F 
ù 

THE 
AMERICAN NATURALIST 


Vor. XXXVI. May, 1902. No. 425. 


THE LAW OF ADAPTIVE RADIATION. 
` HENRY FAIRFIELD OSBORN. 
Oxe of the essential features of divergent evolution as 
conceived in the branching system successively developed by 
Lamarck, Darwin, Huxley, and Cope has béen termed by the 
writer * adaptive radiation." This term seems to express most 
clearly the idea of differentiation of habit in several directions 
from a primitive type, as shown in the accompanying diagrams. 
The law is a familiar one ; it results in the formation of analo- 
gous radii in different groups of animals. The first compre- 
hensive illustration of the law known to the writer is that 
under the headings ** Homologous Groups " and * Heterology," 
in Cope's paper of 1868 on the “Origin of Genera," reprinted 
in the Origin of the Fittest (pp. 95-106). This brilliant essay 
is marred only by great confusion in the use of terms; but the 
parallelisms in unrelated groups of amphibians and of mam- 
mals such as marsupials and placentals, as first observed by 
Owen, are clearly brought out. 
In the present paper citations from earlier essays of my own 
may be given bearing upon general adaptive radiation and the 
independent production of analogous radii under the convergent 
353 
