East: As Genetics Comes of Age 



211 



transmit different characters, would be 

 less likely to appear so puzzling if 

 this were clearly recognized. And even 

 if we admit our inability at present to 

 contribute much toward the solution 

 of the question, so well delimited by 

 Weismann, of somatic specialization 

 during the development of the individ- 

 ual, one cannot but feel that further 

 progress in dealing with problems of 

 straight heredity- will ultimately be 

 helpful. 



As to the grand problem of evolu- 

 tion, I believe there has been a con- 

 crete offering. True, the question 

 of "how" is still in statu quo: but one 

 must be rather a pessimist if he does 

 not consider that the current concep- 

 tion of the gene presents something 

 tangible on the subject. It certainly 

 allows a definite distinction between 

 variations due to environmental fluc- 

 tuations, variations due to rearrange- 

 ments and combinations of genes, 

 and variations due to change in the 

 constitution of the unit of heredity 

 itself. Furthermore the data now 

 being gathered on the type of gene 

 changes occurring, and on the fre- 

 quency with which they take place, 

 are not to be cast aside as of no value 

 to the evolutionist. A statement as 

 to just what they mean would be a 

 daring assertion, but that they mean 

 something now and will mean more 

 later cannot be doubted. 



Let us take, for example, the fol- 

 lowing illustrations, which, I think, 

 are fair. 



1. Mutations (Gene variations) are 

 now occurring in all species that have 

 been investigated intensively. 



2. There is a wide range to mutation 

 frequency in different species. 



3. The number of useless or of harm- 

 ful mutations is many times the number 

 of useful or of heneficient mutations. 



4. The number of mutations affect- 

 ing chiefly certain organs or particular 

 tissues greatly exceeds those affecting 

 other parts of the individual. 



5. The "conservative" parts as meas- 

 ured by mutation frequency, appear 

 to have slight relation to the "conserva- 

 tive" parts as determined by the 



circumstantial evidence of the phylo- 

 genist. For example, loss of the ligule, 

 a characteristic of the grass family, 

 has been found in a goodly number of 

 the cultivated grasses, — these being 

 the only ones that have been studied 

 very carefully. 



6. Mutations are often reversible. 

 Re\^ersibility may not be universal, 

 though the mere fact that it has not 

 been observed in every case proves 

 only that the reaction does not take 

 place in both directions with the same 

 ease. 



7. Mutations which from their 

 major effects can be arranged in a 

 graded series, — for example, eye color 

 of Drosophila melanogaster, — are found 

 not to have originated in that order. 

 That is to say, such orthogenetic 

 phenomena as have been observed are 

 better interpreted as analogous to 

 chemical phenomena, where tendency 

 to certain reactions is greater than to 

 others, than as "vital force" phenom- 

 ena. 



No one can maintain that these 

 genetic findings compare with the 

 fundamental laws of thermodynamics 

 in elegance and simplicity. No one 

 can say how general they are. But 

 fruit flies and maize, rodents and peas, 

 upon which the observations were 

 largely made, are pretty far apart in 

 the general scheme of things; therefore 

 it would be very odd indeed if they 

 should turn out to be special cases. 

 And to me they are very helpful to a 

 clearer general conception of evolution. 



THE MECHANISM OF HEREDITY 



Turning now to the mechanism of 

 heredity, let us see what can be said. 

 The main generalization is that there 

 are units of inheritance, the genes, 

 which are constant in the sense that 

 stable chemical compounds are con- 

 stant; and whose distribution follows 

 the distribution of the chromosomes. 

 In other words, the discoveries of 

 experimental genetics have made it 

 possible to endow the conceptual units 

 of earlier days with particular qualities, 

 just as discoveries in the physical 

 sciences have made it possible to 



