What our DNA foretells

The book is brilliantly lucid in its explanations of methodology, and specific studies. It's written from a standpoint of humility.

Who We Are and How We Got Here

Ancient DNA and the New Science of the Human Past

David Reich

OUP

368 pages; Rs 495

Let’s start with the non-controversial elements. The author is a geneticist, who specialises in the study of ancient DNA. His Harvard lab isolated Neanderthal genes and figured out ratios of Neanderthal genes in modern human genomes.

Mr Reich uses highly sophisticated techniques to extract DNA from bones and works out genome-wide characteristics of ancient populations. Statistical methods can then be used to make educated guesses at human migration patterns, by comparing ancient DNA data to modern DNA. Those can be tied to written history, oral myths, and so on.  

Archaeology, anthropology and linguistics are the disciplines traditionally used to delve into “deep history” —  the distant past. By 2010 or so, DNA technology could not only supplement these; it often improved by providing rigorous, data-backed answers to unanswered questions.

This is, in itself, explosively controversial. The data indicates human populations have been mixing since the time of the Neanderthals. Ancient DNA studies also provide data about other ticklish issues like racial propensity to disease, plus genomic and gender inequalities. Geneticists can be culturally ignorant, and bigoted, so there can be missteps as well. Thus, Mr Reich describes ancient DNA geneticists as “barbarians with new tools who cannot be ignored”.

The science is fascinating. It’s possible to distinguish between genes inherited from the mother (by looking at mitochondria) and the father (studying the Y-chromosome). Geneticists can make strong guesses as to when two groups intermarried, by studying DNA sequence length in chromosomes.

Most of the tech breakthroughs happened in the last decade, including methods to extract and isolate genome-wide DNA from skeletons in hot climates. The speed of analysis has increased, and the costs have dropped exponentially. The availability of multiple databases with millions of DNA profiles has also made it easier to do broad comparative studies.

The book is brilliantly lucid in its explanations of methodology, and specific studies. It's backed by good footnotes. It's written from a standpoint of humility. Mr Reich believes many cutting-edge methods will soon be outdated and expects much higher levels of specialisation.  

On a personal note, he’s an Ashkenazi (European) Jew with orthodox relatives. His Mama is a rabbi, who debated with him about the moral dilemma of his desecrating graves for the sake of knowledge. His family fled Europe in the 1930s as a direct result of murderous, racial theories.  So, he has a good understanding of bigotry, of endogamy (marrying only within the community) and arranged marriage (which is common enough among Ashkenazis). Indeed, he says Ashkenazis are a “caste” from a non-casteist society (Europe).  

The book describes current ancient DNA conclusions about population migrations across the world. I'm focussing on Chapter 6, “The Collision that formed India,” for obvious reasons. Mr Reich and his team worked with Lalji Singh and Kumarasamy Thangaraj at the Centre for Cellular and Molecular Biology (CCMB) Hyderabad.  They looked at modern DNA samples drawn from various Indian communities and he also quotes multiple other studies.

Here are some conclusions. Ancient India had two major highly differentiated groups, an Ancestral South Indian (ASI) and an Ancestral North Indian (ANI). Those two groups started inter-marrying about 4,000 years ago. Every modern Indian outside of the Little Andaman tribe has a mix of ANI and ASI genes. The Little Andaman tribe was used as a control since it is unmixed ASI. ASI genes are more predominant in Dravidian speakers. Speakers of Sanskrit-based languages have higher ANI ratios. 

The ANI genome contains genes characteristic of West Eurasians. Both ASI and ANI genomes contain genes characteristic of Iranian farmers. The best fit for these data: many waves of migrations into the subcontinent. Ongoing DNA studies of skeletons at the Rakhigarhi Harappan site (which dates back 5,000 years) may yield more information.

Reich & Co discovered some other things. The vast majority of ANI genes were transmitted down the male side. This implies ANI males had the social power to propagate by impregnating ASI women. Similar ratios are seen of high male propagations of North European genes in African American and Native American populations.  

Indian endogamy has existed for millennia. “Population bottlenecks” occur for endogamic communities with a high reproductive rate. This results in rare, isolated mutations due to recessive genes.  The Ashkenazi are a bottlenecked population.

There are a massive number of bottleneck groups in India. Mr Reich says India consists of “a large number of small populations”. The research implications are huge: If a group with very specific genes is prone to certain diseases, it is much easier to isolate the responsible genes. He cites one known condition — the sensitivity of vyasas from Andhra Pradesh to muscle relaxants — and wishes there was an India-wide study of such genetic factors. This could lead to insights that positively impact hundreds of millions.

There's a lot more to the book than this, including thoughts on how genetic studies could change views of “race”.  It’s very well-written but guaranteed to be controversial — indeed, it has already evinced hysterical reactions in global social media, and academia too.  Please read with an open mind.