User:Nd2242/sandbox

Relationship to Personality Factors
Research into Fluctuating Asymmetry suggests that there may be some correlation to specific personality factors, in particular, the Big Five personality traits. From a general view, one would expect someone who is more symmetrical (usually meaning greater attractiveness), to be high on agreeableness, conscientiousness, extraversion and openness, and low on neuroticism. One of the most consistent findings reported is that low Fluctuating Asymmetry is positively associated with measures of extraversion, suggesting that more symmetrical people tend to be more extraverted than less symmetrical people, particularly when specifying to symmetry within the face. However, research is proving less consistent with other personality factors, with some finding some weak correlations between low Fluctuating Asymmetry and conscientiousness and openness to experience, and others finding no significant differences between those with high or low Fluctuating Asymmetry.

Lead
Fluctuating Asymmetry (FA) is the small, random deviations away from perfect bilateral symmetry. As deviations away from perfection, it is thought to reflect the genetic and environmental pressures placed on an individual throughout the developmental process, with greater pressures resulting in higher levels of FA (less symmetrical)..

Measuring FA
Fluctuating asymmetry (FA) can be measured by the equation: Mean FA = mean absolute value of left sides - mean absolute value of right sides.

The closer the mean value is to zero, the lower the levels of FA, indicating more symmetrical features. By taking many measurements of multiple traits per individual, this increases the accuracy in determining that individual's developmental stability. However, these traits must be chosen carefully, as different traits are affected by different selection pressures.[7]

This equation can further be used to study the distribution of asymmetries at population levels, to distinguish between traits that show FA, directional asymmetry, and anti-symmetry.[8][9] The distribution of FA around a mean point of zero suggests that FA is not an adaptive trait, where symmetry is ideal. Directional asymmetry of traits can be distinguished by showing significantly biased measurements towards traits being larger on either the left or right sides, for example, human testicles (where the right is more commonly larger), or handedness (85% are right handed, 15% are left handed). Anti-symmetry can be distinguished by the bimodal distributions, due to some adaptive functions.

Developmental Stability
Developmental stability is achieved when an organism is able to withstand genetic and environmental stress, to display the bilaterally symmetrical traits determined by its developmentally programmed phenotype.[1][24] To measure an individual's developmental stability, the FA measurements of 10 traits are added together, including ear width, elbows, ankles, wrists, feet, length of ears and fingers. This is achieved by: (L - R)trait 1 + (L - R)trait 2 + ......(L - R)trait 10. This provides a good overall measure of body FA, as every individual has some features that are not perfectly symmetrical.

Common environmental pressures leading to lower developmental stability include exposure to toxins, poison and infectious diseases, low food quality and malnutrition. Genetic pressures include spontaneous new mutations, and "bad genes" (genes that once had adaptive functions, but are being removed through evolutionary selection). A large fluctuating asymmetry (FA) and a low developmental stability suggests that an organism is unable to develop according to the ideal state of bilateral symmetry. The energy required for bilateral symmetry development is extremely high, making perfect bilateral symmetry rare. Energy is invested into survival in spite of the genetic and environmental pressures, before making bilaterally symmetrical traits. Research has also revealed links between FA and depression, genetic or environmental stress and measures of mate quality for sexual selection.[25][26][27][28]

Non-human animals.
Many non-human animals have been shown to be able to distinguish between potential partners, based upon levels of FA. As with humans, lower levels of FA are seen in the most reproductively successful members of the species. For instance, FA of male forewing length seem to have an important role in successful mating for many insect species, such as dark-wing damselflies and Japanese scorpionflies. In the dark-winged damselfly (Calopteryx maculate), successfully mating male flies showed significantly lower levels of FA in their forewings than unsuccessful males, while for Japanese scorpionflies, FA levels are a good predictor for the outcome of fights between males in that more symmetrical males won significantly more fights. Other animals also show similar patterns, for example, many species of butterfly, males with lower levels of FA tended to live longer and flew more actively, allowing them to have more reproductive success. Also, female swallows have been shown to prefer longer, and more symmetrical tails as a cue for mate choice. Therefore, the males with longer and more symmetrical tails show higher levels of reproductive success with more attractive females. In red deer, sexual selection has effected antler development, in that larger and more symmetrical are favoured in males at prime mating age.

However, some evidence for the effects of sexual selection of FA levels have been inconsistent, suggesting that the relationship between FA and sexual selection may be more complex than originally thought. For instance, in the lekking black grouse and red junglefowl, no correlations were found between FA and mating success. Furthermore, paradise whydahs' tails were experimentally manipulated to be more and less symmetrical, where females showed no preferences for more symmetrical tails (but they did show preferences for longer tails).