July 28, 1905.] 



SCIENCE. 



Ill 



dominion of the earth, which the decadent 

 dinosaurs had departed from. They came 

 in a great diversity of forms, and their 

 organization was little if any inferior in 

 rank to that of the mammals now living 

 of lower grade than the qiiadrnmana. 

 There has been found no evidence of their 

 evolution from earlier forms by any slow 

 process, not even from the previously exist- 

 ing non-plaeental mammals; and their spe- 

 cies all became extinct at, or before, the 

 close of the Eocene epoch. They were then 

 replaced by the Miocene and Pliocene mam- 

 malia respectively, each fauna containing 

 many strange and suddenly introduced 

 forms, and each losing largely by extinc- 

 tion. Indeed, the history of the mammalia 

 from the earliest Tertiary to the present 

 time embraces a record of the rapid and 

 varied evolution of the highest grades of 

 animals, culminating in man. If it should 

 ever be possible to trace the evolution of 

 man from the lower animals it will doubt- 

 less be found that it has been accomplished, 

 not by the slow process of natural selection, 

 but by a series of sudden mutations. 



In the foregoing remarks the terms rapid 

 and sudden, referring to the introduction 

 and extinction of the larger divisions of 

 faunas and floras, are sometimes used in a 

 comparative sense, and sometimes literally. 

 The latter use of those terms, however, is 

 more especially made when referring to 

 species. If the introduction of families, 

 orders and classes, and even of entire 

 faunas and floras, was so effected as to 

 give the appearance of suddenness, or even 

 of rapidity, it necessarily follows that spe- 

 cies, which are the recognized component 

 units of those greater groups, were pro- 

 duced with actual suddenness. 



The necessity for assuming the sudden 

 origin of species being apparent, the first 

 question that naturally arises is that of 

 the manner of their origination. This must 



have been accomplished either by special 

 creation, as w^as formerly believed, or by 

 some natural genetic process of transfor- 

 mation. The time seems to have passed 

 for giving any consideration to the former 

 proposition, and it only remains to consider 

 some natural theory. While many expres- 

 sions of belief have from time to time been 

 made that species have originated suddenly 

 by some natural process, the only clearly 

 defined theory of this kind is the one pro- 

 posed by Professor de Vries, of Amster- 

 dam, under the name of the mutation 

 theory.* It is essentially as follows : 



Species originate from other species 

 through the ordinary function of reproduc- 

 tion, but they each originate suddenly and 

 completely by one mutative act, and not by 

 the slow cumulative variation of individu- 

 als. The beginning of the mutative process, 

 which is due to some at present unknown 

 natural determinate cause, is a rearrange- 

 ment of the groups of component molecules 

 of the protoplasmic contents of the germ 

 cell. It occurs when the' ovule containing 

 that cell has, by the natural process of re- 

 production, been fertilized and is about to 

 give origin to a new individual. If that 

 molecular change occurs, the new indi- 

 vidual thereby acquires changed structural 

 characters and becomes an original repre- 

 sentative of a new species. If no such 

 molecular change occurs in the germ cell of 

 a fertilized ovule, which is usually the case, 

 the result is only that of ordinary repro- 

 duction. The new species thus produced 

 by mutation is in immediate possession of 

 clearly distinguishing and heritably trans- 

 missible characters; and it has no more 

 tendency to hybridize with any member of 

 the mother species than have other species. 

 The characteristics and perpetuation of the 

 mother species are in no way affected by 



* ' Die Mutationstlieorie,' von Hugo de Vries, 

 Vols. ] and 2, Leipzig, 1901, 1902. 



