After presenting the various theories on the subject of heredity and environment the conclusion presented was that "the known facts of the development of the nervous system in the individual, together with a dynamic understanding of the process of heredity, seems to make clear the fact that there is, indeed, a real and inviolable interdependence between maturation and environmental learning. From the moment that growth has begun in the fertilized ovum until senescence or death, development consists in the alteration of existing structures and functions. Such modification, however, can only occur by the interaction of changing environment. Heredity and environment are not antithetical, nor can they expediently be separated; for in all maturation there is learning: in all learning there is hereditary maturation." (PsycINFO Database Record (c) 2006 APA, all rights reserved)