Fluctuating dental asymmetry in great apes, fossil hominins, and modern humans: Implications for changing stressors during human evolution

Abstract

Fluctuating asymmetry (FA), defined by random, stress-induced deviations from perfect bilateral symmetry, is an indication of the inability to buffer against developmental disturbances, such as poor early nutrition. One method of measuring FA involves comparing individual tooth sizes on opposing sides of the mouth. In this study tooth measurements were compiled for 296 individuals from 10 species, including chimpanzees (Pan troglodytes), orangutans (Pongo pygmaeus), gorillas (Gorilla gorilla), modern humans (Homo sapiens), and a number of fossil hominins. The orangutan sample had significantly lower levels of dental FA than the gorilla, chimpanzee, Homo erectus, neandertal, or modern human samples. In contrast, the human and neandertal samples had significantly higher dental FA levels than any of the great ape samples. Some explanations relating to relaxed selection pressures are suggested.