268 THEORETICAL BIOLOGY 



must get quite clear as to whether by the word " ancestor " 

 we mean only the material basis from which the new melody 

 derived its building-material, or whether we mean the new 

 melody itself. In the first case, fishes are obviously our 

 ancestors ; in the second, they are merely our relatives, 

 in so far as their melody of genesis coincides with our own. 



If we regard the increase in complexity that we see in 

 the development of each living organism, as the reflection 

 of the increase in complexity of organisms in general, we 

 arrive at an idea that is contradictory to Haeckel's biogenetic 

 principle (which requires that we have sprung from function- 

 ing, full-grown ancestors) ; we arrive at the idea that the. 

 melody of genesis that forms fishes, at a certain period in 

 certain germs ended differently, and that when this new 

 melody or rule of shaping set in, the new forms arose. 



Accordingly, we introduce an inner cause as determina- 

 tive, a cause which we do not know, and which we can do no 

 more than recognise, a sort of " further composition " accord- 

 ing to plan ; and plan we have recognised as being the creator 

 of life in general. 



In order to carry on a melody, it is not necessary to 

 introduce new notes : in the same way, it is not necessary 

 that new impulses and new genes should come in. The same 

 impulses can reach back and seize on the genes that are already 

 present, and in this way develop the melody further. We 

 may assume the impulses to be all alike, since they all display 

 the same activity, namely that of mobilising the genes ; it 

 is the genes which they affect that produce the difference. 

 It is also reasonable to suppose that the same genes arranged 

 in different sequence may give completely different results, 

 and produce new kinds of organisms. 



Admittedly, the foregoing are mere conjectures, for we 

 are without any reliable evidence. But they move in the 

 same direction as the laws with which our study of the genesis 



