2 1 6 E VOL UTION OF TO-DA Y. 



length of this time in years, it is evident enough that 

 it has been sufficient to develop the present species, 

 from the simple fact that they have developed in 

 this time. This matter of time is no difficulty for 

 evolution, but it does raise an objection to that form 

 of evolution which evolves species by the slow pro- 

 cess of selection of minute variations. If change has 

 been more rapid in the past than at present, or if 

 the modifications have taken place by periods of 

 rapid advance, alternating with those of comparative 

 rest, there is no trouble at this point ; but if the 

 slow change which has taken place since the glacial 

 period is taken as a criterion, the 300,000,000 years 

 of Darwin do not appear to be a great demand ; and 

 if natural selection has had only such minute varia- 

 tions to work with as the theory assumes, the time 

 of the geological ages appears too short. 



Not only has this development of species been 

 very slow, but it must also have been very gradual. 

 Our present species have, according to this theory, 

 descended from the older forms by slow selection of 

 minute variations, which have always been in danger 

 of disappearing by crossing. There have been no 

 abrupt changes. New species have not arisen by 

 the crossing of two other species, but all have arisen 

 by the slow process of minute changes. It follows 

 from this that every species has been connected with 

 its predecessor by a very great number of intermedi- 

 ate links, each varying only slightly from the forms 

 before and after it. If we could get a comprehen- 

 sive view of the animals in the past and present, we 

 would find no two species radically distinct, but all 



