The biological and behavioural variations in recent human populations are explored in relation to the environmental stresses which developed during human evolution. While early hominid evolution produced a form genetically adapted to the climate and biota of the hot savannah, hominid populations from Homo erectus onwards adapted to an increasingly diversified combination of natural and cultural stresses. It is suggested that this diversity of stresses was a result of an interlocked process whereby populations, in adapting to new environments, created new stresses which evoked further adaptive responses. Examples of how biological and cultural adaptations created new stresses are offered. The adaptation of the Amerindians to the environment of the high Andes is reviewed to illustrate the complex biological and cultural interactive mechanisms of an environmental adaptation. While the spread of modern urban industrial society appears to be reducing the diversity of stresses, results from a study of Samoans show that the nature and intensity of biological stress encountered by modernising populations is regulated by the adaptations previously made to the traditional environment. It is concluded that the rapid changes in stress associated with modern society may well test the limits of the human adaptive capacity.
