122 Life and Letters of Francis Galton 



Galton, as I have often informed the reader, was ever young, ever believed 

 that his fellow mortals had the same enthusiasm for the acquisition of 

 knowledge that he himself had, and was always trustful that they would act 

 as dispassionately in assessing their fellow mortals as he himself acted. Thus 

 he launched his schedules and seemed never discouraged even when they 

 brought little or no harvest ! 



In the January number of the Monthly Review for 1903 Sir Edward Fry 

 published a paper entitled: "The Age of the Inhabited World." In this 

 paper he endeavoured to show that Natural Selection is incapable of doing 

 much that has been accredited to its agency, especially citing the case of 

 mimetic insects. He wrote : 



" ...useful deception will not take place until the protected form is nearly approached. Thus 

 during the whole interval occupied in passing from the normal form of group A to near the 

 normal form of group B, natural selection will have been entirely inoperative.... Either birds 

 are deceived by a small amount of imitation or they are not. If they are, natural selection can- 

 not have produced perfect imitation; if they are not so deceived, then group A has passed over 

 from its original form to something close upon the form B without any guidance from this 

 principle." 



Galton criticised this statement in Nature, February 12, 1903 (Vol. lxvii, 

 p. 343) in a letter entitled: "Sir Edward Fry and Natural Selection." He 

 writes : 



"I deny this sharp dilemma and assert the existence of many intermediate stages. Two 

 objects that are somewhat alike will be occasionally mistaken for one another when the condi- 

 tions under which they are viewed are unfavourable to distinction. The light may be faint, 

 only a glimpse of them may have been obtained, the surroundings may confuse their outlines*. 

 While these conditions remain unchanged, the frequency of mistake serves as a delicate 

 measure of even the faintest similarity. .., If one edible group A has individual peculiarities 

 within the limits of variation, that give it a resemblance, however slight, to one of the noxious 

 group B, it will occasionally be mistaken by a bird for a B and allowed to live unharmed. The 

 similarity may be due to a characteristic attitude, to a blotch of colour, to a preference for 

 resting on a part of the foliage to which its own form bears some likeness, or to other causes. 

 In any case, it may well prove to be the salvation of 1, 2 or more per cent, of those who would 

 otherwise have been seen and eaten. If so the thin edge of natural selection will have found an 

 entrance, and its well-known effects must follow." 



It will be noted that Galton says "within the limits of variation." That 

 point is so often overlooked that I must again emphasise it. Few biologists 

 have ever measured the blotch or spot on a butterfly's wing in the case of 

 400 or 500 members of the same species. They think in terms of a type 

 specimen and suppose the type of one species has to be gradually shifted 

 by small stages to the type of another. But the absolute range of variation 

 may possibly be 25 °/ e °f the type value f. Stringent selection for one or two 

 generations may easily raise the type 10 °/ o or 15 °/ o . Such selection is not 

 the same thing as proceeding by minute stages. 



* I think Galton is here thinking of his own experimental work on degrees of resemblance 

 and the use of blurrers: see our Vol. n, pp. 329-333. 



t The mean length of thigh bone in the type Englishman is say 447 mm., but the range of 

 English thigh bones runs from 381 to 513, a range practically covering the type of all existing 

 races. If existence for man depended on the length of his thigh bone there is nothing to prevent 

 severe selection — say the destruction of all individuals with thigh bones over 400 mm. — lowering 

 the English thigh bone to the value, 411 mm., of the Fuegian even in a couple of generations. 



