Dietary change and adaptive evolution of enamelin in humans and among primates

Scans of the human genome have identified many loci as potential targets of recent selection, but exploration of these candidates is required to verify the accuracy of genomewide scans and clarify the importance of adaptive evolution in recent human history. We present analyses of one such candidate, enamelin, whose protein product operates in tooth enamel formation in 100 individuals from 10 populations. Evidence of a recent selective sweep at this locus confirms the signal of selection found by genomewide scans. Patterns of polymorphism in enamelin correspond with population-level differences in tooth enamel thickness, and selection on enamel thickness may drive adaptive enamelin evolution in human populations. We characterize a high-frequency nonsynonymous derived allele in non-African populations. The polymorphism occurs in codon 648, resulting in a nonconservative change from threonine to isoleucine, suggesting that the allele may affect enamelin function. Sequences of exons from 12 primate species show evidence of positive selection on enamelin. In primates, it has been documented that enamel thickness correlates with diet. Our work shows that bursts of adaptive enamelin evolution occur on primate lineages with inferred dietary changes. We hypothesize that among primate species the evolved differences in tooth enamel thickness are correlated with the adaptive evolution of enamelin.