>- 
* 
856 The American Naturalist. [October, 
dicate little or no activity of a selective agency in nature, and do point to 
the existence of an especial developmental force acting by a direct influ- 
ence on growth. The action on this force is the acceleration and retarda- 
tion appealed to inthis paper. The force itself was not distinguished until | 
the publication of the essay entitled “ The Method of Creation” [1871], 
where it was named growth-force or bathmism. The energetic action of 
this force accounts for the origin of characters, whether adaptive or non- 
adaptive, the former differing from the latter in an intelligent direction, 
which adapts them to the environment. The numerous adaptive char- 
acters of animals had by that time engaged the attention of the author, 
and he found that they are even more numerous than the non-adaptive. 
Some of the latter were accounted for on the theory of the ‘‘ complement- 
ary location of growth-force. 
We can only consider the “law of acceleration and retarda- 
tion.” Again it behooves us to seek his own definition : 
a. The succession of construction of parts of a complex was originally 
a succession of identical repetitions ; and grade influence merely deter- 
mined the number and location of such repetitions. 
b. Acceleration signifies addition to the number and location of such 
repetitions during the period preceding maturity, as compared with the 
preceding generation, and retardation signifies a reduction of the number 
of such repetitions during the same time.%6 
His meaning may best be inferred from his application to 
mankind. This was done in the following terms in 1872: 
Let an application be made to the origin of the human species. It is: 
scarcely necessary to point out at the start the fact, universally admitted 
by anatomists, that man and monkeys belong to the same order of Mam- 
malia, and differ in those minor characters, generally used to define a 
“ family ” in zoology. 
Now, these differences are as follows: In man we have the large head 
with prominent forehead and short jaws ; short canine teeth without 1m- 
terruption behind (above); short arms and thumb of hand not oppo- 
sable. In monkeys we have the reverse of all these characters. But 
what do we see in young monkeys? A head and brain as large, rela- 
tively, as in many men, with jaws not more prominent than in some 
races ; the arms not longer than in the long-armed races of men, that is, 
a little beyond half way along the femur. * * * Atthis age of the 
individual the distinctive characters are therefore those of homo, with the 
exception of the opposable thumb of the hind foot, and the longer canine 
tooth, * * * 
* Proc. Am, Phil. Soc., 1871; Origin of the Fittest, p. 182. 
™ Penn. Monthly Mag., 1872; Origin of the Fittest, p. 11, 1887. 
