Page:The Science of History and the Hope of Mankind.djvu/25

 HE development of all living organisms is effected through certain energies and substances that are conducive to the growth and manifestation of life. It is the environment and physical surroundings that supply these life-sustaining factors to the organisms. And this physical universe is not only the feeder and sustainer of living beings, it is also the field of their activity as well as the abode in which they grow and reproduce themselves. Hence the action and reaction between the living organism and the environment regulate all the conditions of its life-history.