When right differs from left: Human limb directional asymmetry emerges during very early development

Abstract

The often observed directional asymmetry (DA) in human limb bones may have a genetic/developmental basis and/or could emerge from different mechanical loadings across sides due to handedness. Because behavioural lateralization in itself has a genetic basis, it has been suggested that DA in limbs could develop prenatally as a pre-adaptation to adult life. However, the presence of consistent differences in the size of left and right limb bones in early development is understudied. We study asymmetry in limb bones during early development (10–20 weeks of gestation) in a sample of 178 aborted foetuses. Statistically significant DA was found in several upper and lower limb bones, where the right-hand side was consistently larger than the left. We argue that this pattern is probably the consequence of developmental processes related to internal asymmetric positioning of organs.

Keywords:

• Fluctuating asymmetry
• Directional asymmetry
• Human
• Foetus
• Handedness

Additional information

Funding

Funding: This research was financially supported by Grant for a Short Scientific Mission for the COST 23B Action (Oral Facial Development and Regeneration) of the European Science Foundation to FG and by the Fund for Scientific Research (FWO)—Flanders (postdoctoral grant to JB and research programme G.0027.07 to SVD). Ethical approval (approval number 648/32/300/05) to study the human collection of embryos and foetuses owned by the University of Turku was obtained from the National Supervisory Authority for Welfare and Health of Finland (VALVIRA).