DARWIN'S ORIGIN OF SPECIES 231 



considered the matter, and decided that, in his opinion, evolution 

 did not proceed in Nature by such means. Professor De Vries' 

 statement that Darmn beUeved evolution occiuTed both by 

 mutations and by the accumulation of fluctuating variations, is 

 traversed by Professor Poulton. If we read him rightly, his 

 attitude is that Dar-^dn denied altogether the probabiUty of 

 evolution in Nature by mutation. It is certain that in some of 

 his letters, Darwin has on more than one occasion expressed, what 

 was for him, very decided opinions adverse to modifications of 

 species by sudden jumps. But it is only fair to bear in mind, 

 that Darwin himself said " that no definition can be draM'n 

 between monstrosities and sUght variations (such as his theory 

 requires) though he suspected there was some distinction." 

 That was in the year 1860. In 1873 he said, '' It is very difficult 

 or impossible to define what is meant by a large variation. Such 

 graduate into monstrosities." We cannot, therefore, very clearly 

 see the real justification for believing that evolution can proceed 

 by slight variations and yet not by larger ones or monstrosities, 

 when no definition which can express real difierences between 

 them can be framed. Here, in fact, Darwin was face to face 

 with the difficulty which faces us to-day. Are these small 

 variations — the so-called fluctuating variations — in reality, in 

 some cases at any rate, simply small mutations ? That is, variations 

 which really express definite features due to gametic factors and 

 which are capable of hereditary transmission. And, further, is it 

 possible that under the one term, namely, " fluctuating varia- 

 tions," we have been all along including two externally similar 

 but intrinsically different phenomena ? Are some of these 

 variations really small mutations and the others merely individual 

 responses of a plastic organisation to differences in environmental 

 influences ? Professor Poulton becomes satirical upon this 

 point, and in alluding to the fact that the Mendelian has recognised 

 the possibility that some small variations are in reality mutations 

 of small moment, has twitted them with the hope that they 

 may yet " save their face " by calHng the same thing (Darwin's 

 small variations) by another name (small mutations). But this 

 mode of controversy is a double-edged sword. For suppose the 

 future shall demonstrate that there are two kinds of small varia- 

 tions ; those which are germinal and those which are environ- 

 mental. The latter are not inherited, the former are. We must 

 distinguish between them. For is it not the function of science 

 to analyse ? The difference between the Present and the Past 

 in our conception of these things is that now we are beginning to 

 perceive the possibility that there are two kinds of fluctuating 

 (small) variations and propose to distinguish them in our minds 

 by calling them different names. Is that scientific or not ? At 



