52 Proceedings of Indiatm Academy of ^Science. 



defiiiito pattern. Even embryo man is not ashamed of his ancestors, although 

 some adult men are. If this condition dominates both adult and eml»ryonic 

 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 liave found the path leading to high ranlv. 



These diftei-ences in the caiKicify of organisms for progressive evolution 

 may be explained in n way by sayin-i that certain types are moi'e plastic 

 than other-. Some are easily moulded into new shapes, while others clumge 

 slowly (u- not at all. When such a species reaches the limit of dirt'erentia- 

 tion permitted by its organizaticn, it may continue to exist cu 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 nervous 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 intelligence. 

 With a nervous 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 api^eared. 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, 

 whicli 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, 

 eacli 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 oidy by implements or otluM- remains. Among the 

 surviving peoples all grades of culture are re)iie ented. many luiving ceased 



