# David Reich (geneticist)

David Emil Reich (born July 14, 1974) is an American geneticist known for his research into the population genetics of ancient humans, including their migrations and the mixing of populations, discovered by analysis of genome-wide patterns of mutations. He is professor in the department of genetics at the Harvard Medical School, and an associate of the Broad Institute. Reich was highlighted as one of Nature's 10 for his contributions to science in 2015. He received the Dan David Prize in 2017, the NAS Award in Molecular Biology, the Wiley Prize, and the Darwin–Wallace Medal in 2019. In 2021 he was awarded the Massry Prize.

## Early life and education

Reich grew up as part of a Jewish family in Washington, D.C. His parents are novelist Tova Reich (sister of Rabbi Avi Weiss) and Walter Reich, a professor at George Washington University, who served as the first director of the United States Holocaust Memorial Museum. David Reich started out as a sociology major as an undergraduate at Harvard College, but later turned his attention to physics and medicine and earned a B.A. in the subject. After graduation, he attended the University of Oxford, originally with the intent of preparing for medical school. He was awarded a D.Phil. in zoology from St Catherine's College, Oxford, in 1999 for research supervised by David Goldstein. His thesis was titled "Genetic analysis of human evolutionary history with implications for gene mapping".

## Academic career

He joined Harvard Medical School in 2003. Reich is currently a geneticist and professor in the department of genetics at Harvard Medical School, and an associate of the Broad Institute, whose research studies compare the modern human genome with those of chimpanzees, Neanderthals, and Denisovans.
Reich's genetics research focuses primarily on finding complex genetic patterns that cause susceptibility to common diseases among large populations, rather than looking for specific genetic markers associated with relatively rare illnesses.

## Genetic research
### Split of chimpanzees and humans (2006)

Reich's research team at Harvard University has produced evidence that, over a span of at least four million years, various parts of the human genome diverged gradually from those of chimpanzees. The split between the human and chimpanzee lineages may have occurred millions of years later than fossilized bones suggest, and the break may not have been as clean as previously thought. The genetic evidence developed by Reich's team suggests that after the two species initially separated, they may have continued interbreeding for several million years. A final genetic split transpired between 6.3 million and 5.4 million years ago.

### Indian population (2009)

Reich's 2009 paper Reconstructing Indian population history was a landmark study in the research on India's genepool and the origins of its population. Reich et al. (2009), in a collaborative effort between the Harvard Medical School and the Indian Centre for Cellular and Molecular Biology (CCMB), examined the entire genomes worth 560,000 single-nucleotide polymorphisms (SNPs), as compared to 420 SNPs in prior work. They also cross-compared them with the genomes of other regions available in the global genome database. Through this study, they were able to discern two genetic groups in the majority of populations in India, which they called "Ancestral North Indians" (ANI) and "Ancestral South Indians" (ASI). They found that the ANI genes are close to those of Middle Easterners, Central Asians and Europeans whereas the ASI genes are dissimilar to all other known populations outside India. These two distinct groups, which had split ca. 50,000 years ago, formed the basis for the present population of India.
A follow-up study by Moorjani et al. (2013) revealed that the two groups mixed between 1,900 and 4,200 years ago (2200 BCE–100 CE), after which a shift to endogamy took place and admixture became rare. Speaking to Fountain Ink, David Reich stated, "Prior to 4,200 years ago, there were unmixed groups in India. Sometime between 1,900 to 4,200 years ago, profound, pervasive convulsive mixture occurred, affecting every Indo-European and Dravidian group in India without exception." Reich pointed out that their work does not show that a substantial migration occurred during this time.
Metspalu et al. (2011), representing a collaboration between the Estonian Biocenter and CCMB, confirmed that the Indian populations are characterized by two major ancestry components. One of them is spread at comparable frequency and haplotype diversity in populations of South and West Asia and the Caucasus. The second component is more restricted to South Asia and accounts for more than 50% of the ancestry in Indian populations. Haplotype diversity associated with these South Asian ancestry components is significantly higher than that of the components dominating the West Eurasian ancestry palette.

### Human genetic map (2011)

Reich was a co-leader, along with statistician Simon Myers, of a team of genetics researchers from Harvard University and the University of Oxford that made the most complete human genetic map then known in July 2011.

### Interbreeding of Neanderthals and humans (2010–2012)

Reich's research team significantly contributed to the discovery that Neanderthals and Denisovans interbred with modern human populations as they dispersed from Africa into Eurasia 70,000–30,000 years ago.

### Genetic markers for prostate cancer

Reich's lab received media attention following its discovery of a genetic marker which is linked to an increased likelihood of developing prostate cancer. Reich has also argued that the higher incidence of prostate cancer among African Americans, compared to European Americans, appears to be largely genetic in origin.

### Indo-European origins

Reich has suggested that the Indo-European languages may have originated south of the Caucasus, in present-day Iran or Armenia:
   "Ancient DNA available from this time in Anatolia shows no evidence of steppe ancestry similar to that in the Yamnaya (although the evidence here is circumstantial as no ancient DNA from the Hittites themselves has yet been published). This suggests to me that the most likely location of the population that first spoke an Indo-European language was south of the Caucasus Mountains, perhaps in present-day Iran or Armenia, because ancient DNA from people who lived there matches what we would expect for a source population both for the Yamnaya and for ancient Anatolians. If this scenario is right the population sent one branch up into the steppe – mixing with steppe hunter-gatherers in a one-to-one ratio to become the Yamnaya as described earlier – and another to Anatolia to found the ancestors of people there who spoke languages such as Hittite."

### Eurasian back-migrations

Reich in 2018 demonstrated based on genetic evidence, West Asian geneflow into modern Afro-Asiatic speaking African populations could support a diffusion of these languages from the Middle East:
   "New insights are already emerging from ancient DNA, which makes it possible to document ancient migrations between the Near East and North Africa that could have spread languages, culture, and crops. In 2016 and 2017, my laboratory published two papers showing that a shared feature of many East African groups, including ones that do not speak Afroasiatic languages, is that they harbor substantial ancestry from people related to farmers who lived in the Near East around ten thousand years ago. Our work also found strong evidence for a second wave of West Eurasian-related admixture this time with a contribution from Iranian-related farmers as might be expected from a spread from the Near East in the Bronze Age-and showed that this ancestry is widespread in present-day people from Somalia and Ethiopia who speak Afroasiatic languages in the Cushitic sub-family. So the genetic data provide evidence for at least two major waves of north-to-south population movement in the period when Afroasiatic languages were spreading and diversifying, and no evidence of south-to-north migration."

### Software tools

Reich has developed ADMIXTOOLS 2, an R software package primarily used for analyzing admixture, in collaboration with Nick Patterson.

## Books

* Who We Are and How We Got Here, Oxford University Press, 2018