Vol. 8. 1922 
BIOLOGY: A. J. LOTKA 
147 
CONTRIBUTION TO THE ENERGETICS OF EVOLUTION'' 
By Alfred J. Lotka 
School of Hygiene and Public Health, Johns Hopkins University 
Communicated, May 6, 1922 
It has been pointed out by Boltzmann^ that the fundamental object of 
contention in the hfe-struggle, in the evolution of the organic world, is 
available energy. ^ In accord with this observation is the principle^ that, 
in the struggle for existence, the advantage must go to those organisms 
whose energy-capturing devices are most efficient^ in directing available 
energy into channels favorable to the preservation of the species. 
The first effect of natural selection thus operating upon competing 
species will be to give relative preponderance (in number or mass) to 
those most efficient in guiding available energy in the manner indicated. 
Primarily the path of the energy flux through the system will be affected. 
But the species possessing superior energy-capturing and directing de- 
vices may accomplish something more than merely to divert to its own 
advantage energy for which others are competing with it. If sources 
are presented, capable of supplying available energy in excess of that 
actually being tapped by the entire system of living organisms, then an 
opportunity is furnished for suitably constituted organisms to enlarge the 
total energy flux^ through the system. Whenever such organisms arise, 
natural selection will operate to preserve and increase them. The re- 
sult, in this case, is not a mere diversion of the energy flux through the 
system of organic nature along a new path, but an increase of the total 
flux through that system. 
Again, so long as sources exist, capable of supplying matter, of a charac- 
ter suitable for the compositon of living organisms, in excess of that 
actually embodied in the system of organic nature, so long is opportunit}^ 
furnished for suitably constituted organisms to enlarge the total mass of 
the system of organic nature. Whenever such organisms arise, natural 
selection will operate to preserve and increase them, provided always 
that there is presented a residue of untapped available energy. The re- 
sult will be to increase the total mass of the system, and, with this total 
mass, also the total energy flux through the system, since, other things 
equal, this energy flux is proportional to the mass of the system. 
Where a limit, either constant or slowly changing,^ is imposed upon the 
total mass available for the operation of life processes, the available energy 
per unit of time (available power) placed at the disposal of the organisms, 
for application to their life tasks and contests, may be capable of increase 
by increasing the rate of turnover of the organic matter through the life 
cycle. So, for example, under present conditions,^ the United States 
produce annually a crop of primary and secondary food amounting to 
