Abstract
Formulae are derived for the extent to which the size of the group from which marriage partners are chosen affects the availability of marriage partners, under monogamy and endogamy, when group membership and appropriate sex are the only criteria for eligibility, and when males and females are equally likely to become group members. The expected proportion of group members unable to find eligible partners under these conditions decreases monotonically as group size increases, approaching a limit of zero as the group size becomes large, but becomes substantial for small groups. These results give minimal estimates of the effects of group size: the introduction of additional constraints-incest taboos, requirements that couples have similar age or social status, etc.-could only increase the proportion unable to find acceptable partners. Possible extensions to more complex marriage models are discussed.
