AuvGustT 13, 1897. ] 
“Of these doctrines it may be observed that the first 
and second are now the common property of evolu- 
tionists, and are recognized everywhere as matter of 
fact. The names which I selected to express them 
have, however, only come into partial use. The 
author believes that, although the doctrine was 
vaguely shadowed out in the minds of students prior 
to the publication of this essay, it had not previously 
been clearly expressed, nor been reduced to a demon- 
stration. Of the truth of the doctrine the author is 
more than ever convinced, and he believes that pale- 
ontological discovery has demonstrated it in many in- 
stances, and that other demonstrations will follow. 
The fourth proposition (that of homologous groups) 
is now held as a hypothesis explaining the phylogeny 
of various groups of animals. For the descent of one 
homologous group from another, the term polyphyletic 
has been coined. It remains to be seen whether the 
doctrine is of universal application or not. That ho- 
mologous groups belong to different geological hori- 
zons, as stated under the fifth head, has been fre- 
quently demonstrated since the publication of the es- 
say. That the sixth proposition is true in a certain 
number of cases is well known, and it follows that 
the seventh proposition is also true in those cases. 
The latter hypothesis, which was originally advanced 
by Professor Agassiz, is, however, only partially true, 
and the advance of paleontological study has not dem- 
onstrated that it has had a very wide application in 
geological time. 
“A proposition which was made prominent in this 
essay was that the prevalence of non-adaptive charac- 
ters in animals proves the inadequacy of hypotheses 
which ascribe the survival of types to their superior 
adaptation to their environment. Numerous facts of 
this kind undoubtedly indicate little or no activity 
of aselective agency in nature, and do point to the 
existence of an especial developmental force acting by 
a direct influence on growth. The action of this force 
is the acceleration and retardation appealed to in this 
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 ac- 
counts 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 characters 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 ‘comple- 
mentary location of growth-force.’ ”” 
We can only consider the ‘law of accel- 
SCIENCE. 
239 
eration and retardation.’ 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 repe- 
titions; and grade influence merely determined the 
number and location of such repetitions. 
*h. Acceleration signifies addition to the number 
and location of such repetitions during the period 
preceding maturity, as compared with the preceding 
generation, and retardation signifiesa reduction of the 
number of such repetitions during the same time.* 
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 anato- 
mists, that man and monkeys belong to the same order 
of Mammalia, and differ in those minor characters, 
generally used to define a ‘family ’ in zoology. 
‘* Now, these differences areas follows: In man we 
have the large head with prominent forehead and 
short jaws ; short canine teeth without interruption 
behind (above) ; short arms, and thumb of hand not 
opposable. In monkeys we have the reverse of all 
these characters. But what do we see in young 
monkeys? A head and brain as large relatively 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. * * * At this 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. * * * 
‘* Now in the light of various cases observed, where 
members of the same species or brood are found at 
adult age to differ in the number of immature charac- 
ters they possess, we may conclude that man origi- 
nated in the following way : that is, by a delay or 
retardation of growth of the body and fore limbs as 
compared with the head ; retardation of the jaws as 
compared with the brain case, and retardation in the 
protrusion of the canine teeth.”’ 
There is good reason for thinking that 
fallacy is involved in this argument and 
that quite a different interpretation should 
be put on the evolution of the characters in 
*Proc. Am. Phil. Soc., 1871; Origin of Fittest, p. 
182. 
fPenn. Monthly Mag., 1872; Origin of the Fittest, 
p. 11, 1887. 
