746 



SCIENCE 



[N. S. Vol. XXVI. No. 674 



ing to support this hypothesis of sudden 

 origin by inductive evidence the paleontol- 

 ogist is certainly at a great disadvantage 

 through deficiency of material. In order 

 to demonstrate a sudden change, a discon- 

 tinuity or a saltation in single characters, 

 one must have all or a very large number 

 of contemporary individuals for compari- 

 son. I maintain, therefore, that the paleon- 

 tologist can never demonstrate a discon- 

 tinuity, because he must always entertain 

 the suspicion that it may arise from lack 

 of evidence. The zoologist and experi- 

 mentalist, on the other hand, may demon- 

 strate a discontinuity for the reason that 

 they may have at hand large series of eon- 

 temporary individuals for comparison. 

 The paleontologist is never favored in this 

 way. 



Second, the paleontologist can never 

 prove that the appearance of a new type 

 combining a number of adaptive characters 

 is a sudden appearance, because he must 

 always admit the possibility that such a 

 tjT)e may have slowly evolved elsewhere 

 and come into the field of his observation 

 suddenly through migration. Thus I main- 

 tain that the hypothesis of Cope, Dollo and 

 Smith Woodward as to the siidden appear- 

 ance either of new adaptive characters or 

 of new types does not rest on a demon- 

 strable foundation so far as paleontology 

 is concerned. 



These criticisms, however, in no way in- 

 validate the numerous observations of these 

 and other paleontologists, among both ver- 

 tebrates and invertebrates, that new adapt- 

 ive types do suddenly come into the field 

 of observation in geological horizons and 

 mark the beginnings of rapid evolution. 



Finally, I am neither opposing nor ad- 

 vocating the so-called "mutation theory" 

 of de Vries; I simply assert that paleontol- 

 ogy is not a branch of biology in which 

 this theory can be either proved or dis- 

 proved. 



Second opinion : Hypothesis of gradual 

 appearance. So far as I know, this hypoth- 

 esis is solely paleontological in origin, and 

 is to-day chiefly maintained by certain, al- 

 though not by all, paleontologists. I re- 

 gard it as the greatest contribution which 

 paleontology has made to evolution. So 

 far as I know, the first to express it was 

 Waagen (1869). He distinguished muta- 

 tions from local or geographical variations. 

 The mutations of Waagen can only be ob- 

 served in successive geological levels, i. e., 

 at intervals of many years. They are very 

 constant, although seen in minute features, 

 and can always be recognized again. This 

 was Waagen 's original definition of muta- 

 tions as distinguished from the more con- 

 spicuous contemporary fluctuations. 



This law of Waagen received the power- 

 ful support of Neumayr (1889) and of 

 many other invertebrate paleontologists, 

 and it is receiving fuller support daily. 

 As regards the vertebrates, Osborn in 1886, 

 at the time ignorant of Waagen 's law, 

 made the same observation in the study of 

 the teeth of mammals, and termed it the 

 law of "definite variation." It has since 

 been confirmed and extended on a very 

 large scale. Thus vertebrate and inver- 

 tebrate paleontologists working entirely 

 independently of each other on wholly 

 different materials have reached similar 

 opinions. This law of gradual change in 

 the origin of single characters, measuraile 

 only at long intervals of time, rests on a 

 vast number of oiservations. 



ni. THE ADAPTIVE QUALITY OP NEW 

 CHARACTERS 



So much for the older history ot the 

 subject. 



I may now, as a paleontologist, add three 

 supplementaiy Statements as to the origin 

 of new characters by heredity which, it is 

 true, rest upon a large number of my 

 own observations, but still requires coUat- 



