Beverly Strassmann is quoted about her work gathering data on paternity rates in this New York Times article:

Fathered by the Mailman? It’s Mostly an Urban Legend

Beverly I. Strassmann, a University of Michigan anthropologist whogathered the data on paternity rates in Mali, agreed that widespread cuckoldry “was an urban legend. It seemed to have a life of its own.

”The evidence of low rates of cuckoldry comes not just from gene studies, she noted. In species where females mate with many males, the males tend to evolve sperm that are good at competing for fertilization. The males may produce large amounts of sperm, for example, and a high percentage swim well.

Humans, however, don’t rate in the sperm department.“It’s of amazingly low quality,” Dr. Strassmann said. “Half the sperm can be duds; they can have two heads; they can be defective in all sorts of ways.”