Fluctuating asymmetry is one way in which an organism can deviate from bilateral symmetry, others being anti-symmetry and directional asymmetry. Fluctuating asymmetry is defined as a random asymmetry about a zero mean value, usually of a low magnitude. It can be measured in the body—as in bilateral symmetry of finger lengths—or in a particular organ. It is related to concepts of symmetry such as facial symmetry, and is believed to measure the ability of the genome to successfully canalize and buffer development to achieve a normal phenotype under imperfect environmental conditions, as implied by Waddington's notion of canalization. As such it is a key concept in evolution and development, and underlies concepts such as resilience or developmental stability—the ability to maintain a normal developmental course under stress.
In individual differences research, FA has been found to have a negative correlation to measurements of human traits such as social dominance, working memory, and intelligence. In old age, facial symmetry has been associated with better cognitive aging. Symmetry also affects physical attractiveness.
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