18 PHYSICAL BASIS OF HEREDITY 



the soma. Until physiological chemists are in position 

 to furnish more complete information concerning the com- 

 position of the chromosomes, or more illuminating criti- 

 cism of the situation as it exists, we need not, I think, 

 be over-much troubled by such views so long as we handle 

 our own data in a manner consonant w^ith the recognized 

 methods of scientific procedure. 



Other critics object for one reason or another to all 

 attempts to treat the problem of heredity from the stand- 

 point of the factorial hypothesis. It has been said, for 

 instance, that since the postulated genetic factors are 

 not known chemical substances the assumption that they 

 are such bodies is presumptuous, and gives a false analogy 

 with chemical processes. Such critics claim that the pro- 

 cedure is at best only a kind of symbolism. Again, it has 

 been said, that the factorial hypothesis is not a real 

 scientific hypothesis, for it merely restates its facts in 

 terms of factors, and then by juggling with numbers pre- 

 tends that something is being explained. It has been 

 argued that Mendelian phenomena relate to unnatural 

 conditions and that they have nothing to do with the 

 normal process of heredity in evolution that takes place 

 in ^'nature." It has been objected that such a hypoth- 

 esis assumes that genetic factors are fixed and stable in 

 the same sense that molecules are stable, and that no such 

 hard lines are to be found in the organic world. And 

 finally it has been urged that the hypothesis rests on dis- 

 continuous variation which, it is said, does not exist. 



If the implications in any or in all of these objections 

 were true, the attempt to explain the traditional prob- 

 lem of heredity by the factorial hypothesis would 

 appear fantastic in the extreme. An attempt will be 

 made in the follomng chapters to present the evidence 

 on which our present views concerning heredity rest, in 

 the hope that an understanding of this evidence will go 

 far towards removing these a priori objections, and will 

 show that they have no real foundation in fact. 



