Evolution of Litter Size in Primates

Despite strong selection for low reproductive turnover in primates in general, there is a considerable number of species in which multiple births regularly occur. Since multiple births are limited to the smallest species in both suborders, Strepsirhini and Haplorhini, it appears that restrictions of scaling set a threshold for maternal size below which the production and delivery of single offspring is intolerable. While multiple births in the smallest strepsirhines most probably represent a primitive character state, multiple births in the smallest haplorhines (callitrichids) are viewed as a derived condition and as a correlate of phyletic dwarfism.