Symmetry Part 2: Homo Sapiens: The Asymmetric Ape?
Homo Sapiens – humans – by one measure at least – are the most asymmetric of all the great apes. Frederick and Gallup (2007), using previously published data, compared fluctuating asymmetry in the teeth of humans with that of great apes and a number of fossil hominins. Humans showed more dental fluctuating asymmetries than orangutans, gorillas, and chimpanzees. No significant differences between homo sapiens and fossil hominins were found.
Humans may experience less selection pressure from environmental influences when compared to the other great apes. The idea here is that weaknesses resulting from developmental instabilities are less problematic for humans. This implication assumes a close relationship between FA and developmental instability: an assumption which has yet to be established.
The human preference for less FA may have minimal impact on human sexual selection. That is, our attraction to symmetry has not kept us from being what appears to be the least symmetric ape.
Due to the nature of the data, there were no controls for measurement error.
Differences in levels of FA may exist between homo sapiens and at least some extinct hominins – conclusions cannot be drawn from this study.
It is unclear to what degree facial/other asymmetry can be predicted by dental asymmetries – additional comparative studies are in order.
Of potential interest: Orangutans were significantly more symmetric than any of the other great apes. Two explanatory hypotheses were offered:
- Canopy dwelling orangutans may have greater selection pressures for balance – which may be improved with bilateral symmetry.
- Orangutans are the most solitary of the apes – pathogen virulence is negatively correlated with host contact.
Photo courtesy of Tom Low, Camp Leakey, 2003
Michael J. Frederick, & Gordon G. Gallup, Jr. (2007). Fluctuating Dental Asymmetry in Great Apes, Fossil Hominins, and Modern Humans: Implications for Changing Stressors during Human Evolution Acta Psychologica Sinica, 39 (3), 489-494