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THE AMERICAN NATURALIST 



[Vol. XLVI 



other characters. Such unit characters may in them- 

 selves be extremely complex and include the possibility 

 of further splitting up." The point where Mendelism 

 bears on the problem is, therefore, the continuous or dis- 

 continuous origin of the thousands of characters which 

 display this more or less complete discontinuity in hered- 

 ity. 



I. Evidences for Discontinuity 

 Darwin has been widely misunderstood of late as be- 

 lieving in continuity, 3 whereas he chiefly believed in dis- 

 continuity. 4 In his original (1859) and final (1872) 

 opinion evolution is due chiefly to the selection of herit- 

 able ''individual differences"; these have been under- 

 stood by some as "fluctuations." His true meaning as 

 to these individual differences is to be found in the cases 

 he cited, which may be collected from hundreds of ob- 

 servations in the "Origin of Species" and "Variation 

 of Animals and Plants under Domestication," to the 

 effect that such individual differences or neiv characters 

 were in the nature of minor saltations, structural or 

 functional, and always hereditary. If we note some of 

 the observations which he assembled in commenting on 

 the genesis of the race horse and the grayhound, breeds 

 which he used by way of illustration of the genesis of 

 new forms in nature, we find they include such suddenly 

 appearing new characters as horn rudiments, tailless- 

 ness, curliness of the hair, characters which are discon- 

 tinuous in Bateson's sense, or mutations in that of De 

 Vries ; 5 intermingled with these new characters he cited 



