In some forms of mutilation, the handicap to sperm competition is obvious. There is subincision, for example, where cuts are made to the base of the penis. This causes sperm to be ejaculated from the base rather than the end, and is performed in several Aboriginal Australian societies, says Wilson.

In some African and Micronesian cultures, young men have one of their testicles crushed.

Male genital mutilation makes it less likely that a male will manage to father a child with another man's wife, Wilson says.
Home advantage

Circumcision is one of the less painful forms of mutilation, but it is also less effective at reducing sperm competition. Wilson suggests, however, that the lack of a foreskin could make insertion or ejaculation slower, meaning brief, illicit sex is less likely to come to fruition and lead to a pregnancy.

Younger men, he says, willingly submit to having their reproductive ability reduced because they benefit socially from the older men, by forming allian