152 
BIOLOGY: A. J. LOTKA 
Proc. N. a. S. 
plete information, or else our deliberate ignoring of some of the factors 
that actually do determine the course of events. Admitting, however, 
broadly, the directing influence of life upon the world's events, within the 
limits imposed by the Mayer- Joule and the Carnot-Clausius principles, 
it would be an error to suppose that the faculty of guidance which the es- 
tablished laws of thermodynamics thus leave open, is a peculiar preroga- 
tive of living organisms. If these laws do not fully define the course of 
events, this does not necessarily mean that this course, in nature, is act- 
ually indeterminate, and requires, or even allows, some extra-physical 
influence to decide happenings. It merely means that the laws, as form- 
ulated, take account of certain factors only, leaving others out of consider- 
ation; and that the data thus furnished are insufficient to yield an unam- 
biguous answer to our enquiry regarding the course of events in a physical 
system. Whether life is present or not, something more than the first 
and second laws of thermodynamics is required to predict the course of 
events. And, whether life is present or not, something definite does happen y 
the course of events is determinate, though not in terms of the first and 
second laws alone. The "freedom" of which living organisms avail 
themselves under the laws of thermodynamics is not a freedom in fact, 
but a spurious freedom^ arising out of an incomplete statement of the phys- 
ical laws applicable to the case. The strength of Carnot's principle is 
also its weakness : it holds true independently of the particular mechanism 
or configuration of the energy transformer (engine) to which it is applied; 
but, for that ver}^ reason it is also incompetent to yield essential informa- 
tion regarding the influence of mechanism upon the course of events. In 
the ideal case of a reversible heat engine the efficiency is independent of 
the mechanism. Real phenomena are irreversible; and, in particu- 
lar, trigger action,^ which plays so important a role in life processes, is a 
typically irreversible process, the release of available energy from a "false" 
equilibrium. Here mechanism is all-important. To deal with problems 
presented in these cases requires new methods,^ requires the introduction, 
into the argument, of new principles. And a principle competent to ex- 
tend our systematic knowledge in this field seems to be found in the prin- 
ciple of natural selection, the principle of the survival of the fittest, or, to 
speak in terms freed from biological implications, the principle of the 
persistence of stable forms. 
For the battle array of organic evolution is presented to our view as 
an assembly of armies of energy transformers — accumulators (plants), 
and engines (animals); armies composed of multitudes of similar units, 
the individual organisms. The similarity of the units invites statistical 
treatment, the development of a statistical mechanics of which the units 
shall be, not simple material particles in ordinary reversible collision of 
the type familiar in the kinetic theory, collisions in which action and reac- 
