Unicausal theories of human canine evolution: are they sufficient?

Most theories of human canine evolution are unicausal and only purport to explain size and related shape changes in human canines. The present work tests whether one of the morphological changes, dulling of the distal edge of the maxillary canine, can be entirely explained as a byproduct of changes in the overall shape of the canine. The data show that the distal edge of maxillary canines of A. afarensis became far duller than would be predicted from changes in crown shape. The greater than expected dullness of the distal edge can be explained by evolutionary changes in the genetic field for cheek tooth morphology. This suggests that human canine evolution is complex and cannot be accounted for by unicausal theories.