INFLUENCE OF ENVIRONMENT 107 



Before setting forth to examine the proofs of this fact, which deserves 

 our attention and is so important for zoological philosophy, let us 

 sum up the thread of the discussions that we have already begun. 



In the preceding chapter we saw that it is now an unquestionable 

 fact that on passing along the animal scale in the opposite direction 

 from that of nature, we discover the existence, in the groups composing 

 this scale, of a continuous but irregular degradation in the organisa- 

 tion of animals, an increasing simplification in their organisation, 

 and, lastly, a corresponding diminution in the number of their 

 faculties. 



This well-ascertained fact may throw the strongest light over the 

 actual order followed by nature in the production of all the animals 

 that she has brought into existence, but it does not show us why the 

 increasing complexity of the organisation of animals from the most 

 imperfect to the most perfect exhibits only an irregular gradation, in 

 the course of which there occur numerous anomalies or deviations 

 with a variety in which no order is apparent. 



Now on seeking the reason of this strange irregularity in the increas- 

 ing complexity of animal organisation, if we consider the influence 

 that is exerted by the infinitely varied environments of all parts of the 

 world on the general shape, structure and even organisation of these 

 animals, all will then be clearly explained. 



It will in fact become clear that the state in which we find any animal, 

 is, on the one hand, the result of the increasing complexity of organisa- 

 tion tending to form a regular gradation ; and, on the other hand, 

 of the influence of a multitude of very various conditions ever tending 

 to destroy the regularity in the gradation of the increasing complexity 

 of organisation. 



I must now explain what I mean by this statement : the environment 

 affects the shape and organisation of animals, that is to say that when the 

 environment becomes very different, it produces in course of time 

 corresponding modifications in the shape and organisation of animals. 



It is true if this statement were to be taken literally, I should be 

 convicted of an error ; for, whatever the environment may do, it 

 does not work any direct modification whatever in the shape and 

 organisation of animals. 



But great alterations in the environment of animals lead to great 

 alterations in their needs, and these alterations in their needs neces- 

 sarily lead to others in their activities. Now if the new needs become 

 permanent, the animals then adopt new habits which last as long 

 as the needs that evoked them. This is easy to demonstrate, and 

 indeed requires no amphfication. 



It is then obvious that a great and permanent alteration in the 



