Vol.. 8, 1922 
BIOLOGY: A. J. LOTKA 
149 
selection to operate in the direction indicated, namely so as to increase the 
total mass of the system, the rate of circulation of mass through the sys- 
tem, and the total energy flux through the system. If this condition is sat- 
isfied, the law of selection becomes also the law of evolution : 
Evolution, in these circumstances, proceeds in such direction as to make 
the total energy flux through the system a maximum compatible with the 
constraints. 
We have thus derived, upon a deductive basis, at least a preliminary 
answer to a question proposed by the writer in a previous publication. 
It was there pointed out that the influence of man, as the most successful 
species in the compedtive struggle, seems to have been to accelerate the 
circulation of matter through the life cycle, both by "enlarging the wheel," 
and by causing it to "spin faster." The question was raised whether, in this, 
man has been unconsciously fulfilling a law of nature, according to which 
some physical quantity in the system tends toward a maximum. This is 
now made to appear probable ; and it is found that the physical quantity 
in question is of the dimensions of power, or energy per unit time, as was 
hinted by the writer on an earlier occasion. 
It may be remarked that the principle of maximum energy flux here 
set forth bears a certain outward resemblance to a principle enunciated 
by Ostwald:^^ "Of all possible energy transformations, that one takes 
place, which brings about the maximum transformation in a given time," 
This principle of Ostwald's, however, is based on entirely different grounds 
from those here brought forward. It is not of general applicability, and 
in particular, its application to systems of the kind here considered does 
not appear warranted. 
Addendum. Since the paragraphs above were penned, the writer has 
received from the booksellers a copy of Professor J. Johnstone's book, 
"The Mechanism of Life" (1921), in which (pp. 217-221) that author 
touches on matters closely related to those here discussed. Professor 
Johnstone draws, however, a somewhat different conclusion, namely 
that "In living processes the increase of entropy is retarded. "^^ He points 
out that this is true, primarily, of plants; but that among animals^^ also 
natural selection must work toward the weeding out of unnecessary and 
wasteful activities, and thus toward the conserving of free energy, or, 
what amounts to the same thing, toward retarding energy dissipation. 
This is perhaps not wholly convincing, for the first effect of the advent 
of animal organisms in a world peopled with a purely vegetable population, 
would certainly seem to be an acceleration of the process of dissipation. 
It appears, therefore, that at certain stages in the evolution of the system, 
at the least, life must have tended to increase rather than decrease dis- 
sipation. And even if animals ultimately evolve in the direction of de- 
creased dissipative effect, they still remain essentially a dissipative type, 
