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.
- Valen, Leigh Van (June 1962). "A Study of Fluctuating Asymmetry". Evolution 16 (2): 125–142. JSTOR 2406192.
- Waddington, Conrad Hal (1957). The Strategy of the Genes. George Allen & Unwin. p. 262.
- Furlow, B; Gangestad, SW, Armijo-Prewitt, T (1998-01-07). "Developmental stability and human violence.". Proceedings of the Royal Society B 265 (1390): 1–6. doi:10.1098/rspb.1998.0255. PMID 9470212.
- Yeo, RA; Hill, D; Campbell, R; Vigil, J; Brooks, WM (2000). "Developmental instability and working memory ability in children: a magnetic resonance spectroscopy investigation.". Developmental neuropsychology 17 (2): 143–59. doi:10.1207/S15326942DN1702_01. PMID 10955200.
- Furlow, FB; Armijo-Prewitt, T; Gangestad, SW; Thornhill, R (1997-06-22). "Fluctuating asymmetry and psychometric intelligence.". Proceedings of the Royal Society B 264 (1383): 823–9. doi:10.1098/rspb.1997.0115. PMID 9265189.
- Bates, T (1 January 2007). "Fluctuating asymmetry and intelligence". Intelligence 35 (1): 41–46. doi:10.1016/j.intell.2006.03.013.
- Prokosch, M; Yeo, R; Miller, G (1 April 2005). "Intelligence tests with higher -loadings show higher correlations with body symmetry: Evidence for a general fitness factor mediated by developmental stability". Intelligence 33 (2): 203–213. doi:10.1016/j.intell.2004.07.007.
- Penke, Lars; Bates, Timothy C.; Gow, Alan J.; Pattie, Alison; Starr, John M.; Jones, Benedict C.; Perrett, David I.; Deary, Ian J. (1 November 2009). "Symmetric faces are a sign of successful cognitive aging". Evolution and Human Behavior 30 (6): 429–437. doi:10.1016/j.evolhumbehav.2009.06.001.
- Wade, T. J. (2010). "The Relationships between Symmetry and Attractiveness and Mating Relevant Decisions and Behavior: A Review". Symmetry 2 (2): 1081. doi:10.3390/sym2021081.