Luigi Luca Cavalli-Sforza. 25 January 1922—31 August 2018

Though it was as a bacteriologist that Luca Cavalli-Sforza first flourished scientifically, it was the subject of human population genetics that he dominated for the second half of the twentieth century. He pioneered both genetical demography and the construction of the genetical evolutionary tree of man, initially from gene-frequency data and ultimately from tracing the paths of descent of individual DNA sequences. He was among the first to apply the new computers to the problems he encountered, using his self-taught knowledge of mathematics and statistics. He conducted expeditions to the Pygmies of the African rainforest and studied the spread of agriculture in Europe, demonstrating the similarity between its wave of advance and the contours of population gene frequency. He noted the correspondence between the descent tree of languages and the human evolutionary tree. Cavalli headed university departments in Pavia and then Stanford, surrounding himself with young colleagues and driving forward research with vigorous discussion and unceasing enthusiasm. His knowledge was spread across medicine and genetics, anthropology and linguistics, archaeology and history, and he expressed himself fluently in speech and writing in Italian, English and French. A true Renaissance man. His published work in human population genetics and cultural evolution over more than 50 years constituted ‘one long argument’, as Darwin said of The origin of species . The villages of the Parma valley were his Galapagos Islands, and random genetic drift his adjunct to natural selection for the case of man. His demonstration of the importance of drift in recent human evolution informed the model for constructing evolutionary trees from gene-frequency data. On this one long argument he wrote and lectured ceaselessly, not only for other scientists but also for a wider audience, always mindful of a responsibility to promote an understanding of man's biology and evolutionary history for society's benefit. In so doing he brought an informed and rational approach to the problem of human diversity and the problems of human diversity.