A simple rule that can explain the evolution of tooth size in hominins is reported online in Nature this week. The study enables the prediction of the expected sizes of a row of teeth using a single isolated tooth.
Hominin tooth size has decreased throughout evolution. Although this phenomenon has been attributed to changes in diet or the advent of cooking, the mechanism underlying variation in tooth size has not been well understood.
Alistair Evans and colleagues analysed tooth size in modern humans and fossilized hominins to determine whether a developmental mechanism (the inhibitory cascade model) that controls relative molar size in mice could be applied to hominins and great apes. They find a strong relationship between the absolute and relative sizes of the primary postcanine teeth, which include the ‘baby’ premolars and permanent molars. This pattern of tooth size is constant with absolute tooth size in the australopiths, but the scaling relationship differs in species of Homo on the basis of the size of the first molar. These findings could help to resolve a number of controversies in human evolution.