To verify this prediction, Prokosch et al. measured the right and left foot width, ankle width, wrist width, elbow width, ear width, ear length, index finger length, middle finger length, third finger length, and little finger length of 78 male subjects.
Each subject also completed standard tests of general intelligence, including Raven’s matrices, WAIS III vocabulary, Shipley vocabulary, and digit span (forwards and backwards).
The results showed that bodily symmetry was correlated with all the measures (except for digit span), and that the size of each correlation was related to how strongly each of these measures predicts general intelligence. In other words, body symmetry more strongly predicts intelligence than brain size, nerve conduction velocity, reaction time reliability, and a number of other measures. (This result was replicated this year in a study where symmetry of finger length and palm width had the strongest relationship with intelligence.)