"In addition to advances in skeletal structure and stabilization, adaptations that led to increased efficiency in dissipation of heat were instrumental in the evolution of endurance running in Homo. The duration for which an animal can run is determined by its capacity to release more heat than is produced to avoid lethal temperatures.
Evaporative Cooling: The majority of mammals, including humans, rely on evaporative cooling to maintain body temperature.
Sweating vs. Panting: Most medium-to-large mammals rely on panting, while humans rely on sweating, to dissipate heat. Advantages to panting include cooler skin surface, little salt loss, and heat loss by forced convection instead of reliance on wind or other means of convection. On the other hand, sweating is advantageous in that evaporation occurs over a much larger surface area (the skin), and it is independent of respiration, thus is a much more flexible mode of cooling during intense activity such as running.
Human Advantages: Because human sweat glands are under a higher level of neuronal control than those of other species, they allow for the excretion of more sweat per unit surface area than any other species. Heat dissipation of later hominins was also enhanced by the reduction in body hair.[5] By ridding themselves of an insulating fur coat, running humans are better able to dissipate the heat generated by exercise.
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http://en.wikipedia.org/wiki/Endurance_ ... hypothesis