Anomalous and selective DNA mutations of the Old World monkey alpha-globin genes.

It has been a widely accepted hypothesis that the molecular clock slows down during evolution of higher primates. By molecular cloning and nucleotide sequence comparison of a rhesus macaque alpha-globin gene to its homologs in man, orangutan, olive baboon, and other mammals, we demonstrate a burst of evolution of the baboon alpha-globin gene since its separation from the rhesus macaque. This mutation burst has occurred only at the nonsynonymous sites but not the synonymous sites. Its magnitude is at least 10-fold higher than the synonymous substitution rates in higher primates and as high as the synonymous substitution rates of the rodent lineage. On the contrary, the rate of synonymous site substitutions in the alpha-globin genes of either the rhesus macaque or the olive baboon is several times slower than that of human. Our data demonstrate an anomalous exception to the slow rates of molecular evolution in higher primates and provide strong evidence for a recently accelerated evolution of a primate globin gene under an as yet unknown selective force(s).