Vol. 8, 1922 
BIOLOGY: A. J. LOTKA 
151 
with a change in the distribution of matter among the several species composing the 
system, would probably play a subordinate role ; in contrast with the condition of affairs 
familiar in ordinary physico-chemical systems. This is an obvious inference from the 
observation that the several species of organisms are distinguished much more by struc- 
tural differences than by differences in chemical composition. 
^2 Ostwald, W., Lehrbuch der allgemeinen Chemie, 1892, vol. 2, p. 37; Siebel, J. E 
Compend of Mechanical Refrigeration, 1915, p. 88. For a discussion of the validity and 
limitations of Ostwald's principle see Helm G., Die Energetik, 1898, pp. 248; Neumann, 
C, Leipziger Berichte, 1892, p. 184. 
1^ That living organisms may be capable of retarding the energy flux through the sys- 
tem of nature was suggested by the present writer in Ann. Naturphil., 1910, p. 60. 
14 Johnstone, J., The Mechanism of Life, 1921, p. 220. 
NATURAL SELECTION AS A PHYSICAL PRINCIPLE'' 
By AIvFred J. LoTKA 
ScHOOi. OF Hygiene and Pubeic Health, Johns Hopkins University 
Communicated May 6, 1922 
In a paper presented concurrently with this, the principle of natural 
selection, or of the survival of the fittest (persistence of stable forms), 
is employed as an instrument for drav^ing certain conclusions regarding the 
energetics of a system in evolution. 
Aside from such interest as attaches to the conclusions reached, the 
method itself of the argument presents a feature that deserves special 
note. The principle of natural selection reveals itself as capable of yield- 
ing information which the first and second laws of thermodynamics are 
not competent to furnish. 
The two fundamental laws of thermodynamics are, of course, insuffi- 
cient to determine the course of events in a physical system. They tell 
us that certain things cannot happen, but they do not tell us what does 
happen. 
In the freedom which is thus left, certain writers have seen the opportu- 
nity for the interference of life and conciousness in the history of a physical 
system. So W. Ostwald^ observes that "the organism utilizes, in many- 
fold ways, the freedom of choice among reaction velocities, through the 
influence of catalytic substances, to satisfy advantageously its energy re- 
quirements." Sir Oliver Lodge also, has drawn attention to the guidance^ 
exercised by life and mind upon physical events, within the limits imposed 
by the requirements of available* energy. H. Guilleminot^ sees the in- 
fluence of life upon physical systems in the substitution of guidance by 
choice in place of fortuitous happenings, where Carnot's principle leaves 
the course of events indeterminate. As to this, it may be objected 
that the attribute of fortuitousness is not an objective quality of a given 
event. It is the expression of our subjective ignorance, our lack of com- 
