Significance Native Americans are neglected in human genetics studies, despite recent interest in the study of ancient DNA of their ancestors. Our findings on Andean and Amazonian populations exemplify how the current pattern of genetic diversity in human populations is influenced by the interaction of history and environment. In the present case, this pattern is influenced by 1) altitudinal and climatic differences among the northern, lower, and fertile Andes versus the southern, higher, and arid Andes and 2) the sharp differences between the Andean highlands and the Amazon lowlands, where natural selection and other evolutionary forces acted for millennia, shaping differences in the frequencies of genetic variants related to immune response, drug response, and cardiovascular and hematological functions.