The 82nd Annual Meeting of the American Association of Physical Anthropologists (2013)

Bilateral asymmetry of humeral torsion and length in African apes and humans


Department of Anthropology, University College London

Saturday 1:00-1:15, Ballroom C Add to calendar

While forelimb asymmetries have been well documented in the human skeleton, few studies have documented such asymmetries in the African apes, even though these are potentially informative about the origins of functional lateralization in humans and non-human primates. We report the magnitude (absolute asymmetry) and direction (directional asymmetry) of asymmetries in humeral torsion and humeral length in paired humeri of 40 Gorilla gorilla, 40 Pan troglodytes and 40 Homo sapiens. Here, we test whether absolute (%AA) and directional (%DA) asymmetries differ between measurements, between species and between sexes. Our results show that: (1) humans are unique in being strongly right-lateralized for both measurements, which is consistent with handedness patterns; (2) humans are also more asymmetric than apes in length, suggesting the presence of pressures favoring the maintenance of limbs of similar lengths in apes and/or larger more dominant right arms in humans; (3) contrary to expectation, torsion asymmetries in apes occur in the same magnitude as in humans, suggesting that individual preferences are responsible for functional lateralization in apes, whereas in humans this is a population-level pattern; (4) sex differences in torsion directionality are observed in gorillas, but not chimpanzees, consistent with behavioral differences linked to body size dimorphism in this species, and sex differences in length asymmetry are found in humans, consistent with previous studies; finally, (5) torsion asymmetries are more pronounced than length asymmetries in all samples, consistent with higher levels of plasticity in humeral torsion in response to biomechanical stimuli and greater genetic canalization of lengths.

Funded by Fundação para a Ciência e a Tecnologia [SFRH/BD/60349/2009]

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