The evolutionary basis of thermoregulation and exercise performance.

The evolutionary history of mammals, but more specifically humans, indicates that heat stress was a decisive and powerful selection pressure. There is good evidence that early hominids had to adapt to a changing environment by assuming an upright posture and consequently bipedalism. Because of further distances between food sources and the need for prolonged hunting, bipedal locomotion over longer distances required higher aerobic capacities and as a consequence an increase in endogenous heat production. A cooling mechanism to balance heat loads was essential for survival and adaptations by other bodily systems such as the brain must have developed to deal with the increased heat stress. This chapter discusses the evolutionary forces which are thought to have produced the thermoregulatory system used by modern day humans in exercise performance. A particular feature that has been overlooked by thermal physiologists is the way in which mammals use the thermoregulatory system to anticipate thermal limits during physical activity and thus avoid physiological catastrophe.