xvin ORGANISATION AND EVOLUTION 417 



this stage it is clear that the unity of the nervous 

 system is not the unity with which we are familiar 

 in man, or in animals which approach man in the general 

 plan of their structure. In truth, unity of nervous 

 organisation is less necessary and perhaps less possible 

 where behaviour consists mainly of a series of instinctive 

 reactions. Reflexes and instincts may be efficiently carried 

 out, each by its own appropriate mechanism, and their 

 mutual dependence may be slight. But in proportion as 

 the organism comes to rely upon its own experience for 

 guidance, it becomes more and more necessary that 

 different actions and different experiences should be 

 brought to bear upon one another ; and for this purpose 

 different parts of the nervous system must be more 

 intimately correlated. Thus completeness of physical 

 unification serves as a condition of that still higher 

 organisation of life which is the work of intelligence. 



In the same way, social life has its ultimate basis in a 

 refinement of physical organisation whereby the play of 

 separate individual lives becomes interwoven. This is first 

 seen at a low stage of the animal world in the distinction 

 of sex whereby each individual becomes an incomplete 

 organism, needing union with another to fulfil its vital 

 functions, and endowed accordingly with means of finding 

 and uniting with the other. It is seen, secondly, in the 

 physical relation of mother and young both before and 

 after birth a relation which, as has been shown, steadily 

 grows in importance as we ascend the orthogenic scale. 

 In both cases physical bonds unite otherwise distinct 

 individuals l to form temporarily or permanently a higher 

 organisation. As intelligence in general starts from the 

 organised unity of the individual, so the social intelligence 

 the organising principle which makes a unity of separate 

 individual lives starts with a physical organisation which 

 does the same work in little. 



Thus from first to last the essence of orthogenic 

 evolution is a progress in Organisation. Such a progress 



1 In the case of the embryo indeed we get a doubt as to the dis- 

 tinctness of individuality quite parallel to that which we have noted in 

 regard to the component parts of the lowest Metazoa. 



E E 



