Asterisk The symbol*, used in this book to identify terms with an entry of their own. Often written 'Asterix' by French schoolchildren. Find out why.
Asymmetry The results of differences between the 'sides' of structures with one or more longitudinal axes, such as the body ofan animal. Echin-oderms and coelenterates - CD's *Zoophites -whose bodies are radially symmetrical, have many opportunies for asymmetries (see, for example, Edwards 1966). Some echinoderms, such as the sand dollars and the sea cucumbers, sport variable mixtures of bilateral and radial symmetry, resulting in various asymmetries, depending on one's standpoint. Hence CD's definition of assymetrical as having two sides unlike (Origin VI, p. 431) is incomplete.
The bilaterally symmetrical vertebrates only rarely have genes coding for external asymmetries (although asymmetry ofinternal organs is the rule). Notable exceptions are the *Cichlidae, the *flatfishes, and the *Jenynsiinae, wherein species and/or populations may be defined by the orientation of their asymmetry. Another exception is the *lancelet, whose slight asymmetry may be vestigial (see Dohrn).
Except in these groups, externally visible asymmetries can therefore be used, in the context of *sexual selection, to evaluate whether a potential partner has suffered from develop mental errors, *parasites, predator attacks, or diseases (see Morris etal. 2003;Reimchen 1988, 1992,1997; Sasal and Pampoulie 2000), all of which invariably generate asymmetric injuries. Indeed, many animals, including fishes, generate colour patterns ofintricate symmetry, i.e. in which asymmetries are easily detected. Such a *handicap may help females evaluate the true fitness ofmales.
Laterality is a form of asymmetry reflected in the preferred use, by animals, of (appendages on) their left or right side. It is known as 'hand-edness' in humans.
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