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Limb bone bilateral asymmetry: variability and commonality among modern humans

Summary: Limb bone bilateral asymmetry: variability and commonality
among modern humans
Benjamin M. Auerbach*, Christopher B. Ruff
Center for Functional Anatomy & Evolution, The Johns Hopkins University School of Medicine, 1830 East Monument Street,
Baltimore, MD 21205, USA
Received 19 May 2005; accepted 30 September 2005
Humans demonstrate species-wide bilateral asymmetry in long bone dimensions. Previous studies have documented greater right-biases in
upper limb bone dimensionsdespecially in length and diaphyseal breadthdas well as more asymmetry in the upper limb when compared with
the lower limb. Some studies have reported left-bias in lower limb bone dimensions, which, combined with the contralateral asymmetry in upper
limbs, has been termed ``crossed symmetry.'' The examination of sexual dimorphism and population variation in asymmetry has been limited.
This study re-examines these topics in a large, geographically and temporally diverse sample of 780 Holocene adult humans. Fourteen
bilateral measures were taken, including maximum lengths, articular and peri-articular breadths, and diaphyseal breadths of the femur, tibia,
humerus, and radius. Dimensions were converted into percentage directional (%DA) and absolute (%AA) asymmetries. Results reveal that av-
erage diaphyseal breadths in both the upper and lower limbs have the greatest absolute and directional asymmetry among all populations, with
lower asymmetry evident in maximum lengths or articular dimensions. Upper limb bones demonstrate a systematic right-bias in all dimensions,
while lower limb elements have biases closer to zero %DA, but with slight left-bias in diaphyseal breadths and femoral length. Crossed sym-
metry exists within individuals between similar dimensions of the upper and lower limbs. Females have more asymmetric and right-biased upper
limb maximum lengths, while males have greater humeral diaphyseal and head breadth %DAs. The lower limb demonstrates little sexual di-
morphism in asymmetry. Industrial groups exhibit relatively less asymmetry than pre-industrial humans and less dimorphism in asymmetry.


Source: Auerbach, Benjamin M. - Department of Anthropology, University of Tennessee


Collections: Biology and Medicine