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.