Introduction
With such an attitude towards human nature the anthropologist listened to the current comment upon adolescence. He heard attitudes which seemed to him dependent upon social environment—such as rebellion against authority, philosophical perplexities, the flowering of idealism, conflict and struggle—ascribed to a period of physical development. And on the basis of his knowledge of the determinism of culture, of the plasticity, of human beings, he doubted. Were these difficulties due to being adolescent or to being adolescent in America?
For the biologist who doubts an old hypothesis or wishes to test out a new one, there is the biological laboratory. There, under conditions over which he can exercise the most rigid control, he can vary the light, the air, the food, which his plants or his animals receive, from the moment of birth throughout their lifetime. Keeping all the conditions but one constant, he can make accurate measurement of the effect of the one. This is the ideal method of science, the method of the controlled experiment, through which all hypotheses may be submitted to a strict objective test.
Even the student of infant psychology can only partially reproduce these ideal laboratory conditions. He cannot control the pre-natal environment of the child whom he will later subject to objective measurement. He can, however, control the early environment of the child, the first few days of its existence, and decide what sounds and sights and smells and tastes are to
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