There are 3 articles in the last issues of "Evolution and Human Behavior" about "fluctuating asymmetry." The data show that laterally challenged people have fewer extra marital partners (a.k.a. "extrapair copulation," wonderful language this field that I love!), have fewer liaisons with those fewer partners, give their partners fewer orgasms, and are judged homelier than is true for the symmetrically blessed. (There's some data that larger people are more symmetrical and, if true, then the added persuasions of being a "supernormal stimulus" are added to those of a balanced image and may confound the entire analysis.) I can't argue with the attraction data. Composite photos average to a symmetrical image that is almost always judged more attractive than the individual pictures. Even women's breasts, if symmetrical, are ranked as a sign of "phenotypic superiority." And larger breasts, per EHB, are likely to be more symmetrical.
The gifts of symmetry are attributed to:
1) Pathogens that interfere with laterality. (One of my tall colleagues remarks loftily, "There is no gene for asymmetry,") 2) The absence of pathogens is presumed to contribute also to greater height, 3) Heterozygosity such that no recessives can impair normal growth, 4) Other developmental stress (N.O.S., not otherwise specified?).
This is pretty bad. I'm thin and barely average height. I had a lot of trouble with sniffles and flu when growing. I also sat at the table a lot rather than finish my dinner (usually sweeping my peas under a chop bone). I'm also cursed with a pointed jaw and small eyes. My blessing is my immense dome, a power symbol equal to the Z for women who really know what's going on. Anyhow, what to do with all this symmetry stuff?
First, kin recognition is a pretty important adaptation. It tells us where to target our altruism and whom not to seduce if we have normal chips for incest avoidance. (A lot of us don't, but that's another story.) Asymmetry should help with kin recognition. And, I wager that similar asymmetric patterns can be observed in several generations in the same family. Suggesting that they have the same pathogen? Or they all experienced the same developmental stresses but 25 years apart?
Second, my symmetric friend, or rather my large friend (I'm not convinced he's symmetrical since he often cocks his head to one side) likely has the same asymmetric brain that I do. If there are no genes for asymmetry, how the H did language, math, music, prosody, and mood regulation take up sides in different halves of the brain? There are people whose minds didn't sort in the customary right/left pattern; however, these same people often have to solve cognitive tasks in a different manner than us lateralists. Given the asymmetric split in Executive Functions (for planning, language internalization, emotional regulation, sequence analysis, and creative synthesis), I'm proud to be so uneven.
Third, could differential patterns of neural output from our asymmetric brains account for laterality in facial expression? Could a drooping eyelid or a right-sided smile tell us something about cerebral activity? My right eyebrow lifts quickly and often; is there something different occurring in my left cortex? Or in my right cortex (for emotionality?) but expressed via transcallosal ties to the left motor areas?
Fourth, the really nasty possibility is that people with even body parts lie more about their other exploits. Larger, symmetrical children are likely treasured more by their parents and experience fewer consequences for lying about themselves. (1)
So much for orgasms even if they do promote sperm retention. Are orgasms lateral? Do asymmetric people have symmetric orgasms? I bet symmetrical people have asymmetrical orgasms. Enough. (2)
1) Forgive me please. I'm still in withdrawal from the Cape seminar on Clinical Sociobiology.
2) See (1).