EXPERIENCE NOT HEREDITARY 167 



because, as Professor Meldola has pointed out, 'in 1879 

 the question of the non-transmission of acquired characters 

 had not been brought into prominence. It was tacitly 

 assumed in the theory of Bates that a knowledge of 

 edible and inedible types could be transmitted by heredity. 

 It is remarkable that Miiller, by virtue of his hypothesis, 

 should have unconsciously challenged this tacit assumption 

 by suggesting that young birds had to learn by experience, 

 and did not derive their knowledge of eatable and dis- 

 tasteful forms by heredity. The whole tendency of Pro- 

 fessor Lloyd Morgan's work of late years has been to 

 confirm this suggestion by actual observation and experi- 

 ment ; and Mr. Finn, also, in summing up his results, 

 states that " each bird has to separately acquire its ex- 

 perience, and well remembers what it has learned." Thus 

 the Mullerian theory of 1879 has now been placed on 

 a psychological basis of well-ascertained facts.' 1 



The problem has been attacked from both sides with 

 concordant results. In contemplating the vast scale upon 

 which these aids to memory and education are developed, 

 it is necessary to take into account the pressure of the 

 struggle for existence upon the enemies themselves. 

 ' This pressure is chiefly felt by the young, and it is so 

 excessive that comparatively few individuals in the fresh 

 wave sent forth at each breeding season, survive to 

 become mature and experienced. It follows from this 

 fact that the amount of selective pressure exerted by 

 inexperienced enemies of insects is many times as great 

 as that which is due to the educational period of the 

 mature enemies existing at any moment.' 2 We also realize 



1 Nature, vol. lx, 1899, p. 57. 



2 Proc. Enl. Soc, Lond., 1503, p. Ixv. The form of the passage has 

 been slightly modified. 



My kind friend Dr. A. R. Wallace, D.C.L., F.R.S., wrote (April 3, 

 1905) concerning these quoted sentences — 'There is one short passage 

 . . . which I had to read two or three times to see the point, which is 

 quite sound but too condensed. ... It wants much amplifying to make it 

 clear. . . .' 



The argument may be stated in another and I hope clearer form, as 

 follows : — 



The numbers of the species keeping approximately constant over 

 a long period of time, we are compelled to suppose that each pair of 



