The thermoregulatory advantages of heat storage and shade-seeking behaviour to hominids foraging in equatorial savannah environments

Abstract

Despite the lack of an elaborate brain cooling system, early hominids could probably tolerate slight fluctuations in body temperature, comparable to those experienced by living primates in thermally stressing environments. Estimates are presented of the reductions in drinking water requirements resulting from the use of such heat storage, both of hominids foraging continually throughout the day on the open savannah, and those suspending this behaviour during the most thermally stressing period. The findings show that periods of inactivity can offer substantial thermoregulatory benefits, but only if the animal is able to retreat into the shade. Both strategies appear to be most advantageous in the absence of functional body hair. Together heat storage and shade-seeking can reduce the estimated total daytime drinking water intakes of naked bipeds to less than one half of those maintaining a constant body temperature and remaining continually active in the open. These studies of activity, patterns likely to have been more typical of those normally utilised when foraging on the open savannah, suggest that the selection pressures favouring the evolution of a functionally naked skin by these bipedal primates may have been even greater than previous calculations based solely on continually active hominids indicated.