Extrapair paternity is a crucial parameter for evolutionary explanations of reproductive behavior. Early studies and human testis size suggest that human males secure/suffer frequent extrapair paternity. If these high rates are indeed true, it brings into question studies that use genealogies to infer human life history and the history of diseases since the recorded genealogies do not reflect paths of genetic inheritance. We measure the rate of nonpaternity in an old Afrikaner family in South Africa by comparing Y-chromosome short tandem repeats to the genealogy of males. In this population, the nonpaternity rate was 0.73%. This low rate is observed in other studies that matched genealogies to genetic markers and more recent studies that also find estimates below 1%. It may be that imposed religious morals have led to reduced extrapair activities in some historic populations. We also found that the mutation rate is high for this family, but is unrelated to age at conception.