A 2009 study in " Biology Letters " argues : " Sexual differences in 2D : 4D are mainly caused by the shift along the common allometric line with non-zero intercept, which means 2D : 4D necessarily decreases with increasing finger length, and the fact that men have longer fingers than women, " which may be the basis for the sex difference in digit ratios and / or any putative hormonal influence on the ratios.
