Adaptation to warm climates

Abstract

This is characteristically found in the rain forest belt which more or less follows the Equator round the world through Central Africa, India and the Pacific Islands and South America. It is a monotonous climate with little variation in temperature day or night or thoughout the year. The dry bulb temperature rarely exceeds 90 F. and a wet bulb is not far behind it and frequently at night the humidity may be 100%. Rain forest protects the area from wind and the air is invariably still. Because of the high humidity man cannot lose heat through evaporation and must rely on conduction, convection and radiation, which are slow processes and thus after exercise many hours elapse before the body temperature returns to normal. It is a climate too which discourages activity and the inhabitants are quite naturally lazy especially as there is often an abundance of food. Furthermore the lack of contrast between day and night and winter and summer removes the stimulus of change which monotony in practise leads to a much higher incidence of psychiatric disease. In a serious of experiments comparing the stress of the jungle and desert climates it was found that the excretion of 17 keto-steroids in the urine was increased. In the Service during the war the invaliding rate from this climate for psychological upset was much higher than elsewhere.