Mohd Fareed has provided the sample sizes for each degree of relatedness, and an explanation for the larger number of first cousin marriages, which is the cultural norm in those communities. I have added in, from his paper with Mohammad Afzal, the degree of relatedness for each group and the mean IQ and standard deviations. The results are intriguing.
n Relatedness IQ sd
Non-inbred 225 .0000 96.51 (16.25)
Second cousin 31 .0156 88.57 (13.99)
First cousin once removed 21 .03125 79.70 (6.51)
First cousin 105 .0625 68.72 (7.15)
Double first cousin 26 .125 59.52 (14.99)
Mohd says: Now a question may arise in the mind of the public, why aren’t the sample sizes uniform? The answer is: among Muslims, first cousin marriages constitute about 70% or even more of marriages, as compared to the other inbred categories.
Anyway, let me get stuck into these results, which are the sort of statistics I can understand. First cousins, the most numerous in the sample by far, have half the normal standard deviation, as do first cousins once removed. Why? The first cousin result cannot be a small sample size problem. Why this massive restriction in variation? Second cousins and double first cousins have the normal variation. Why? Variance reduces with degree of inbreeding and then bounces back again for the most inbred. Why? I can think of a possible psychometric hypothesis, suggested to me by an esteemed person of my acquaintance, but I haven’t got round to reading all the textbooks on population genetics kindly recommended to me by distinguished scholars (extremely expensive books, by the way) so could population geneticists please help?
That perplexing problem aside, the IQ for the entire inbred category comes out at IQ 72. The “marry your cousin” meme reduces the average IQ by almost 2 standard deviations. Cruelly, these believers will have been cast into such a state of mental weakness that convincing them of the downside of cousin marriage may take a long time, Bollywood notwithstanding.
If we put together the 225 outbred with the 183 inbred we get an overall IQ of 85.5. Given that Lynn’s mean value for India is about 82, Pakistan about 84 these results are within measurement error, and closer to the Pakistan figures. Lynn’s lists are not complete, and need updating,(he does the job himself, without any funds of the sort that PISA commands) but they are given below for comparison anyway.
In summary, this sample seems very much like the other samples from India and Pakistan in terms of mental ability. What seems clear is that to get an understanding of the potential underlying ability we need to make a massive allowance for inbreeding. Scores of about IQ 96 should be possible in outbred groups.
To understand the regional social and political behaviours as they are at the moment, we need to understand that there are two tribes in contention: higher status outbreeds of average IQ 96, with considerable freedom from their cousins; and lower status inbreeds of average IQ 72, condemned by chains of obligation to perpetual, uncomprehending cousinhood.
Now, as Mohd Fareed says, Muslim India is not the only part of the world that encourages cousin marriage, but I hope that altruists not yet bound for West Africa could give Fareed and Azfal a call, to see if they can give them a hand with genetic counselling materials, training genetic councillors, and working with local researchers and activists to change the cultural meme of arranged cousin marriages. Better still, if you are a Hollywood actor or director, why not Tweet them now, or if that is too much effort, get your people to send their people a cheque?
Summary data from Lynn.