An Association Between the Kinship and Fertility of Human Couples (pdf) Science (2008), 391: 813-816 In which we learn that true love could be where the 3rd or 4th cousin is… – – – ABSTRACT: Previous studies have reported that related human couples tend to produce more children than unrelated couples but have been unable to determine whether this difference is biological or stems from socioeconomic variables. Our results, drawn from all known couples of the Icelandic population born between 1800 and 1965, show a significant positive association between kinship and fertility, with the greatest reproductive success observed for couples…