The Descent of Man. 165 



suggests that life began independently at each pole, and 

 thence spread to other portions of the earth. Future investi- 

 gations in the Argentine Kepublic are likely to throw much 

 light on this theory, which cannot yet be said to be es- 

 tablished as regards vertebrate animals. 



Following the line of descent, we hncl that many lines of 

 progress have maintained themselves, and that these lines 

 are not accidental or arbitrary. Here and there, indeed, we 

 find that some magnificent capabilities have been switched 

 off the track ; and for these progress has ceased. In other 

 cases retrogression has taken place. A profound lesson 

 may be drawn from the observation of this fact. We may 

 be thankful that our ancestors got on the right track ; and 

 if we did come from a humble origin we can rejoice in what 

 we have attained, and reflect upon what we may escape in 

 the future. 



The origin of variations can be traced to varied causes, 

 and modifications are almost always explainable by careful 

 study. The object of all things is to live ; and to secure 

 the means of living is the end which they aim to accomplish. 

 The motion consequent upon this effort is the active, and 

 the environment the passive factor in development. One 

 of the first principles in progress is the capacity to move 

 from place to place. Those animals which become sessile, 

 or fixed to one spot, cease to progress, and tend rapidly to 

 retrograde. The structural changes are induced by contact 

 with environing conditions, and by motion. There is pro- 

 gressive evolution, and also retrogressive evolution ; progress 

 and degeneration. The competition of the struggle for 

 existence compels excellence. The absence of it tends to 

 inactivity and degeneracy. Groups have thus arisen, and 

 then fallen. The result on the whole has been a constant 

 advance since the beginnings of life on the earth ; but the 

 number of degenerate lines is nevertheless very great. 



The Lamarckian view that structure results from use is 

 undoubtedly correct. In this way certain mechanical causes 

 have induced changes in the skeletons and teeth of verte- 

 brate animals. These hard parts determine the character 

 of the entire organism, the softer portions conforming to 

 them and being modified in the directions which their changes 

 indicate. The original impulse is in the activity of the ani- 

 mal. If all animals had been created alike they would at 

 •once have begun to act differently, and modifications would 



