It's been determined that women whose index fingers are much shorter than their ring fingers have high testosterone ...
BBC - Science & Nature - Sex ID - Testosterone
The reason one hand can be very different from the other is that your right hand is the hand you were born with, and your left hand is what you have done with it.
The reason infants already have most of the lines in their hands is because (are you ready?) of fate.
Palmistry is fun to study and think about.