Africa is believed to be the cradle of the most recent ancient ancestors of modern humans and estimates indicate their expansion out of Africa began about 92,000 to 156,000 years ago. Based on geographic, anthropological, linguistic, and ethnic criteria, evolutionists divide human populations into Negroid, Mongoloid, and Caucasoid races where race is defined as a large group of individuals that has a significant fraction of its genes in common and can be distinguished by its gene pool. Population frequencies of many pharmacogenetic traits depend on race or ethnic specificity and may differ greatly within and between raciogeographic groups. Pharmacogenetic variants may be shared by different populations if they occurred before evolutionary separation, but may be specific for a population if they occurred after separation. Person-to-person differences in drug disposition, efficacy, and toxicity across ethnogeographic populations are closely associated with differences in allelic frequencies of genes that determine these events. These differences are valuable as starting points for pharmacogenetic research, for individualization of drug therapy, and for improving the efficiency of development and clinical trials of new drugs. Culturally specific risks may be encountered in diverse study populations in conducting research to discover ethnic variation, and investigators will improve their chances of assessing specific benefits if they are prepared to modify their research design and conduct to accommodate them.

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