I did some thinking and think I’ve found a possible cause and affect for the difference, at least in terms of gender. There are a lot of minor differences, physically, between men and women that have to do with historical roles. Women have larger internal organs in relation to their body mass, because they need added functionality for pregnancy. Men have a higher concentration of red blood cells, which allows them to engage in more strenuous physical activity. The elbow joint of men and women are different in that a man’s palm will face his hip when hanging loose, while a woman’s will face back. The difference gives men a better joint angle for throwing, and women a better joint angle for holding a baby.

If you intend to grip something tight, you’ll use the outer three finger braced against the thumb--making the ring finger more important than the index finger. If you are cradling something in your hand, you’ll need more control and dexterity in your thumb and the fingers closest to it. Making the index finger the more important finger. Thus the added length of the ring ringer on men, and the added length of the index finger on women. It’s a minor detail which is all but meaningless given today’s culture, but explains why such a difference exists.