Human Attraction - Symmetry
Humans find symmetry among other humans attractive. This has an evolutionary origin (which is pretty obvious, when you consider damn near all animals find symmetry attractive, and many choose mates based solely on how symmetric they are) which is actually based on fetal development. When a fetus is developing, ideally it should develop to be completely symmetric, however any environmental disturbances can harm fetal development and cause slight (or severe) asymmetric development. Therefore, when someone is very asymmetric, there's also a likelihood that they have slight internal defects as well, which may harm their health and make them a poor mate. Also, this may be an indication that their mother (and possibly their father, in species which raise their young in pairs or groups) was not particularly well adapted to sufficiently avoid deprivation or harm during pregnancy. Since this is likely caused by genetic factors, an asymmetric organism is less likely to produce healthy offspring.
And then, of course, there's always the problem that symmetry is very useful for many species. For example, a fly could not fly as well with two uneven wings as it could if they were identical, which puts it at a competitive disadvantage.
And then, of course, there's always the problem that symmetry is very useful for many species. For example, a fly could not fly as well with two uneven wings as it could if they were identical, which puts it at a competitive disadvantage.