Dictionary of Human Evolution and Biology

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Fluctuating Asymmetry

Random deviations from perfect symmetry. In operation, measured in two ways:

1. within a population as intra-individual differences between bilateral traits in symmetrical organisms (left side minus right side: e.g. foot width, ankle and hand width, ear length and width, dental dimensions); there has been considerable speculation that individual asymmetries of this type are due to developmental instability and/or stress.

2. proportion within a population displaying a reversal of normal symmetry, e.g. situs inversus viscerum.

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