DARWIN 21 



of Abyssinia. I look at it as certain that these plants crossed 

 the whole of Africa, from east to west, during the same period. 

 I wish I had published a long chapter, written in full, and 

 almost ready for the press, on this subject which I wrote ten 

 years ago. It was impossible in the ' Origin ' to give a fair 

 abstract " (" More Letters," vol. i., p. 476). Having thus held 

 his views for twenty-five years, they had become so firmly 

 impressed upon his mind that he was unable at once to give 

 them up, however strong might be the arguments against 

 them. This particular difference, however, is not one which 

 in any way affects the theory of natural selection. 



4. Pangenesis, and the Heredity of Acquired Characters. — 

 Darwin always believed in the inheritance of acquired charac- 

 ters, such as the effects of use and disuse of organs and of 

 climate, food, etc., on the individual, as did almost every 

 naturalist, and his theory of pangenesis was invented to explain 

 this among other effects of heredity. I therefore accepted 

 pangenesis at first, because I have always felt it a relief (as 

 did Darwin) to have some hypothesis, however provisional 

 and improbable, that would serve to explain the facts; and I 

 told him that " I shall never be able to give it up till a better 

 one supplies its place." I never imagined that it could be 

 directly disproved, but Mr. F. Galton's experiments of trans- 

 fusing a large quantity of the blood of rabbits into other 

 individuals of quite different breeds, and afterwards finding 

 that the progeny was not in the slightest degree altered, did 

 seem to me to be very nearly a disproof, although Darwin did 

 not accept it as such. But when, at a much later period, Dr. 

 Weismann showed that there is actually no valid evidence 

 for the transmission of such characters, and when he further 

 set forth a mass of evidence in support of his theory of the 

 continuity of the germ-plasm, the " better theory " was found, 

 and I finally gave up pangenesis as untenable. But this new 

 theory really simplifies and strengthens the fundamental doc- 

 trine of natural selection. 



It will thus appear that none of my differences of opinion 

 from Darwin imply any real divergence as to the overwhelm- 



