Document Type



Elliptocytosis/ovalocytosis is a dominant and common Mendelian trait in Malaysian aborigines. Epidemiologic and in vitro studies indicate the trait provides resistance to malaria. This report considers the hypothesis that the selective advantage of elliptocytosis in a malarious environm ent includes differential fertility (in the broad sense, including fecundity) as well as differential viability. Individuals with the elliptocytosis trait tend to live longer than those lacking it, thus obtaining an opportunity for higher fertility. Based on analyses of living offspring, mothers with elliptocytosis appear to have larger families than mothers lacking the trait. This fertility differential is only partly accounted for by the difference in mean age between the two groups of mothers. In addition, both groups of mothers have a lower frequency of elliptocytosis offspring than expected on the basis of the malaria hypothesis. Thus, individuals homozygous for the elliptocytosis allele, not clearly identifiable by any assay, may be differentially susceptible to mortality; i.e., elliptocytosis may be a balanced polymorphism with heterozygote advantage. A selection model to account for this possibility is presented.