Cuckoldry: Reality or Urban Legend?

New York Times (Apr. 8, 2016): Fathered by the Mailman? It's Mostly an Urban Legend, by Carl Zimmer:

Stories about adultery and uncertainty about paternity permeate mass media and popular culture.  At the dawn of the era of DNA testing, some data suggested that up to 30% of the children born to married couples were the product of adultery.  But those data involved requests by husbands who suspected their wives had extramarital paramours.  New research suggests that births of children from wives' adulterous liaisons actually occurs very seldom. 

The new study looks at inheritance of the Y chromosome.  The Y chromosome is passed down in almost identical form from fathers to sons.  By studying the chromosomes of living related men in various countries (Spain, Italy, Germany, Mali and Belgium), researchers came up with an adulterous paternity rate of less than one percent. 

One reflection of the low rate may lie in the inefficacy of human sperm to compete for fertilization as compared to other species'.  "The only way for men to have evolved comparatively ineffectual sperm," according to one researcher, "was for them to have experienced high rates of paternity over time."  She added that better assurances of paternity lead to higher investments of fathers in their children.  These investments have been critical to the survival of the species given that humans are completely helpless when they are born.