CHAPTER XXXV 



THE ORIGIN OF NEW HEREDITARY CHARACTERS 



While it may be said that the problems of the modes and mecha- 

 nisms of heredity have absorbed the chief attention of geneticists during 

 the last quarter of a century, interest seems to be now more and more 

 strongly directed to problems of variation. During the previous vogue 

 of variation studies the method of attack was entirely statistical and 

 the results were, on the whole, rather unfruitful and disappointing. 

 The present return to a study of variation is to be explained by the 

 facts, first, that the problem of heredity seems to be well-nigh solved 

 in its broader aspects; second, that studies of heredity have of ne- 

 cessity concerned themselves with variations (mutations) as they have 

 arisen in pedigreed stocks; and third, that considerable light as to 

 the nature and causes of mutations has been gained through the modes 

 of analysis used in careful Mendelian experiments, it now appears 

 that the most pressing problem before geneticists today is that of the 

 causes of mutations, and a massed attack upon this problem is getting 

 well under way. 



Two lines of investigation are being pursued, one of which in- 

 volves the working hypothesis that variations take place originally in 

 somatic tissues as the result of use or disuse and changed environment 

 (the inheritance of acquired characters) ; while the other assumes that 

 the germ cells are the original seat of all hereditary changes, whether 

 they arise spontaneously through interactions within the germinal 

 substance itself or are induced by changes in the environment (the 

 mutation theory). There are today two rival schools of geneticists; 

 (a) the minority school of neo-Lamarckians, backed by many physi- 

 ologists, sociologists, educators, and some animal-breeders; and (6) 

 the majority school of the neo-Mendelians, mutationists, and a repre- 

 sentative body of professional biologists. 



The orthodox geneticist declares that there is not a smgle bit of 

 holeproof evidence that somatic modifications are inherited, and 

 abundant evidence, both logical and experimental, that they cannot be 

 inherited and, in fact, never are inherited. The advocates of the 



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