Indian Ancestry on Nature's cover. Awesome!

I just got this week's Nature magazine. (Yes, I have a personal subscription. There are copies of Nature and Science on my TV tray. Yes, I am a dork.)

And this is what is on the cover:

The actual article by Reich, Thangaraj, Patterson, Price and Singh (and a really neat "News and Views" section written by Aravinda Chakravarti at Hopkins) basically looks at the variation in genomes of individuals from India. Without getting into the weeds, what they did was to analyze DNA from 25 different groups in India, from different geographical areas, from different castes and language groups, and then do some statistical heavy lifting to look at how similar/dissimilar simple variations in sequences (SNPs) are across these groups.

What these studies reveal is something that anyone (myself included) may have intuited just by growing up in various parts of India. There is an amazing breadth of established groups/communities. I mean, anyone who has seen Indian currency will know that we have 15 national languages, and it is quite commonplace to cross state lines and have absolutely no idea what the hell is being spoken (upon which broken English and furious gesticulation will work). But what this study says is that there are basically "Ancestral North Indians" (ANI) and "Ancestral South Indians" (ASI) who have two distinct lineages (Indo-European and Dravidian, respectively), and current day Indians are basically a melange of these two lineages, with ANIs strong in the North and fading towards the South, and vice-versa with ASIs (the other language groups - Austro-asiatic, Tibeto-burman, and Andamanese are sub-variants of ANI and ASIs). This spectrum is reflected in skin color (light to dark), languages, and even caste structure. (Upper and middle tend to be more ANIs, lower castes tend to cluster with ASIs.

The group also makes a case for "founder effects" (basically, genetic bottlenecks) well AFTER 3000 BC when the Dravidians showed up, and 1500 BC when the Indo-European speakers showed up, suggesting that many dispersed communities were established and then they stayed put. The paper also reveals little nuggets - the Santhal and Kharia tribes, which are Austro-asiatic, are descendants of people that arrived 60,000 years ago? Yep, sixTY thousand. The groups also makes the case for marriages within communities (endogamy) has been happening for many centuries, resulting in some interesting disease predispositions.

Overall, this is one really cool study, which you should read (even if the stats may be somewhat inaccessible). As Chakravarti points out, this is only the start - many more detailed analyses should be done on the Indian population to get a true picture of the genetic tapestry that is India.

But that being said, the concept of ANIs and ASIs brings me back to something I have always said : North and South India are two different countries, man...