282 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 
increasing complexity, sustained through the interchange of energy. 
Darwin’s principle of the survival or elimination of various forms of 
living energy is, in fact, adumbrated in the survival or elimination of 
various forms of lifeless energy as witnessed among the stars and 
planets. In other words, Darwin’s principle operates as one of the 
causes of evolution in making the lifeless and living worlds what they 
now appear to be, but not as one of the energies of evolution. Selec- 
tion merely determines which one of a combination of energies shall 
survive and which shall perish. 
The complex of four interrelated sets of physicochemical energies 
which I have previously set forth as the most fundamental biologic 
scheme or principle of development may now be restated as follows: 
In each organism the phenomena of life represent the action, reaction, 
and interaction of four complexes of physicochemical energy, namely, 
those of (1) the Inorganic Environment, (2) the developing Organism 
(protoplasm and body-chromatin), (3) the germ or Heredity-Chromatin, 
(4) the Life Environment. Upon the resultant actions, reactions, and 
interactions of potential and kinetic energy in each organism Selection 
1s constantly operating wherever there is competition with the correspond- 
ing actions, reactions, and interactions of other organisms. 
This principle I shall put forth in different aspects as the central 
thought of these lectures, stating at the outset and often recurring 
to the admission that it involves several unknown principles and 
especially the largely hypothetical question whether there is a relation 
between the action, reaction, and interaction of the internal energies 
of the germ or heredity-chromatin with the external energies of the 
inorganic environment, of the developing organism, and of its life 
environment. In other words, while this is a principle which largely 
governs the Organism, it remains to be discovered whether it also 
governs the causes of the Evolution of the Germ. 
As observed in the preface we are studying not one but four 
simultaneous evolutions. Each of these evolutions appears to be 
almost infinite in itself as soon as we can examine it in detail, but of 
the four that of the germ or heredity-chromatin so far surpasses all 
the others in complexity that it appears to us infinite. 
The physicochemical relations between these four evolutions, 
including the activities of the single and of the multiplying organisms 
of the Life Environment, may be expressed in diagrammatic form as 
follow: 
