Man not only survives and functions in his environment, he shapes it and he is shaped by it.

Any attempt to shape the world and modify human personality in order to create a self-chosen pattern of life involves many unknown consequences. Human destiny is bound to remain a gamble, because at some unpredictable time and in some unforeseeable manner nature will strike back. The multiplicity of determinants which affect biological systems limits the power of the experimental method to predict their trends and behavior.

Human diversity makes tolerance more than a virtue; it makes it a requirement for survival.

Social evolution may be the result of intention, but it rarely, if ever, produces the result intended.

With reference to life there is not one nature; there are only associations of states and circumstances, varying from place to place and from time to time.

But solving problems of disease is not the same thing as creating health and happiness. (...) Health and happiness are the expression of the manner in which the individual responds and adapts to the challenges that he meets in everyday life.

Whatever his inhibitions and tastes, Western man believes in the natural holiness of seminudism and raw vegetable juice, because these have become for him symbols of unadultered nature.