CORRESPONDENCE 45 1 



chromosome maps, whilst we admire the boldness and ingenuity of the 

 hypothesis, we are assailed by serious doubts. 



Great is the suggestive power of confident assertion, and we have con- 

 stantly to remind ourselves that when Prof. Morgan and Mr. Huxley tell us 

 that the " gene " or factor which controls eye-colour in the fly Drosophila is 

 " located " at a particular spot in a certain chromosome, they have only 

 the evidence that white eye-colour for example is " linked " with certain 

 other characters. Now, Mr. Huxley tells us that eye-colour is controlled, 

 not only by a gene in one chromosome, but by several other genes situ- 

 ated in different chromosomes as well ; this means, in fact, that the original 

 hypothesis on which the whole location of the gene was founded has turned 

 out to be illusory, and that eye-colour may be linked with quite different 

 characters from those with which it was first found associated ; but this 

 distressing discovery is carefully masked by the imaginary construction of 

 two totally distinct genes producing the same result. 



But whether this assumption of the specific character of chromosome 

 regions is ultimately justified in whole or in part, or not, is totally irrelevant 

 to the points at issue between Mr. Huxley and myself, and it is only in respect 

 to these points that his theory becomes in any sense alternative to mine. 



These points are two in number, viz. : (i) Mr. Huxley regards the abnormal 

 specimens which turned up in Morgan's cultures of the fly Drosophila as fair 

 samples of the kind of variation with which natural selection has worked in 

 bringing about the evolution of existing plants and animals, whereas I 

 insist that these " mutants" are degenerative teratological specimens, whose 

 divergence from the type resemble in no way the changes which have taken 

 place during the course of evolution, and (2) Mr. Huxley maintains that 

 there is no evidence for the inheritance of acquired characters. I believe, 

 on the contrary, that there is strong evidence that acquired characters are 

 inherited, and that this kind of inheritance gives us the key to the under- 

 standing of the evolutionary process. 



To take the first point first. The greatest advance in Mendelian theory, 

 since the days of Mendel, was that made by Bateson and Punnet, when they 

 showed that the difference between dominant and recessive allelomorphs 

 consisted in the absence in the recessive of a factor which was present in the 

 dominant. One is staggered by the calm assurance with which Mr. Huxley 

 informs us that this theory is being " gradually given up." By whom is 

 the theory being given up, we should ask, and why ? It is true that Morgan 

 does not like it, and seeks to evade it, because he sees clearly what it implies, 

 but in this he is not followed by English Mendelians, and with justice, for the 

 facts are loud-voiced in its favour — a single instance will make this clear. 

 The albino fly, and, for that matter, the albino mouse, is recessive, when crossed 

 with this type. In the case of the mouse, Cuenot proved that albinism is 

 due to the absence of a substance which he called chromogen, whose action 

 was necessary in order that the colour-producing elements should make 

 themselves effective. That something is defective in the albino is also 

 clearly shown by its general weakness of constitution as compared with the 

 type. Now, if the material basis of inheritance lies in the chromosomes it is 

 an irresistible inference that, when a weak and defective individual is pro- 

 duced, the chromatin from which it took its origin must have suffered damage. 

 We know that if the spermatozoa of the frog be exposed to the harmful 

 influence of radiations from radium, and then used to fertilise normal ova, 

 monstrous tadpoles will be produced. In the case of the albino fly complete 

 loss of pigment is confined to the eye ; but the accompanying weakness of 

 constitution is no less marked. But it may be replied there are other colours, 

 besides pure white, which are recessive to the type colour. These other 

 colours — eosin and cherry-red, for instance — show the same linkage as 

 albinism, and are supposed to be due to genes which have their location in 



