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, eg. the 
muscles of the calf and buttocks attained a massive development. 
Such examples might be multiphed, but the above will suffice 
to show that these modifications are not mere freaks of chance, 
mere lusus nature, 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 
