Once upon a time, people often said that ~10% of children had a biological father other than their nominal father, usually called false paternity or nonpaternity. This notion was particularly common in sociobiological circles. There were others who thought the same: Robert Heinlein once said that “casual bastardy is far in excess of that ever admitted.” Of course that was said by a character in one of his novels, but I’ll bet he meant it.
In the places and times where we have good numbers, they were clearly wrong. They’re wrong about contemporary rates, and wrong over the past thousand years or so. Hard to say about the Pleistocene.
Here are some good numbers from recent studies:
Contemporary Germany: 1% From checking for HLA type in medical cases.
contemporary Switzerland: 0.83%
Contemporary Iceland 1.49% (from DeCode)
Contemporary Dogon, in Mali. Mildly polygynous. : 1.8%
Contemporary Bushmen (< 2%) (Original source was intoxicated, as usual. Intermediate source was intoxicated and crazy. )
Patronymics & genealogical studies (gives info over the past few hundred years)
Let assume that those West African populations reported average paternal ages of ~46 have 10x higher false paternity than any reliable number ever measured: say 20%. Shit, they might: we don't have any good measurements. I was going to say that I'd probably have a good horseback feel for this if I'd grown up in Ghana, but maybe not: professors who grew up here often don't.
Then average paternal age would be 40.8, still higher than almost anywhere else, other than Australian Aboriginals.
Parenthetically, one might wonder why the ev psych types (and RAH, and Jared Diamond) embraced such inaccurate notions about their own societies.