The Modern Idea of Evolution 



15 



ing evolution with the material on 

 which natural selection works. If we 

 accept for the moment this statement 

 as the cardinal doctrine of natural 

 selection it appears that evolution is 

 due (1) not to an orderly response of 

 the organism to its environment, (2) 

 not in the main to the activities of the 

 animal through the use or disuse of its 

 parts, (3) not to any innate principle of 

 living material itself and (4) above all 

 not to purpose either from within 

 or without . Darwin assumed that small 

 variations are constantly appearing in 

 a species, and that individuals with 

 favorable variations survive and trans- 

 mit them to their descendants, those 

 with unfavorable variations perish. 



Darwin's original contribution was not 

 to demonstrate that evolution existed. 

 That fact had long been recognized in 

 speculation and later received over- 

 whelming proof from comparative anat- 

 omy, embryology, paleontology and 

 breeding. All of this evidence showed 

 that living species were related to each 

 other, that they had so much in common 

 as to force the assumption that they 

 came from common ancestors ; and pale- 

 ontology was even able to bring for- 

 ward some of these common ancestors. 



The question was not to show that 

 divergent forms had a common origin, 

 but to explain how they had come to 

 diverge, and Darwin's explanation of 

 the action of natural selection on in- 

 heritable variations was generally ac- 

 cepted as accurate. But his attempts 

 to explain (1) the origin of these varia- 

 tions and (2) the manner in which they 

 were inherited met with little success, 

 and as long as these two problems were 

 unsolved, the evolutionist was on uncer- 

 tain ground. 



RECENT PROGRESS GREAT 



Biologists, therefore, made a wide- 

 spread attack on these two problems, 

 and it is the belief of many that within 



the last decade (2) has been explained 

 and (1) has been considerably elucidated,, 

 although not yet solved. 



This is the viewpoint taken by Prof. 

 Thomas Hunt Morgan, of Coliimbia 

 Univeristy, who has brought together 

 in book form^ four lectures in which 

 he critically examines the theory of 

 evolution. In addition to its intrinsic 

 merits, the book has added interest 

 because, in the first place. Dr. Morgan 

 was one of the first zoologists success- 

 fully to challenge the adequacy of Dar- 

 win's explanations, and still more, in 

 the second place, because his own work 

 has been very largely responsible for 

 clearing up problem (2) above-men- 

 tioned, the problem of how variations 

 are inherited. The book is simply 

 written, and furnishes the first authori- 

 tative account of Morgan's work which 

 is available to anyone but the specialist, 

 Morgan's previous works having been 

 too technical for comprehension by the 

 reader who had no previous knowledge 

 of genetics. 



The preceding paragraphs have 

 summed up Morgan's statement of the 

 case. We have evolution as a theory, 

 many attempts to demonstrate it, and 

 finally general agreement that Dar- 

 win had demonstrated it successfiilly. 

 Then we see certain fundamental parts 

 of Darwin's proof challenged and, by 

 many critics, thrown out of court. 

 The questions of (l)how variations origi- 

 nated and (2) how they were inherited had 

 to be attacked again, and they were fun- 

 damental to the problem. Dr. Mor- 

 gan's book is mainly devoted to an ex- 

 planation of his views on these two- 

 points. 



We can dispose of the first of these- 

 points quickly, for the problem it pre- 

 sents has not yet been solved. Darwin: 

 borrowed Lamarck's view, that varia- 

 tions originated through the activities, 

 of the animal, and whatever could not 

 be explained by this he admitted to be 



1 A Critique of the Theory of Evolution, by Thomas Hunt Morgan, professor of experimental 

 zoology in Columbia University. Lectiires delivered at Princeton University in February and 

 March, 1916. Pp. 197, price $1.50. Princeton University Press. The book is lavishly illus- 

 trated with 95 figures, but many of them are hackneyed or inartistic. Someone could perform a 

 great service to evolutionists by getting together a new set of illustrations to take the place of those 

 that have been doing duty so long. 



