SOME IMPLICATIONS OF THE 

 CHROMOSOME THEORY OF HEREDITY 



By JULIAN S. HUXLEY, M.A. 

 New College, Oxford 



The history of science shows us that new ideas generally gain 

 acceptance not so much by defeating the old in controversy, 

 but by supplanting them — by competition, not by battle. 



The divergences of opinion between Professor MacBride 

 and myself, as expressed in the correspondence section of 

 the last issue of Science Progress, have reimpressed this truth 

 upon me. Controversy is really of little use in settling such 

 disputes. Far better for each party to put forward their own 

 positive construction, and let the world decide between the two 

 presentations. 



Professor MacBride has already set forth his views on 

 the subject (Science Progress, Jan. 192 1) ; I would crave 

 indulgence to bring forward some of the general implications 

 of that alternative theory which advances furthest in the 

 opposite direction — the chromosome theory of Morgan and his 

 school, which, combining the Mendelian theory of segregation 

 with the mutation hypothesis, grafts both on to a cytological 

 basis. 



I shall endeavour to summarise very briefly the chief lines 

 of evidence upon which the hypothesis is based, and then to 

 point out some of the implications of the theory which are 

 usually not dealt with in the textbooks on the subject : 

 Throughout, I shall have to assume acquaintance with the 

 ordinary facts of genetics and cytology as they may be found 

 set forth in standard works such as Punnett's Mendelism, Baur's 

 Einfuhrung in die experimentellen Vererbungswissenshaft, Don- 

 caster's Cytology, etc. 



In the first place, then, we have the well-known facts 

 of Mendelian inheritance. Most of these can be explained on 

 the hypothesis introduced by Mendel himself, that visible 

 characters of the adult organism were in some way represented 

 in the germ from which it arises by discrete units, each one 

 independent of the others. These units, usually styled unit- 

 factors, or more briefly genes, are normally present in pairs ; 

 but the members of a pair separate from each other at some 



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