Vol. 8, 1922 
BIOLOGY: A. J. LOTKA 
153 
tion were equal; the units in the new statistical mechanics will be energy 
transformers subject to irreversible collisions of peculiar type — collisions 
in which trigger action is a dominant feature: 
When the beast of prey A sights its quarry B, the latter may be said to 
enter the field of influence of A, and, in that sense, to collide with A. The 
energ\' that enters the eye of A in these circumstances may be insignificant, 
but it is enough to work the relay, to release the energy for the fatal en- 
counter. And because evolution works with armies built up of similar 
units, the seemingly erratic workings of the relay mechanism (in which ac- 
tion and reaction are not equal, and seem subject to no simple general 
law) are not, in effect, erratic, but range themselves according to law and 
order, for those species of units, those types of transformers, are picked 
out for survival, whose mechanism possesses certain definite properties. 
Thus the principle of natural selection makes its entry into dynamics. 
Further elaboration of these concepts must be reserved for a future 
occasion. 
In systems evolving toward a true equilibrium (such as thermally and 
mechanically isolated systems, or the isothermal systems of physical chem- 
istry) , the first and vSecond laws of thermodynamics suffice to determinate 
at any rate the end state; this is, for example, independent of the amount 
of any purely catalytic substance that may be present. The first and the 
second law here themselves function as the laws of selection and evolution, 
as has been recognized by Perrin^ and others, and exemplified in some 
detail by the writer, for the case of a monomolecular reversible reaction.^'* 
But systems receiving a steady supply of available energy (such as the 
earth illuminated by the sun) , and evolving, not toward a true equilibrium, 
but (probably) toward a stationary state, the laws of thermodynamics are 
no longer sufficient to determine the end state ; a catalyst, in general, does 
affect the final steady state. Here selection may operate not only among 
components taking part in transformations, but also upon catalysts, in 
particular upon auto -catalytic or auto-catakinetic constituents of the sys- 
tem. Such auto-catakinetic constituents are the living organisms, and 
to them, therefore the principles here discussed, apply. 
That the principle of selection is competent to yield information be- 
yond the scope of the laws of thermodynamics has been very clearly set 
forth, independently, by H. Guilleminot.^^ The present writer has 
long realized that the principle is capable of such application; that it 
functions, as it were, as a third law of thermodynamics (or a fourth, if the 
third place be given to the Nernst principle). If he has not, before this 
date, explicitly stated the case, this is mainly because his writings have 
followed a definite, systematic plan, announced in his early publications.^^ 
Viewing evolution as a change in the distribution of matter among the 
components of a physical system, the study of evolution naturally di- 
