a | Map of the world illustrating the geographical boundaries that historically have been used to classify populations into the different racial groups: Africans (blue), Europeans (green), Asians (red) and Native Americans (brown)⁷⁸. Africa and Asia are the continents of origin of more than one racial group, and the boundaries between racial groups are not discrete. The geographical origin of each local population from the CEPH HUMAN DIVERSITY PANEL is numbered, and the populations are classified according to the definition of the US Office of Management and Budget (see online supplementary information S4 (data)). b | Matrix of probabilities of randomly choosing two individuals from different 'racial' populations (see text for details) who are more dissimilar, based on the number of shared short tandem repeat (STR) alleles, than two randomly chosen individuals from the same population. For example, an African will be more dissimilar to an Asian individual compared with another African individual ∼65% of the time. c | Distribution of the mean number of pairwise differences of STRs per locus of individuals within (black line) and between (red line) populations summed across Africans, Asians, Europeans and Native Americans. There is substantial overlap between the distributions, but the mean number of repeats per locus between individuals from different populations is frequently greater than between individual from the same population.