Febeuaey 1G, 1906.] 



SCIENCE. 



243 



that they can— how does it follow that 

 'then in truth Darwinism can afford to lose 

 the individual variations as a basis.' Is 

 not this a case of enthusiasm run wild ? Is 

 it not like arguing that if it can be proved 

 that a man ate meat for breakfast, then of 

 course he could not have eaten bread ! To 

 my mind the striking fallacy of de Vries's 

 argument is his assumption that because it 

 can be shown that sports occur in nature, 

 and that in rare cases species arise there- 

 from, then the theory that species are pro- 

 duced by the progressive development of 

 slight individiial variations must be 

 abandoned. Why can not species origi- 

 nate in both ways? The occurrence of 

 sports among animals and plants being 

 admitted, the question arises as to what 

 becomes of them. According to Darwin, 

 Weismann, Dall, Jordan and a host of 

 others they are lost by the swamping effects 

 of interbreeding. That this is the usual 

 result in both plants and animals I think 

 every one will admit, for even de Vries 

 frankly states that their perpetuation in 

 giving rise to new species is so exceedingly 

 rare that he is able to cite only a single 

 authenticated case. I do not assume to 

 be a botanist ; nevertheless, for more than 

 a quarter of a century I have been an 

 earnest field student of plants in their rela- 

 tions to geographic environment. These 

 studies have convinced me that with plants, 

 as with animals, the usual way in which 

 new forms (subsJDeeies and species) are 

 produced is by the gradual progressive 

 development of minute variations. 



But we are not now concerned with 

 plants. The question before us is, 'Do 

 species among the higher vertebrates origi- 

 nate by the sudden acquirement of new 

 characters?' In seeking an answer I have 

 passed in review more than a thousand 

 species and subspecies of North American 

 mammals and birds without finding a single 

 one which appears to have originated in 



this way. Among the higher vertebrates, 

 therefore, the conclusion seems justified 

 that if species ever originate from sports, 

 such mode of origin must be exceedingly 

 rare. My own conviction is that the origin 

 of species by mutation among both animals 

 and plants is so uncommon that as a factor 

 in evolution it may be regarded as trivial. 



If species do not ordinarily originate in 

 this way, it is fair to ask, 'How do they 

 originate?' My answer is, 'By the slow 

 but progressive acquirement of characters 

 that have their beginning in minute varia- 

 tions. ' 



It is hardly necessary in the present con- 

 nection to review the theories concerning 

 the inception of variation, for whether or 

 not we believe in the potency of dynamic 

 influences, we all admit that individual 

 organisms vary, and most of us are agreed 

 that in the struggle for existence the bene- 

 ficial variations are likely to be preserved^ 

 the harmful ones eliminated, by the action 

 of natural selection. Some of us go fur- 

 ther and believe that the universal and 

 irrepressible tendency of organisms to vary 

 results in the perpetuation, not only of 

 distinctly iiseful departures, but sometimes 

 also of those which, though not harmful, 

 seem to be of not the slightest service to 

 either the individual or the species. These, 

 according to Dr. David Starr Jordan, owe 

 their inception to geogTaphic isolation. Dr. 

 Jordan states: "The adaptive characters 

 a species may present are due to natural 

 selection or are developed in connection 

 with the demands of competition. The 

 characters, non-adaptive, which chiefly dis- 

 tinguish species, do not result from natural 

 selection, but from some form of geograph- 

 ical isolation and the segregation of indi- 

 viduals resulting from it. * * * Adapta- 

 tion is the work of natural selection; the 

 division of forms into species is the result 

 of existence under new and diverse condi- 

 tions." Jordan's view is that 'the char- 



