Fluctuating asymmetry

Fluctuating asymmetry is an organism’s deviation from bilateral symmetry. 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 associated with human traits such as social dominance, working memory, and intelligence. In old age, facial symmetry has been associated with better cognitive aging. There is some evidence that the degree of bodily symmetry in individuals influences our assessment of how well they dance, supporting Darwin's suggestion that dance is a sexually selected courtship signal.

Symmetry also affects physical attractiveness.