52 Proceedings of Indiana Academy of Science. 
definite pattern. Even embryo man is not ashamed of his ancestors, although 
some adult men are. If this condition dominates both adult and embryonic 
life, the species may continue indefinitely without change, like the brachi- 
opod Lingula, the same today as in Cambrian time. Differentiation on the 
other hand, creates new species. and thus forms the basis of progressive 
evolution. Continuous repetition of the process through long periods of time 
has given rise to all the higher animals and plants. In the great majority of 
organisms, however, progress has been slow, and in many cases, has ceased 
altogether. Of the vast number of species that now live, or have lived, on 
the earth, only a few have found the path leading to high rank. 
These differences in the capacity of organisms for progressive evolution 
may be explained in a way by saying that certain types are more plastic 
than other’. Some are easily moulded into new shapes, while others change 
slowly or not at all. When such a species reaches the limit of differentia- 
tion permitted by its organizatien, it may continue to exist cn the same 
plane, but it can not advance. According to Herrick, the evolution of the 
whole group of arthopods has been definitely limited by the lack of plasticity 
of the ladder type of neryous system, which apparently reached its highest 
development in cretaceous insects about two million years ago. At the same 
time also were established those rigid instincts which have continued with- 
out change down to the present. The more plastic tubular nervous system 
of the vertebrates, on the other hand, has shown itself capable of enor- 
mous development, and has provided the nervous equipment of those ani- 
mals in which inherited instincts are largely controlled by in‘elligence. 
With a neryous system constructed on the tubular plan, the mammals have 
advanced farther than other animals, but among these only the primates 
reached the highest grade of development. From this group finally came 
man. 
With the advent of man the old laws of evolution continue to operate, 
but they are more or less under the control of intelligence, which becomes 
a factor of increasing importance. As men were drawn together for pro- 
tection or otherwise, societies were formed and division of labor occurred, 
but no physical differences appeared, such as are found in other animal 
societies, and thus each individual man retained the capacity to do all 
kinds of work. In such societies were laid the foundations for those col- 
lective activities, such as language, literature, science and government, 
which go to make up civilization. Henceforth each generation receives not 
only the heritage of the germ cells but also a heritage of knowledge accumu- 
lated by previous generations. By virtue of man’s superior mental capacity, 
each generation appropriates the inherited wisdom, adds its own contribu- 
tion to the general store and transmits the whole to its successor. In this 
manner the social heritage is enlarged. 
Continuous operation of the general laws of evolution in human history 
is indicated by the appearance of different types and races of men, the 
inhabitants of different regions showing different characteristics, as in the 
case of lower organisms. As population and division of labor increased, 
more or less permanent conditions developed, but many of the early societies 
have doubtless disappeared without leaving a trace of their existence, 
while others are known only by implements or other remains. Among the 
surviving peoples all grades of culture are rep:e ented. many having ceased 
