Februakt 11, 1921] 



SCIENCE 



131 



large steps; while these may occur, minute herit- 

 able changes are more frequent. . . . Evolution 

 according to the typical Darwinian scheme, 

 through the occurrence of many small variations 

 and their guidance by natural selection, is per- 

 fectly consistent with what experimental and 

 paleontological studies show us; to me it appears 

 more consistent with the data than does any other 

 theory. 



Many believers in mutation have been need- 

 lessly befuddled by the diverse meanings of 

 "variations" as used by Darwin and De 

 Vries. Darwin included in his " individual 

 variations " both the " fluctuating varieties " 

 and the "mutations" of De Vries. Pheno- 

 typically they can not even now be distin- 

 guished. De Vries himself candidly admits 

 that this was Darwin's attitude, thus proving 

 himself more clear-sighted than many of his 

 followers. All that Darwin needed for his 

 purpose was proof of variations that are 

 heritable, and these are found in mutations, 

 be they large or small. 



Just as mendelism has to do with the 

 mechanism and not the fact of heredity, so 

 the mutation theory deals with the nature and 

 not the fact of variations. Neither, in my 

 opinion, has any implication that is antagon- 

 istic to the theory of natural selection. 



The statement has often been made that 

 natural selection " originates nothing " be- 

 cause it does not explain the origin of varia- 

 tions. I must confess to scant patience with 

 this point of view. As well say that the 

 sculptor does not make the statue because he 

 does not manufacture the marble or his 

 chisel ; or that the worker in mosaic originates 

 nothing because he does not make the bits of 

 stone which he assembles in his design! 



The material corresponding to the bits of 

 stone in the mosaic is furnished by heredity 

 and variation, and its quantity by geometrical 

 ratio of increase. Natural selection acts in 

 selecting and putting together this material 

 in the formation of new species. Thus, in a 

 true sense, it seems evident that something 

 new has appeared — something that is but was 

 not. 



Another favorite figure, introduced I be- 



lieve by De Vries, is " Natural selection acts 

 only as a sieve" determining which forms 

 shall be retained and which shall be discarded. 

 This also seems to me to fall short of a com- 

 plete statement of the truth. If the material 

 subjected to the sifting process be regarded 

 as changing with each generation by the addi- 

 tion of variations, or mutations if you prefer, 

 some of which are favorable to a nicer adjust- 

 ment of the species to its environment; the 

 figure would be more nearly correct. To make 

 it complete, however, the mesh of the sieve 

 must change from generation to generation so 

 that a quantitative variation which wouJd be 

 preserved in one generation would be dis- 

 carded in a later one. But in this case nat- 

 ural selection would do more than a sieve 

 could do. It woidd combine a number of 

 favorable variations in the production of 

 something new, a. new species! 



In conclusion it seems to me that we are 

 justified in maintaining that "Mendelism and 

 the mutation theory, while forming the basis 

 of the most brilliant and important advances 

 in biological knowledge of the last half cen- 

 tury, have neither weakened nor supplanted the 

 Darwinian conception of the " Origin of 

 species by means of Natural Selection." 



C. C. Nutting 



SCIENTIFIC EVENTS 



PROFESSOR CALMETTE ON A VACCINE FOR 

 TUBERCULOSIS 



The Paris correspondent of the London 

 Times reports that the Petit Journal publishes 

 an interview with Professor Calmette, sub- 

 director of the Pasteur Institute, which indi- 

 cates that progress has been reached in the 

 long struggle of the medical profession to find 

 a cure for the ravages of tuberculosis. Pro- 

 fessor Calmette was careful to tell his inter- 

 viewer not to proclaim too widely that a cure 

 has been found. " "We are only at the dawn," 

 he said. " The possibilities are immense, I 

 can assure you, but we have still much work 

 before us . . . in following the pathway which 

 now lies oi)en before us and which will lead us 

 perhaps to a splendid realization of our hopes. 

 Hope is now permissible." 



