For those who are wondering why there're pictures of our fingers here. This is the reason:
Research out of the University of Liverpool in England indicated the size of a man’s ring fingers and genitals are directly related to how much testosterone he received in the womb. The more testosterone he received, the longer his penis.
In “Sex on the Brain,” Dr. Daniel Amen further explains how this measures up. If a man’s ring fingers are longer than his index fingers, this means there were healthy testosterone levels in the womb. If the ring fingers are the same size or smaller than the index fingers, then the male received lower levels of testosterone. Thus, by knowing this information, you can estimate the length of his member.