Throughout human history, relatively few men seem to have had a greater input into the gene pool than the rest, suggests a study of variations in DNA.
Tens of thousands of years of polygamy has left a mark on our genomes that is a signature that small numbers of males must have mated with lots of females.
Over time, such a pattern will spawn more genetic differences on the X chromosome than other chromosomes. This is because women have two copies of the X, while men only one. In other words, the diversity arises because some men don't get to pass on their genes, while most women do.
"Humans are considered to be mildly polygynous and we descend from primates that are polygynous," says Michael Hammer, a population geneticist at the University of Arizona in Tucson.
Polygyny refers to the practice of males mating with multiple females, and its most common form in humans is polygamy or multiple marriages.