Toomas Kivisild, University of Tartu, University of Cambridge
Richard Villems, University of Tartu
Sandra Beleza, University of Leicester
In "The Descent of Man", his famous book published more than 140 years ago, the great British naturalist Charles Darwin, devoted much attention to the variation within and across human populations. He convincingly argued that humanity, irrespective of considerable phenotypic and cultural differences, is a single race that shares a common root with greater apes in some distant past. Furthermore, he also pointed out that much of the observed variation can be explained by natural selection and stressed on the potential role of admixture between human communities. Darwin's ideas had a considerable influence both for science and much wider. But only over the last decades, with better approaches available, we are beginning to understand the genetic basis of the phenotypic variation and various human adaptations. The field of population genetics, with its advancements in data acquisition and analysis, is by now a fast-growing active field of scientific enquiry, yet very much still in its initial stages, because causative explanations require synthesis of genetics and genomics, evolutionary reasoning, with in-depth knowledge of human physiology, biochemistry and developmental biology, often linked to social and cultural advancements of our species in a broader sense.
South Asia, bearing in mind geographic, linguistic, socio-cultural and phenotypic diversity of the region, offers a rich in detailed model system to test various evolutionary hypotheses and to reconstruct the events that helped us to shape what we are today. Hence, in the current dissertation, we have broadly covered two general aims related to human diversity. Firstly, to decipher the genetic attributes of two important adaptive traits in humans - skin color and lactase persistence (the unique ability to digest lactose in adulthood) and secondly, to reconstruct the population history of Austroasiatic-speaking populations presently settled in South and Southeast Asia.
Our expedition, involving skin color measurements, reflected high pigmentation diversity among local inhabitants. Our further analyses revealed SLC24A5 as one of the main determinants of skin pigmentation variation among South Asians. Additionally, an evolutionary approach was used to study the gene and important insights on the selection patterns, phylogenetic relationships and diversity patterns among global populations were obtained. We found that light skin associated variant of SLC24A5, shared by West Eurasians and South Asians, occur on the same haplotype background and we suggest its identity by descent. Our study of enhancer region of LCT among Indian populations provided a comprehensive view on the genetic basis of lactase persistence in the subcontinent. Phylogeography of the important candidate SNPs for the studied traits further revealed that combination of processes involving selection and demography have been crucial in the evolution of these traits. An integrated genetic approach of mitochondrial DNA, Y chromosome and autosomes to delineate the ancestry palette of Austroasiatic-speaking populations refined our understanding of their origin and dispersal routes. Autosomal analyses, in particular, provided the first evidence of bidirectional gene flow(s) alongside of the Bay-of-Bengal. We propose that the present-day Austroasiatics, at least in case of Munda, are derived from dispersal from Southeast Asia, followed by admixture with local Indian populations. The conclusions obtained in the dissertation thus bear significance in improving our general understanding of the evolutionary architecture of the studied adaptive traits and unique demographic processes that govern the genetic structuring of the present-day South Asians.