CONCLUDING REMARKS 213 



parts which had become superfluous would have been in the way 

 of other active parts, and would have hindered their development. 

 Indeed, had all parts which the ancestors possessed been necessarily 

 retained, an abnormal animal would at last have been produced 

 a monster no longer capable of living. The degeneration of 

 parts which have become superfluous is thus a condition of 

 progress." 



But what is it that actually initiates these various changes ? 

 What is their first cause ? This question cannot be answered off- 

 hand on account of the great number of circumstances which 

 have to be taken into account. First, we have to consider 

 external influences of the most varied kinds which affect the 

 different organs, or systems of organs, in a progressive or 

 retrogressive manner, leading to new acquisitions or to gradual 

 losses. These changes, however, have, as it were, to be intro- 

 duced by the occurrence of slight variations, and then (if I may 

 use a military term) when once a breach has been made in any 

 part, a point of least resistance is formed for pathological affec- 

 tions, as I have tried to prove in the foregoing pages, and a 

 substitute for the gradually degenerating organs has to be found. 

 In other words, as soon as a transformation takes place in any 

 part of the body, correlative alterations in some other part 

 commence, so that, as it were, a wave of modification passes from 

 one system of organs to another. For example, when the 

 dentition of our ancestors degenerated, and the canines became 

 reduced, the important weapons of attack and defence thus lost 

 had to be replaced, if the struggle for existence was to be 

 advantageously maintained. Concurrently with the reduction of 

 powerful jaws the brain was developing, and the intelligence 

 attained a sufficiently high degree of perfection to invent 

 weapons, at first no doubt of a very simple character. Or 

 again, as the foot gradually changed from a seizing organ into 

 one for support of the body, and its musculature consequently 

 changed, then, in adaptation to the new function, great 

 alterations had to be effected not only in the skeleton of the 

 limb, but also in its muscular and nervous system, e.g. the 

 muscles of the calf and buttocks attained a massive development. 

 Such examples might be multiplied, but the above will suffice 

 to show that these modifications are not mere freaks of chance, 

 mere lusus natures, but are the expression of law - abiding 

 processes, even if we cannot always succeed in determining their 

 first cause. At all events, these processes need immense periods 



