Mark G. Thomas is Professor of Evolutionary Genetics at the Research Department of Genetics, Evolution and Environment at University College London. In 2009 – in collaboration with Prof Stephen Shennan and Dr Adam Powell – Thomas published a study in the journal Science showing that population density and or migratory activity are likely to be a major determinants in the maintenance or loss of culturally inherited skills, and that this seemed to explain a number of curious features of the appearance of behavioural modernity in humans at different times in different parts of the world.