Document Type



The acid phosphatase locus (ACPl) is a classical polymorphism that has been surveyed in hundreds of human populations worldwide. Among individuals of European ancestry, the ACP J *C aUele occurs with an average frequency of approximately 0.05, whereas it is nearly absent in all other human populations. It has been hypothesized that this allele is maintained by overdominant selection among European populations. Here, we analyze ACPI proteiD polymorphism data from more than 50,000 individuals previously surveyed in 67 populations across Europe as well as inheritance data from more than 6,000 European parent-offspring pairs to assess the signature of natural selection currently acting on this allele. Although we see a significant excess of ACP 1 *C heterozygotes relative to Hardy-Weinberg expectations, we find no evidence that natural selection favors ACP l*C heterozygotes. Instead, ACP 1 *C appears to have a strongly deleterious and recessive fitness effect. We observed only 48.9% of expected homozygous offspJing from heterozygous parents and significantly fewer homozygotes than expected within populations. Because parent-offspring pairs indicate a significant deficiency of ACP l*C homozygotes, we infer that viability selection is acting on ACP 1 *C homozygotes very early in life, perhaps before birth. We estimate that approximately 1.2% of all couples of European ancestry are composed of individuals who both can'y the APC I *C allele. As such, selection against ACP 1 *C homozygotes may represent a nonnegligible contribution to the overall number of spontaneous abortions among women of European ancestry and may cause substantial fertility reductions among some combinations of parental genotypes.