Two of a Kind: Implications of Bilateral Directional Asymmetry on Pair Matching of Human Limb Bones.

The task of sorting and analyzing commingled remains can be daunting, depending on the degree of fragmentation, distribution, and contents of the assemblage. The Most Likely Number of Individuals (MLNI) calculation for quantifying the contents of human skeletal assemblages is dependent upon the ability to properly match bilateral elements into pairs. Anthropologists employ numerous methods to reassociate commingled remains into discrete individuals, but the guiding principle used to match sided elements is “general symmetry” (Adams and Konigsberg, 2008; Byrd, 2008). However, different skeletal elements and regions within those elements are variably responsive to a combination of environmental and genetic factors. The degree to which certain skeletal regions are susceptible to these factors corresponds to the amount of asymmetry that is likely to be seen within them. For instance, diaphyseal shaft dimensions, which are strongly influenced by mechanical loading, exhibit more asymmetry than the more genetically-constrained regions, articular surfaces and lengths (Auerbach and Ruff, 2006). Skeletal asymmetry has been widely studied in prehistoric and preindustrial populations, but remains minimally explored within modern populations.

This study uses bilateral measurements from a modern sample of adult white males to test which long bone dimensions display the greatest directional asymmetry. Dimensions and skeletal regions that are more resistant to environmental influences, and therefore asymmetry, should be given preference when attempting to match elements. Results support earlier literature documenting the marked directional asymmetry within diaphyseal shaft dimensions, as well as limited plasticity within articular and peri-articular surface and length dimensions.