314: EVOLUTION IN BIOLOGY. 



that it would account for the facts of teleology, as well 

 as for those of morphology ; and for the persistence of 

 some forms of life unchanged through long epochs of 

 time, while others undergo comparatively rapid meta- 

 morphosis. 



How far " natural selection " suffices for the produc- 

 tion of species remains to be seen. Few can doubt that, 

 if not the whole cause, it is a very important factor in 

 that operation ; and that it must play a great part in the 

 sorting out of varieties into those which are transitory 

 and those which are permanent. 



But the causes and conditions of variation have yet 

 to be thoroughly explored ; and the importance of natu- 

 ral selection will not be impaired, even if further in- 

 quiries should prove that variability is definite, and is 

 determined in certain directions rather than in others, 

 by conditions inherent in that which varies. It is quite 

 conceivable that every species tends to produce varieties 

 of a limited number and kind, and that the effect of 

 natural selection is to favour the development of some of 

 these, while it opposes the development of others along 

 their predetermined lines of modification. 



7. No truths brought to light by biological investiga- 

 tion were better calculated to inspire distrust of the dog- 

 mas intruded upon science in the name of theology, than 

 those which relate to the distribution of animals and 

 plants on the surface of the earth. Yery skilful accom- 

 modation was needful, if the limitation of sloths to 

 South America, and of the ornithorhynchus to Australia, 



