However, the pioneering research of Randy Thornhill, UNM Regents' professor of biology, and Steven Gangestad, professor of psychology, has shown that beauty may not be entirely skin deep. There are a number of biological constants that transcend culture, ethnicity, and advertising campaigns. One of these is bilateral symmetry, which is how well your left side matches your right. Thornhill's and Gangestad's investigation of human attractiveness and its role in the evolution of human mating began interestingly enough. In 1990, Thornhill had just returned from Japan and Germany where he had been studying scorpion flies.
Biologists consider bilateral symmetry to be a marker of developmental stability.
The tendency in the natural selection of any animal is to develop perfectly matching eyes, wings, legs, arms, feet, ears, etc. However, balanced development can be thrown off course by mutations, toxins, and disease. More resilient individuals can more readily overcome these setbacks and better maintain their symmetry. Such resiliency has a genetic basis and can in part be inherited. Consequently, bilateral symmetry can be seen as a health certification, and as such, a logical reason for females to select males as mates, at least in the case of scorpion flies.