398 CONCLUSION 



divergent lines of development ; though the converse is 

 by no means true only a few specific differences 

 actually lead to wide divergence in subsequent evolution. 

 We are still very ignorant as to the causes of the first 

 appearance of such small differences. From the point 

 of view of their effects they are chance occurrences. 



We have seen that the activities of living substance 

 which are common to all organisms the vital functions 

 are functions of the particular, the unique physico- 

 chemical complex which we call protoplasm, and that 

 we can partly explain how these functions or activities 

 result from the physico-chemical structure. We have 

 also seen reason to believe that the great primary 

 differentiation between animals and plants arose from 

 small differences in the protoplasm of different primitive 

 organisms, and that similar differences exist now 

 between closely allied species. There is evidence that 

 such differences are still frequently occurring between 

 different individuals or groups of individuals of the 

 same species, and that in this way new species originate. 

 In the higher forms of life, animals and plants with 

 complicated bodies of definite structure, such slight 

 changes in the chemical composition of the protoplasm 

 may be expressed in various definite ways, in slight 

 but definite alterations in the form and structure, or 

 in the colour, of the body or of particular parts of the 

 body, such as we know is actually characteristic of the 

 differences between species. In some cases such 

 changes, leading to the origin of new species, can be 

 shown with fair probability to be the result of the 

 effect of some change in the surroundings, for instance 

 increased dryness or wetness, or the presence of some 

 chemical substance which is absorbed by the body. 

 But in the greater number they are probably the result 



