An overall reduction in tooth size was recognized some 80 years ago as a feature of human evolution. Various explanations have been offered – including dietary change and the acquisition of cooking – but the underlying developmental basis for this trend remained unknown. Alistair Evans et al. examined tooth size in fossil hominins and great apes in a sample spanning the last seven million years and find that the inhibitory cascade, an activator–inhibitor mechanism that affects relative tooth size in mammals, produces the default pattern of primary postcanine tooth sizes for all lower primary postcanine teeth. Using this model, the authors demonstrate a tight link between tooth proportions and absolute size in hominins, such that the size at one tooth position can predict the sizes of the remaining four primary postcanine teeth in the row.
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