EVOLUTION AS A NATURAL PROCESS 107 



subject for the first time find it difncult to haiiish 

 from their minds the idea that evohition, even if it ever 

 took place, has been ended. Tliey tiiink it futile to 

 expect that a scrutiny of to-day's order can j)()ssibly 

 find influences powerful enough to have any share in 

 the marvelous process of past evolution demonstrated 

 by science. The naturalists of a century a^o held a 

 similar opinion regarding the earth, vic^wing it a,s an 

 immutable and unchanged product of sui)ernatural 

 creation, until Lyell led them to see that tlie world is 

 a plastic mass slowly altering in countless ways, h 

 is no more true that living things have ceased to evolve 

 than that mountains and rivers and glaciers are fixed 

 in their final forms ; they may seem everlasting and 

 permanent only because a human life is so brief in 

 comparison with their full histories. Like the develoj)- 

 ment of a continent as science describes it. tlu^ origin 

 of a new species by evolution, its rise, culmination, 

 and final extinction may demand thousands of years; 

 so that an onlooker who is himself only a conscious 

 atom of the turbulent stream of evolving organic life 

 does not live long enough to observe more than a small 

 fraction of the whole process. Therefore living species 

 seem unchanged and unchangeable until a conviction 

 that evolution is true, and a knowledge of the metlind 

 of science by which this conviction is borne upon one, 

 guide the student onwards in the further searcli for 

 the efficient causes of the process. 



The biologist employs the identical methods used 

 by the geologist in working out the past history of 

 the earth's crust. The latter observ(\s the forces at 

 work to-day, and compares the new layers of rock 



