Fig. 1. Main themes of temporal patterns of hypoxia adaptation. (1) Immediate or constitutive, exemplified by the northern painted turtle, Chrysemys picta. (2) Developmental, as in the relative hypoxia of the in utero environment. (3) Slow or chronic, as exemplified by human adaptation to high-altitude hypoxia over the course of many days (photo courtesy of R. Boutilier).