"Since the beginning of civilization, organized societies have had to put pressures on human beings of the sake of the functioning of the social organism. The kinds of pressures vary greatly from one society to another. Some of the pressures are physical (poor diet, excessive labor, environmental pollution), some are psychological (noise, crowding, forcing human behavior into the mold that society requires). In the past, human nature has been approximately constant, or at any rate has varied only within certain bounds."