)
> Incomplete Dominant..Red (R)
> Co-recessive.........other blonds (db)
>
> This suggests that amongst the Europeans the gene for blondness
> evolved twice (b) and (db) whilst the gene for red hair (R) evolved
> once. Red hair generally is associated with the clumping of
> eumelanins, allowing the underlying pheomelanins to be expressed.
> The clumping also is requently expressed in freckles. This
freckling
> makes the skin especially prone to skin cancers in the presence of
> ultraviolet light.
>
> As human beings, we receive two genes for hair color, one from the
> mother, and one from the father. However, depending on the type of
> gene we receive, we can either inherit one color over another
> (dominant over recessive, which leaves the recessive present but
> inexpressed), or a blending of the two.
>
> Being an incomplete dominant gene, the Red R gene will frequently
> show an appearance with black (B), brown (Br) or blond hair (b) or
> (db) genes having a redish tinge.
>
> Looking at this within a framework of the history and geography of
> the human genome leads to interesting results. We find that
> generally blondness and red haired people are at a genetic
> disadvantage - they suffer increased rates of melanomas when
exposed
> to ultra-violet. Thus there has to be another corresponding genetic
> advantage offered to explain their expression.
>
> In fact there are two advantages.
>
> 1. In hot dry environments, blond hair reduces the chance of
> heatstroke. This seems to have been a factor in desert environments
> and seems to explain the (db) incomplete co-recessive gene. It
seems
> to have been evolved in the Sahara, being carried into the Middle
> East at least twice - once with the movement of people across the
> Palestinian land bridge 15,000 BCE (the so-called Nostratic
> movement?), the second circa 6,000 BCE, with the movement of Afro-
> Asiatic speaking Semites (?) into Asia from Africa. This by the way
> explains the appearance of blondness amongst Australian Aborigines
> (where a different genetic mutation altogether is involved). Blond
> Aborigines are found more commonly in the Central Desert regions of
> the country.
>
> 2. In cloud covered areas where diets are deficient in meat, and
> especially in regions where grains or starches are the staple, the
> presence of eumelanins prevents the absorption of sufficient
> ultraviolet light to make vitamin D and rickets results. This was
> especially so in the first farming communities spreading into
Europe
> from the Middle East. In such circumstances, mutations which
prevent
> the expression of eumelanins will be favoured - encouraging the
> spread of the R gene (probably first from the Balkans and Central
> Europe), and secondly of the b gene, appearing first in the Ukraine
> and subsequently moving east and west across the steppes. This by
> the way is also the reason for blond hair in the highlands of Papua
> New Guinea, where again a completely different mutation seems to be
> involved, often producing a similar clumping of eumelanins to the R
> gene.
>
> Dating these different mutations can also be read from the human
> genome. It appears that the B and Br genes have been with human
> populations since we left Africa, at least 73,000 years ago. The bd
> gene appeared possibly 25-30,000 years ago, and probably in the
> Sahara. Both R and b genes are the youngest, appearing between 8
and
> 5,000 years ago and probably not in the Middle East, but in Europe.
>
> Of course subsequent human migrations, of Indo-Europeans into
> Anatolia, and of Mitannite Indo-Aryans throughout Mesopotamia and
> Palestine, has really mixed matters further, so that all areas are
> today highly hybridised.
>
> There is a huge bibliography available on the biology and
> distribution of hair colouration, which I will not go into here,
but
> I can dig out much if people are interested in hair biochemistry.
>
> Hope this helps
>
> Regards
>
> John