Note:
1. Aryan invasion is not accepted by the Academia. It is Aryan
migration theory.
2. Current Indian population was shaped by four major migrations,
so everyone is a mix.
3. The accepted major migrations are : Out of Africa
migrations(South Asian hunter gatherers), Proto Dravidian migrations,
Austroasiatic migrations (Mundas, Khasis) , Steppe migrations (Aryans)
4. Aryan migration or the Steppe migration was largely responsible
for the introduction of a light skin allele now found throughout the sub-continent.
To understand how Aryans
introduced the light skin allele to the Indian sub-continent:
Geneticists propose that as
humans started to colonize higher latitudes, where Ultra
violet radiation levels were lower, dark skin could not absorb
sufficient UVR for efficient vitamin D synthesis, hence natural selection favoured
the evolution of light skin.
One of the key pigmentation genes
in humans is SLC24A5.
An allele of this gene rs1426654 explains
25–38% of the skin colour variation between Europeans and West Africans.
The ancestral (rs1426654-
G) allele of the SNP predominates in African and East Asian
populations (93–100%),
Whereas the derived
(rs1426654 - A) allele is almost fixed in Europe (98.7–100%)
A recent study showed that the
light skin associated allele in South Asians is identical by descent to
that found in Europeans. [1]
The study found that rs1426654-A
allele is responsible for light skin in Indians.
Frequency of SLC24A5 among
global populations:
In short:
Early Humans were all dark.
When humans first moved out of
Africa and colonized higher latitudes, they developed light
skin.
The Gene responsible for light
skin is SLC24A5
A variation of an allele of this
gene rs1426654-A is responsible for light skin in Europeans
and South Asians.
The ancestral allele rs1426654-G is
predominantly found in Africans and East Asians.
The study found that Indo
Aryan speakers have the highest percentage of this allele.
The Light skin Allele is high
in Northern and North-western regions and virtually absent in NE India :
The study also found that there
is a general trend of rs1426654-A allele frequency being higher in the
Northern (0.70±0.18) and North-western regions (0.87±0.13), moderate
in the Southern (0.55±0.22), and very low or virtually absent in North-eastern
populations of the Indian subcontinent
They found that the rs1426654-A
allele frequency in South Asia does not significantly correlate with
latitude (r = 0.23, p = 0.15).
However, a significant negative
correlation with longitude (r = −0.49; p = 0.002) was observed.
The Map shows the distribution
of the Allele rs1426654-A :
They found that the Tibeto-Burman
and the Austroasiatic language families have the lowest frequencies of the A
allele.
The rs1426654-A allele frequency
was significantly higher in Indo-European speakers than in
other language groups.
In particular, there was a
significant difference (p<0.001) between the A allele frequencies of
the Indo-European and the Dravidian speaking groups.
They found that both language and
geography have a significant influence on rs1426654-A allele frequency, as
revealed by Mantel tests (p<0.001).
To make it simple:
Humans who settled in Eurasia
evolved to have rs1426654-A allele
When the steppe migrations
happened they brought this allele into Indian subcontinent.
Indo Aryan speakers have the
highest percentage.
There was significant difference
in the percentage of this A allele, between Indo Aryan speakers and Dravidian
speakers.
Austroasiatic speakers and Tibeto-Burman
speakers have the lowest percentage of this allele.
To have a rough idea of how these
early populations might have looked:
The proxy for Indo Aryans: According
to
The Modern Indian
Cline intersects the Steppe Cline at a position close to
the position of the Kalash, the group in northwest South Asia with the
highest ANI ancestry proportion.
So, Kalash tribes are a proxy for
Indo Aryan populations:
So the first Steppe migrants
might have looked like this.
The Proxy for South Asian
hunter gatherers are the Irulas:
The SHG populations would have
had skin pigmentation close this:
Austroasiatic populations: the
Mundas:
Footnotes [1] The Light Skin Allele of SLC24A5 in South Asians and Europeans Shares Identity by Descent
No comments:
Post a Comment