SUMMARY OF THE EVIDENCE. - 2O/ 



held that there have been several starting-points of 

 origin instead of one, but this view is not called for 

 by the facts, and is really of no value. 



While the various lines of investigation which we 

 have considered indicate strongly the fact of genetic 

 descent, it is evident that thus far we have seen no 

 indication of the manner in which this evolution has 

 been manifested. It is consistent with the evidence 

 we have considered to believe that the evolution of 

 species has always been, as it seems to be to-day, an 

 exceedingly slow process ; that individual varia- 

 tions have gradually given rise to varieties, and 

 these have slowly become species, each species thus 

 taking thousands of years in its formation. But it 

 is also consistent with the evidence to believe that 

 there have been periods of rapid advance and modi- 

 fication, alternated with periods of comparative rest; 

 the present time being one of the latter. It is pos- 

 sible that species have always been evolved by an 

 infinite number of minute steps, so that the whole 

 may be looked at as a .continued growth ; or, it is 

 possible that there may have been some abrupt ad- 

 vances, by variations of considerable amount taking 

 place in a single generation ; or, it is even possible 

 that these jumps may have been great enough to 

 originate a new species at a single birth. It is pos- 

 sible that evolution may have been from the first a 

 continued advance, or there may have been at times 

 an advance, at times a pause,' and at times a retro- 

 gression. All of these conceptions are logical, and 

 each has been and is held to-day by various natural- 

 ists, as expressing in their opinion the nearest ap- 



