"There is a lot of variation in digit ratio and aggression among individuals in both sexes," Ms. Bailey added.

Several studies present evidence that digit ratios are heritable.

It is not clear why digit ratio ought to be influenced by prenatal hormones.

Some authors suggest that digit ratio correlates with health, behavior, and even sexuality in later life.

A study in Germany has found a correlation between digit ratio and male-to-female transsexualism.

Trans women were found to have a higher digit ratio than cisgendered males, but one that was comparable to control females.