ON THE ORIGIN OF SPECIES. 45 



counted for as easily by accepting exceedingly slow changes as the 

 causes of the formation of species, as they would be were we to con- 

 sider them due to shocks occurring but once in a protracted period. 

 Darwin fully realized this and considered the doubt upon this subject 

 as one of the weakest points of his theory. 



Darwin, as did many since, compared the origin of species in 

 nature to the methods, ordinarily used in agriculture, to obtain im- 

 proved races of plants and animals. On this subject much confusion 

 exists. Horses, for instance, are improved principally by crossing with 

 specimens of a superior race, which specimens more or less fully trans- 

 fer the good qualities of the race to the descendants. But it is certain 

 that in nature the species did not originate in this manner, at least 

 not as a general rule. Improved races are obtained only by careful 

 and constant selection in one direction. This bears a great resemblance 

 to the origin of species, but there is this objection, that such a race 

 would never be independent of selection; as soon as selection ceases, 

 the good qualities disappear. Species and subspecies, even true varie- 

 ties, on the other hand, are totally independent of the mother species ; 

 neither in nature nor in cultivation do they return to the old type, 

 either by a change in environmental conditions or by the cessation of 

 a selection; always provided of course, that accidental crossing is 

 impossible. 



The experience yielded by agriculture would lead one to consider 

 a gradual transition from one species into another improbable. They 

 point to a distinct difference between gradually improved races and 

 those suddenly formed, so-called varieties. The former bear no resem- 

 blance, the others a resemblance in all respects to wild species. 



During the last few decades several writers have expressed them- 

 selves more or less strongly against the conception of a gradual origin 

 of species. In America Cope was the one to set the example. Among 

 paleontologists Dollo, among zoologists Bateson, and recently among 

 botanists Korschinsky declared themselves in favor of the doctrine of 

 the discontinuity of the natural ancestral trees. But their opinions 

 have not been sharply defined and formulated and are based upon an 

 acquaintance with facts not much larger than that commanded by Dar- 

 win himself. Hence their small influence and the small progress 

 made by their convictions. Hence the American paleontologist Scott, 

 a devoted adherent of Cope's doctrine, deemed it necessary to defend 

 this doctrine against Bateson 's book. For his conception of discon- 

 tinuity is entirely different from that of Bateson. They are both dis- 

 satisfied with the reigning views on the origin of species by gradual 

 variability, but in its place each wishes to put an entirely different con- 

 ception. 



