transformation" (13) all the variety of life has come into existence. All this diversified life manifestation is the result of a common physicochemical process, the metabolism of the plasma. "Its two most important factors are the physiological functions of adaptation (variation) and heredity; the former is related with metabolism (nutrition and growth), the latter with propagation (transgressive growth)."
All organisms are (14) genealogically related and man's place in nature "is fully understood." There is no room left to doubt (15) that man is in every respect a genuine vertebrate, or, more precisely, a mammal and that he has evolved from this highest family of animals not earlier than the latter part of the Tertiary period. Man (16) is plainly most nearly related to the tailless apes, but none of the living representatives of this group can be considered the direct ancestor of man.
On the contrary, the common ancestors of all these anthropoid apes and man are to be looked for in extinct earlier species of apes of the old world (Pithecanthropus) or in their relatives.
(17) The soul (psyche) of man taken as a distinct supernatural being in both the mystic realms of metaphysics and of theology, has been recognized as the totality of cerebral functions, a discovery brought about chiefly through the astounding progress made in modern biology and particularly in comparative brain-research. The function of the higher soul or thought-organ in man (pronema)—a certain area of the cerebral cortex—takes place perfectly in accordance with the same laws of psycho-physics in the other mammals, and especially in the nearest relatives of man, the anthropoids. This function, of course, ceases at death, and in our time it appears utterly absurd to persist nevertheless in the doctrine of a "personal immortality of the soul."
Like all other functions of the brain (sensation, imagination, ratiocination), the will of man (18) is a physiological function of this central nervous organ and is dependent on the latter's anatomic structure. The peculiar individual potentialities of the human brain, partly inherited from ancestors and partly acquired through adaptation in the life of individuals, necessarily determine the will. The ancient doctrine of a "free will," indeterminism, therefore appears untenable and must give room to the opposite doctrine of determinism.
(19) If under the ambiguous term of "God" is understood a personal "Sublime Being," a ruler of the cosmos who, after the fashion of man, thinks, loves, generates, rules, rewards and punishes, etc., such an anthropomorphic God must be relegated to the realm of mystic imagery—no matter whether this personal God be invested with a human form or be assumed as an invisible spirit or as a "gaseous vertebrate." For modern science the idea of God is scrutable only so far as we recognize in this "God" the last irrecognizable cause of things, the unconscious hypothetical "first cause of substance."All these theses are Haeckel's expression of a complete acceptance of the evolution conception and its apparently logical conclusions. Haeckel's constant question is "Do you accept the evolution conception of the world and life?" His constant rejoinder to any who answer Yes is: "Well, then you have to accept, if you are scientifically and philosophically honest, my monism. There is no escape from it."
