264 A Review of the Modern Doctrine of Evolution. | April, 
climate, escaping enemies, and reproducing their kind. The 
struggles of animals have been on this platform, and mind has 
only been necessary to aid in accomplishing the ends above 
mentioned. Wonderfully effective machines for grinding, cutting, 
seizing and digging; for running, swimming and flying have been 
produced. The development of mind proper must appear in the 
size and structure of the brain; and though the history of the lat- 
ter in past ages must always remain, in large part, hidden from us, 
it is known that in the former respect there has ‘been great progress 
made in various lines of animals. Now the line which has car- 
ried brain to its present development in man, the Quadrumana, 
has been deficient in special mechanical excellencies of the kind 
enumerated above. Perhaps primitive inferiority in these many 
respects has kept the Quadrumana under greater mental tension, 
and compelled them to exercise caution in their acts and give that 
opportunity to thought which was less demanded in the case of 
other animals. Furthermore, if they are less specialized in their 
mechanism than most other Mammalia, they are less restricted 
by it to peculiar modes of life. They are more versatile, and 
more capable of the adoption of new habits as a consequence. 
And here we have a glimpse of a most important principle in 
evolution, which is the keynote to its method; this is what 
have called Tke Doctrine of the Unspecialized. 
Paleontology shows that the succession of living types has not 
been ina single straight line. It has been in many divergent 
lines, and a large number of them have not continued to the 
present time. The history of life has been well compared to a 
tree with divergent branches, many of which do not reach the 
elevation of the summit. Furthermore, in the many cases in 
which we can trace the lower lines to the present period, it is 
evident that in their present condition they could not have given 
rise to the higher forms. Each line, in fact, has developed to an 
extreme of specialization of structure, which it would seem is 
incapable of modification in any direction very divergent from 
that which it has already taken. Much less have such special- 
ized types been able to survive the environment for which they 
were designed; with important changes in that respect they have 
perished. A few examples will serve to illustrate my meaning. 
The direction of development has been from fishes, through , 
Batrachia and reptiles, to birds and mammals. But we cannot 
