CORRESPONDENCE 643 



sufficient number of hypothetical factors, and explain every failure to 

 segregate as due to the interference of factors. 



Thus extended, the Mendelian hypothesis becomes totally indifferent to 

 the facts ; whichever way these turn out, it may be made to fit by making 

 some additional assumptions, and it is impossible to devise a crucial experi- 

 ment. This is the pass to which some of the factor-mad pupils of Prof. 

 Morgan have reduced the theory, and at this point it ceases to interest the 

 serious biologist, whether he label himself geneticist or not. 



Again, although I do not beUeve that the mutations experimented with 

 by Mendelians have played any part in evolution, I should be the last to 

 "belittle" the importance of their discoveries. They are, I think, of prime 

 importance for the human race where our outlook is limited to two or three 

 generations, and where the efforts of our sickly sentimentalists to keep all 

 our MendeUan defectives alive, and encourage them to breed, are threatening 

 the future of our race. 



Turning now to the second point, viz. Dr. Huxley's criticisms of the 

 evidence which I brought forward in favour of Lamarckism, the impression 

 made on my mind is that he must be in a state of profound ignorance of 

 the whole subject. Thus, he states that my argument about lens determiners 

 recalls the " delicious blends of thirty years ago — when Weismann was to 

 the fore." But this case was raised by me to show the untenability of the 

 Weismannian theory, which is at bottom identical with the Mendelian 

 theory. If I turn to Goddard, Feeble-mindedness, its Causes and Consequences, 

 a book which contains the Mendelian discovery of most practical importance 

 yet reached, we find that he speaks of " determiners," and of the large 

 number of these " determiners " which must be present in the spermatozoon. 

 Yet Dr. Huxley states that Mendelians prefer to talk in terms of " organic 

 equilibrium " ! He further states that the abnormal formation of the lens 

 " is infinitely harder to explain on Lamarckian principles." 



Now, " organic equilibrium " is a physiological conception, and, may I 

 add, a Lamarckian one, and the aberrant formation of the lens is just what 

 we should expect if Lamarckism were true. For, according to Lamarckian 

 theory, organs arise as a response by the organism to the demands of the 

 environment. But the environment is internal as well as external, and one 

 organ within the body is, so to speak, an environment for another, and 

 should exercise a modifying influence on it. Then he says that my statement 

 that "it is by no means easy to find on it an animal which will respond to 

 a change of the environment by a change of structure " detracts from the 

 importance of Lamarckism as an evolutionary factor. Now, Lamarck ex- 

 pressly states that the changes which he postulates will only become apparent 

 after a long time, i.e. after many generations. It is a matter of great luck 

 that in Amphibians we seem to have a stock sufficiently plastic to show an 

 observable difference in two or three generations. 



All our available evidence goes to prove that the evolutionary process 

 was extraordinarily slow. My colleague. Lord Rayleigh, tells me that he 

 has determined the minimum age of some Oligocene beds from their heUum 

 contents, and it turns out to be 30,000,000 years ! and yet all this time 

 was required to convert the three-toed Mesohippus into the one-toed horse. 



Lastly, Dr. Huxley attacks the relevance of the experiments recorded in 

 Guyer's work to the point at issue. Their relevance is strongly asserted 

 by Guyer himself, who points out that they afford an explanation of the 

 diminution of the eyes of cave-animals. The fact that the original vestigial 

 lens was produced by a lens-destroying serum, and that such an occurrence 

 is not met with in Nature is totally irrelevant. The important point is 

 that, once the defective lens was produced, it was propagated through several 

 generations — without any further use of serum. The influence of the soma 

 on the germ, which Dr. Huxley states that no " learned biologist " would 



