Monday , 24 September 2018

Tribute To “Luca” Cavalli-Sforza

Nandkumar Kamat

What Newton is to Newtonian Physics, Einstein to theory of relativity, Darwin to theory of natural selection, Edward O. Wilson to biodiversity studies, Luigi Luca Cavalli-Sforza, Italian population geneticist is to study of molecular geography and anthropology of genes. Among generations of population geneticists he was fondly called as “Luca”. He died in Belluno, Italy on August 31 at the age of 96.

An article in Scientific American “Genes, people and languages” which I read in 90s made me his fan and subsequently I purchased all the important books he had authored. Photo Journalist and heritage activist Vivek Menezes and NRI Goan Physician Santosh Helekar also gifted me two of his popular books. Sforza would be remembered for his magnum opus ‘The Great Human Diasporas: The History Of Diversity and Evolution’ written with his son as co-author. Born in Genoa, Italy, on January 25, 1922, Cavalli-Sforza was trained as a physician from the University of Pavia in 1944. He began his career as a microbiologist after joining geneticist Ronald Fisher at the University of Cambridge and took interest in bacterial genetic variation and statistics.

His subsequent work reveals a fine mathematical and computational mind. He taught in Italian Universities between 1951 and 1970 and made a name for himself as a teacher, geneticist and thinker. His genius and original mind was noticed by Stanford University in 1970. They made him a Professor, a position on which he continued till 1992. At Stanford University he began collaborating with evolutionary biologist Marcus Feldman. This intellectual and research partnership lasted for four decades and saw some of great work in areas of human population genetics and its molecular basis being published. Cavalli-Sforza and Feldman developed the gene-culture evolutionary theory. According to this theory we can understand the behaviour of humans as the result of the interplay between genetic and cultural evolution. Cavalli-Sforza then undertook from Paris an ambitious project to catalogue the cell lines of human populations across the world. His Human Genome Diversity Project focused on genetic variations in human populations. In his tribute paleoanthropologist John Hawks has beautifully summarized his major contributions to establish a linkage between human migrations and evolution of genes and languages.

Hawks wrote recently: “During the 1980s, Cavalli-Sforza worked to synthesize the growing evidence base of human genetic variation around the world. He side-stepped the brouhaha over mitochondrial Eve, pointing out that while the new DNA sequence-based approaches could trace the history of a single gene with great accuracy, they were not yet capable of combining information from many genes. He went to work building trees that could summarize the relationships of entire populations, not just individuals. In doing so, he struck upon a collaboration with a group of maverick linguists, who believed they could build a universal tree of human languages. The intellectual leader of these linguists was Joseph Greenberg. Greenberg eschewed the approach followed by most historical linguists to reconstruct language relationships. Where most other specialists tried to reconstruct a full history of sound changes and shared grammatical constructs, Greenberg instead took the much simpler approach of comparing common words. In his view, this approach would enable recognition of much deeper, more ancient relationships among languages — most controversially, he suggested that all Native American languages could be grouped into three large families instead of the dozens recognized by other linguists.”

This work called Anthropological genetics later influenced Indian researchers as well and during past 20 years we saw an explosion of research papers in India shedding light on human migrations in Indian subcontinent and south Asia and the interrelationship between different languages of the Indian subcontinent. To illustrate, Pitchappan, R M, and G Arunkumar in their paper Evolution and Implications of Genomic Diversity on “Human Kind” in India published in the book – On Human Nature in 2017 reported – “India, the second continent successfully occupied by Homo Sapiens, is known for its enormous diversities as outcome of early migrations, autochthonous expansion and cultural evolution. The first coastal out-of-Africa migration ∼60,000 ybp allowed humans to leave their trails of non recombinant Y chromosome (NRY) haplogroup (HG) signatures in the Western Ghats and various parts of India, which gave rise to further autochthonous evolution of the male gene pool.

Monsoons transformed the early settlers into hill tribes and dry land farmers, leading to sedentary lives. Subsequently, migration of the Neolithic cattle keepers and people with water-taming technology (characterised by NRY HGs J and R lineages, respectively) ushered in domestication along with river-fed and wet-land cultivation. The success of the resultant geographic demes was further augmented by the advent of languages. Language families correlated with one or the other NRY clade, namely, Dravidian languages correlated to NRYHG L1 dating to 30,000 ybp; Austroasiatic languages spoken in East India with O2a dating to 20,000 ybp; and Indo-European spoken in North India with R1a dating to 15,000 ybp. Cultural evolution, such as societal formation, religious ethos, etc further crystallised this diversity in the recent past. Studies on the whole genome—NRY, mtDNA, major histocompatibility complex (MHC), and non-MHC genes—have supported this contention of migration, settlement, expansion, and sympatric isolation in India. “Hundreds of such research papers are indirect tributes to the work initiated by Cavalli-Sforza. World misses Luca.

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