Xo. 484] CLOSELY RELATED SPECIES 



213 



much knowledge of De Vries's work and apparently after a read- 

 ing of only the popular lectures published in this country/ was 

 at least thus far right, that he searched for indications of muta- 

 tion in the distribution of animals. The evidences should be 

 found even in museums, providing the museums are representative, 

 and providing mutation is a sufficient explanation of the origin of 



The Necessity of Isolation: ]Mexdeliax IxnKHiTAX( e 



Before coming to an examination of the facts as thcv an> repre- 

 sented by writers, it will be well to consider for a nioinciii a the- 

 oretical side of the subject, namely the siii>])(.s(m1 nrcrssiiii of 

 isolation as a factor in the evolutionary process, (irantiiiu that 

 new forms may appear upon the scene by Muiaiioii. wliai is to 

 become of them? How can ]\Iutation be said to oriuiiiate new 

 species — that is, stable groups — if through iiiterbreeihiiij tlie 

 mutants are at once swallowed up by the parent species with \\ hieh 

 they grow commingled V The opponents of the Miitaiioii Theory 

 hold that the isolation which the experimetiter practico in his 

 garden by means of paper bags, etc., is lackin-' in natnre and 

 that this difference between the garden and free natnre vitiates 

 the exi)erinuMits. 



(h'senssed in the writings of Romanes and (inl'iek: the hilter has 



from the theoretical standpoint and upon the ha>is ot" the very 

 limited knowledge of heredity of a few years ai^o. The eon( lu- 

 sion of these authors i.s that some kind of M-r(-i:ati..n or iM.hnion 

 is necessary for the ^necess of a new race. W hih- W a-iier 's!)) 



