THE LAMARCKIAN PRINCIPLE 47 



the world. If a bird wins a prize in an important race, its off- 

 spring born before it was highly trained have just as great a 

 market value as those born after. When a race-horse has made 

 a great name, he is often put to the stud and his training is 

 neglected. He is kept in good health, but there is no attempt 

 to further develop his pace. Breeders, then, by their practice, 

 support Weismann. They may hold, it is true, that a particular 

 diet may produce size, and in this view they are undoubtedly 

 correct. But if they assume that the larger build due to such 

 food is inherited, we are at liberty to disagree with them. They 

 not only feed for size, but select for it. The whole result may 

 be due to selection, or, to put it more correctly, those individuals 

 are selected in which the diet in question produces large stature. 

 In the same way, climatic conditions, or the nature of the pas- 

 ture, affect the wool of sheep. A Shropshire sheep, if trans- 

 ferred to the Cotswolds, becomes coarse in the fibre of his coat. 

 The full effect of the new condition is visible in individuals that 

 have been transferred after they have attained maturity?- Further 

 evidence, I think, is wanted before we can agree with Professor 

 Cope that later generations exposed to similar conditions show 

 an accumulated coarseness of wool. 



If we turn to plants, we find the case against Lamarckism still 

 stronger. A gardener is bound to be mainly a Weismannite. 

 He can, it is true, vary the soil, and so, to some extent, the diet 

 of his nurslings, but a plant cannot be trained and exercised as a 

 horse can. The gardener must trust to congenital variations. 

 For these he looks out, and selects the plants that show the 

 qualities that he wants. 



It might be argued that, though other characters are not trans- Disease 

 missible, this can hardly be true of diseases or immunity from 

 them. Yet there is convincing evidence that here too the rule 

 holds good : acquired characteristics are not inherited. 



Civilised man has for many generations been suffering from 

 certain infectious diseases. Among these we may single out 

 measles as a good example for our purpose. Those who have 



1 A noted Shropshire sheep-breeder, whom I have consulted, was most decided on 

 this point. 



