An Association Between the Kinship and Fertility of Human Couples
There has been
long-standing uncertainty about the impact of kinship or
consanguinity between spouses on the total number of offspring they
produce (completed fertility). 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 related at the level of third and fourth cousins. Owing to
the relative socioeconomic homogeneity of Icelanders, and the observation
of highly significant differences in the fertility of couples
separated by very fine intervals of kinship, we conclude that this
association is likely to have a biological basis.