While many studies have compared Tibetans and low-altitude born Han living at high altitude, few have carefully controlled the chronological age at which lowlanders migrated, the length of time they had lived at high altitude, their nutrition, and their socio-economic status. This has produced an array of results that frequently do not support the hypothesis that Tibetans and Han show fundamental differences in their response to hypoxia. Unlike the situation in the Andes, only one study has tested the developmental adaptation hypothesis on the Qinghai-Tibetan plateau. This study shows that Tibetans and Han of the same age, who were born and raised in the same towns at the same altitudes, show considerable overlap in the individual distribution of [Hb], SaO2 and lung volumes. These results indicate that second-generation Han make substantial developmental adjustments to hypoxia that are not reflected in studies of first-generation migrants. Thus, there is a great need for further developmental studies to determine whether and/or how Han and Tibetan responses to hypoxia diverge, as well as for studies exploring whether Han and Tibetans who show similar responses also share genetic adaptations. Am. J. Hum. Biol. 25:169–178, 2013. © 2013 Wiley Periodicals, Inc.