Indian populations are composed of two ancestral components: Ancestral North Indians (ANI) and Ancestral South Indians (ASI), discovered by Reich et al. (2009). In that paper, it was also shown that ASI forms a clade with East Eurasians, while ANI does so with West Eurasians.
![]()
Consider the following D-statistic:
As we shall see, this takes positive values, consistent with the idea of gene flow between Europeans and Indians at the exclusion of Sardinians. However, this gene flow may involve either the West Eurasian component in the ancestry of Indians (i.e., this component is more related to Europeans than to Sardinians), or to the ASI component (which is related to Europeans via the common "red arrow" portions of ancestry).
We can figure out what is going on by trying different Indian populations along the Indian Cline, and seeing whether the D-statistic is inflated/deflated in populations of greater ANI/ASI ancestry.
Here are the results:
Russian Orcadian French Lithuanians ANI
Mala 0.0153 0.0120 0.0088 0.0131 38.86
Madiga 0.0153 0.0122 0.0091 0.0111 40.66
Chenchu 0.0157 0.0108 0.0088 0.0115 40.76
Bhil 0.0149 0.0115 0.0086 0.0124 42.96
Satnami 0.0166 0.0125 0.0091 0.0126 43.06
Kurumba 0.0156 0.0117 0.0095 0.0121 43.26
Kamsali 0.0139 0.0105 0.0088 0.0098 44.56
Vysya 0.0130 0.0099 0.0083 0.0102 46.26
Lodi 0.0143 0.0124 0.0092 0.0125 49.96
Naidu 0.0138 0.0104 0.0092 0.0108 50.16
Tharu 0.0150 0.0112 0.0095 0.0118 51.06
Velama 0.0126 0.0107 0.0083 0.0095 54.76
Srivastava 0.0144 0.0124 0.0091 0.0116 56.46
Meghawal 0.0131 0.0107 0.0088 0.0117 60.36
Vaish 0.0143 0.0144 0.0099 0.0128 62.66
Kashmiri_Pandit 0.0119 0.0116 0.0090 0.0116 70.66
Sindhi 0.0106 0.0112 0.0095 0.0111 73.76
Pathan 0.0098 0.0114 0.0087 0.0106 76.96
![]()
![]()
![]()
![]()
In other words, the evidence for gene flow between Russians and Indians is maximized when south Indian (ASI-rich) populations are used.
![]()
![]()
Patterson et al. (2012) published a different pattern: non-Sardinian Europeans have North Eurasian-like ancestry that links them to Amerindian populations. It is thus possible that ASI and the East Eurasian-like admixture in North Europeans may share a common evolutionary history:
Now, consider a hypothetical population of the Indian Cline. A European population is related to it both via its ANI/West Eurasian ancestry, but also via its ASI ancestry, because the East_Eurasian component in Europeans shares a portion of ancestry (indicated by the red arrow) with ASI.
Sardinians lack (or have less of) this "red arrow" portion of ancestry.
It is also possible that ANI itself may have some East_Eurasian ancestry, like Europeans do; this is not indicated in the figure. More on this later.
D(European, Sardinian, Indian, San)
As we shall see, this takes positive values, consistent with the idea of gene flow between Europeans and Indians at the exclusion of Sardinians. However, this gene flow may involve either the West Eurasian component in the ancestry of Indians (i.e., this component is more related to Europeans than to Sardinians), or to the ASI component (which is related to Europeans via the common "red arrow" portions of ancestry).
We can figure out what is going on by trying different Indian populations along the Indian Cline, and seeing whether the D-statistic is inflated/deflated in populations of greater ANI/ASI ancestry.
Here are the results:
Russian Orcadian French Lithuanians ANI
Mala 0.0153 0.0120 0.0088 0.0131 38.86
Madiga 0.0153 0.0122 0.0091 0.0111 40.66
Chenchu 0.0157 0.0108 0.0088 0.0115 40.76
Bhil 0.0149 0.0115 0.0086 0.0124 42.96
Satnami 0.0166 0.0125 0.0091 0.0126 43.06
Kurumba 0.0156 0.0117 0.0095 0.0121 43.26
Kamsali 0.0139 0.0105 0.0088 0.0098 44.56
Vysya 0.0130 0.0099 0.0083 0.0102 46.26
Lodi 0.0143 0.0124 0.0092 0.0125 49.96
Naidu 0.0138 0.0104 0.0092 0.0108 50.16
Tharu 0.0150 0.0112 0.0095 0.0118 51.06
Velama 0.0126 0.0107 0.0083 0.0095 54.76
Srivastava 0.0144 0.0124 0.0091 0.0116 56.46
Meghawal 0.0131 0.0107 0.0088 0.0117 60.36
Vaish 0.0143 0.0144 0.0099 0.0128 62.66
Kashmiri_Pandit 0.0119 0.0116 0.0090 0.0116 70.66
Sindhi 0.0106 0.0112 0.0095 0.0111 73.76
Pathan 0.0098 0.0114 0.0087 0.0106 76.96
For each Indian Cline population, I list the ANI percentage, as estimated by Reich et al. (2009) in the last column, and the D-statistic of the above given form for different pairs of Indian and European populations.
We can plot the D-statistic vs. ANI for each of our European populations:
The correlation coefficients confirm the visual impression, that for the HGDP Russians there is a significantly negative relationship between ANI admixture in an Indian Cline population and the D-statistic:
Russian Orcadian French Lithuanians
-0.8631118 0.08670188 0.1870127 -0.1889908
In other words, the evidence for gene flow between Russians and Indians is maximized when south Indian (ASI-rich) populations are used.
The lack of a clear pattern in the other three populations is itself interesting. One possible explanation involves East Eurasian-like admixture in the ANI, a conjecture which would make sense, given that all non-Sardinian continental West Eurasians seem to possess it.
If that is true, then as we go "south" along the Indian Cline, ASI related admixture inflates the D-statistic by increasing the "red arrow" overlap with the East Eurasian-like admixture in Europeans. As we go "north" along this cline, then the D-statistic decreases, due to ASI-reduction, but also increases, due to East Eurasian-like admixture in ANI, with an end result of no clear pattern in the superposition of processes.
In any case, this is an interesting example of a crisscrossing type of admixture where unrelated processes (east Eurasian-like admixture in Russians and ASI admixture in Indians) combine to present an unusual effect.
If that is true, then as we go "south" along the Indian Cline, ASI related admixture inflates the D-statistic by increasing the "red arrow" overlap with the East Eurasian-like admixture in Europeans. As we go "north" along this cline, then the D-statistic decreases, due to ASI-reduction, but also increases, due to East Eurasian-like admixture in ANI, with an end result of no clear pattern in the superposition of processes.
In any case, this is an interesting example of a crisscrossing type of admixture where unrelated processes (east Eurasian-like admixture in Russians and ASI admixture in Indians) combine to present an unusual effect.
