NATURE 



i8] 



THURSDAY, MAY 3, 1917. 



THE PROBLEM OF HEREDITY. 



A Critique of the Theory of Evolution. By Prof. 

 T. H. Morgan. Pp. x + 197. (Princeton: 

 University Press; London: Oxford University 

 Press, igi6.) Price 65. net. 



THE title of this little volume of four lectures 

 delivered at Princeton University is likely to 

 cause some disappointment. The book is almost 

 entirely an exposition of certain facts as to in- 

 heritance ascertained by experiments with the 

 fruit-fly, Drosophila ampelophila, and "a review 

 of a long- series of researches as to the nature of 

 the hereditary material." The author claims that 

 " the mechanism of heredity has been discovered " 

 and that "the problem of heredity has been 

 solved." He holds that "the mechanism of the 

 chromosomes offers a satisfactory solution of the 

 traditional problem of heredity." 



Whilst all credit is due to Prof. Morgan for his 

 long and careful investigations — which have been 

 published elsewhere and are here summarised with 

 excellent diagrams — it cannot be admitted that 

 the demonstration of the numerical relations of 

 the chromosomes distributing to the germ-cells 

 the hereditary factors carried by the parents is 

 of the importance which he supposes. The 

 " traditional problem of heredity " cannot be cor- 

 rectly described as limited to the inquiry as to 

 what are the carriers of the factors of heredity and 

 their relations to one another as carriers. The 

 questions as to how the factors arise and how 

 they influence the development of the embryo 

 cannot, as Prof. Morgan somewhat arbitrarily 

 states (in so many words), be excluded from a 

 solution of the real, traditional, and actual pro- 

 blem of heredity. The fact seems to be that the 

 knowledge of what is called "Mendelian inherit- 

 ance " and the relation to it of the chromosome 

 mechanism does not take us much further into 

 the " problem of heredity " than we had already 

 got when, after Darwin had stated the facts 

 known to him and the views they suggested In his 

 "Animals and Plants under Domestication," 

 Edouard Van Beneden and other histologlsts 

 first unravelled the chromosomes and gave us the 

 classical records of their visible activity in fer- 

 tlllsatlorr. 



We have not got much further since those 

 days, but there Is no doubt that some facts of 

 Interest have been added to the stock of know- 

 ledge by those who have confirmed MendeJ's ex- 

 periments. When we look to the present sum- 

 mary for some statement of what important 

 progress In our conception and understanding of 

 inheritance Is to be reported, we are reluctantly 

 driven to the conclusion that what Prof. Morgan 

 calls "a satisfactorv solution of the traditional 

 problem of heredity " Is only a restatement of the 

 problem In terms of Invisible " factors " asso- 

 ciated with the chromosomes. The existence of 

 such " factors " Is not a new Inference, but has 

 been a feature of theories of inheritance both 



NO. 2479, VOL. 99] 



before and since Darwin's treatment of the subject- 

 Mendel contributed to knowledge the solid fact 

 that in certain easily observed cases (if not 

 universally) a pair of opposed or contrasted fac- 

 tors — present one in one parent and one in the 

 other — do not really "blend" in cross-breeding, 

 but in successive in-bred generations of the 

 hybrid off^spring (of intermediate or mixed 

 character) become separated out in two pure races, 

 each identical, 'SO far as the factor selected, for 

 study is concerned, with one of the original cross- 

 bred parents. That observation and its extensive 

 confirmation are important steps in the study of 

 the nature, origin, and possibilities of the "fac- 

 tors." So also is the demonstration of their close 

 association with the chromosomes, which was 

 suggested as soon as the activity of those struc- 

 tures in the process of fertilisation was first 

 observed. 



This is, however, only a beginning : it 

 remains to be seen how far the application oF 

 these results to the actual facts of inheritance as 

 stated by Darwin In the successive chapters of 

 his " Variation of Animals and Plants under 

 Domestication " helps us to explain or understand 

 those facts. So far the application has not been 

 made — so as to obtain any result beyond a re- 

 statement of the facts . in other terms and 

 language — nor does there appear to be. any 

 immediate prospect of progress in that direction. 



An important suggestion is made by Prof. 

 Morgan, namely, that the "factors" themselves 

 may vary or fluctuate.. H.e says : " I do not know 

 of any a priori reason why a factor may not 

 fluctuate, unless it is, as I like to think, a chemical 

 molecule." He, however, proceeds to give 

 evidence opposed to such fluctuation. 



It seems that the line of investigation pursued 

 by Prof. Morgan and other recent experimenters 

 who have developed Mendel's original observa- 

 tions into an Imposing volume of detail 

 has disappointed expectation. It will, we 

 believe, be of service, but it has, to the 

 regret of all, not led into the fruitful 

 region anticipated by those who entered upon it 

 with so much enthusiasm and energy. In order 

 to gain a deeper understanding of the many 

 remarkable facts of organic heredity a new 

 departure Is necessary, pew inductions suggesting 

 new and untried lines of observation and experi- 

 ment. 



So far as the title of these lectures, "\ 

 Critique of the Theory of Evolution," is concerned, 

 there is very little said in them which justifies It. 

 Prof. Morgan objects to the use of the word 

 "evolution" as employed by Herbert Spencer, 

 en the ground that it Is " rather an empty 

 generalisation to say that any kind of change is 

 a process of evolution. . . . What has," he asks, 

 " the evolution of the stars, of the horse, and of 

 human inventions In common?" This seems to be 

 somewhat unnecessary, since no one has said that 

 "any and every kind of change is a process of 

 evolution," and the instances of evolution which 

 he cites have, as such, well- recognised features 

 in common. Attempts to correct flagrant misuse 



