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High rates of celibacy and emigration have been reported for many populations. This failure to mate is expected to increase random inbreeding by decreasing the effective population size. If celibates and emigrants are not a random sample of the population with respect to kinship, however, their failure to mate may decrease nonrandom inbreeding and compensate for the increase in random inbreeding. An algebraic model is developed which predicts the effect of nonrandom failure to mate on genotype distributions, and which can be used to compare that effect with those of consanguinity avoidance and random inbreeding. Data from a small French Caribbean population is used to demonstrate the use of the model. The results indicate that, with regard to maintaining genetic variability within populations, failure to reproduce may often be the most important aspect of mating structure.