DISCONTINUITY BETWEEN SPECIES 73 



species and varieties are produced from existing forms by 

 sudden leaps." ] 



This statement seems to assume that " species " are indi- 

 vidual groups of animals or plants always distinct and rarely 

 or never merging into each other. This assumption appears 

 to be very generally made by the followers of Bateson. 

 Thus R. H. Lock writes : " The species riddle presents itself 

 definitely as the problem of the existence of a series of dis- 

 continuous groups of creatures, sharply marked off the one 

 from the other." And again: " Species arise by mutation, by 

 a sudden step in which either a single character or a whole 

 set of characters together become changed." 2 Bateson writes: 

 " We see all organised nature arranged in a discontinuous 

 series of groups differing from each other by differences 

 which are specific." 3 J. A. Thomson writes : " But to think 

 of new species arising by slow changes of this sort is in many 

 ways difficult, apart altogether from the fact that definite 

 demonstration of the operation of selection has rarely been 

 attempted." 4 "Now there is no need to hamper the evolu- 

 tion theory by restricting selection to minute variations. 

 We know that sports, mutations, or discontinuous variations 

 are frequent, and that they are remarkably stable in their 

 hereditary transmission." 5 (This may be, but we know of 

 the stability of variations, large and small, only under arti- 

 ficial conditions.) 



Now, those biologists who have been largely occupied in 

 the study of species and varieties find that their work of 

 classification is often rendered almost hopeless by the way 

 that the so-called species merge into each other. The 

 following quotation expresses this feeling very strongly : " It 

 is the discontinuity which strikes Bateson and those who 



1 De Vries, H. , Species and Varieties, their Origin by Mutation, Chicago and 

 London, 1905. 



2 Recent Progress in the Study of Variation, Heredity, and Evolution, pp. 11 

 and 144, London, John Murray, 1906. 



3 Materials for the Study of Variation, p. 17, London, 1894. 



4 Heredity, p. 80, London, 1908. 

 8 Op. cit., p. 81. 



