At least one researcher, Dr. Randy Thornhill of the University of New Mexico in Albuquerque, suspects that symmetry is very important to the females of one advanced species: human beings. With his colleagues Karl Grammer and Steven Gangestad, Thornhill is trying to apply the evolutionary principles they've developed in their work on scorpion flies and other species to people.
They have taken photographs of male and female college students, put the pictures into computers and digitalized them for precise measurements. They then gauged the relative symmetry of the faces by putting points on key features: the outer corners of the eyes, inner corners of the eyes, the cheekbones, the outer corners of the lips, the outer edge of each nostril and the outer points of the jaw.Lines are then drawn to connect one dot to its opposite mate, and the midpoint of that line is calculated. On a perfectly symmetrical face, all the midpoints of those lines meet and form one vertical line down the center of the face. Any deviation from that vertical line is a measure of horizontal asymmetry. (Both vertical and horizontal asymmetry were scored; the examples shown are marked to study horizontal asymmetry.)
The scientists showed the computerized images to other students and asked them to rate the subjects by degree of attractiveness. They learned that, yes, the most symmetrical faces are also considered the most appealing. In particular, men ranked the symmetrical female faces to be most attractive.
However, the scientists went further, asking their photographed students to fill out questionnaires about when they first lost their virginity, and how many sex partners they had had, information that can be considered a somewhat crude estimation of so-called genetic fitness, that is, the likelihood of passing one's genes into the pool. "It worked like a charm," said Thornhill. "Those with greatest facial symmetry lose their virginity earlier, and their number of partners is higher."
Of course, Thornhill admitted that preliminary and small-scale results like this must be taken with grains if not shakers of salt, for messy human considerations invariably interfere with theory. A simple thing like the fear of AIDS, for example, may well prevent the owner of a pleasingly symmetrical face from taking advantage of all the mating opportunities that arise.