During their evolutionary history hominins underwent physiological and behavioral changes to cope with and adapt to more open and hotter environments. These changes include increased sweat capacity and loss of hair coverage, but are difficult to pinpoint using the fossil record as such changes do not fossilize. Even bipedalism, the defining hominid characteristic, has been argued by some to be linked with the transition into savanna environments. In a paper, the researchers demonstrate that a group of savanna-dwelling chimpanzees showed significant physiological difficulty when temperatures were high and water was scarce.