Apparently, Charles Darwin said that when he heard something that did not fit his theory, he wrote it down, otherwise he tended to forget it.

Can anyone give me a reference for this?

Thanks!

UPDATE: Thanks to David Schweiger (via Steven Hamblin’s blog), we have the answer. It’s from Darwin’s Autobiography (p. 123):

I had also, during many years, followed a golden rule, namely, that whenever a published fact, a new observation or thought came across me, which was opposed to my general results, to make a memorandum of it without fail and at once; for I had found by experience that such facts and thoughts were far more apt to escape from the memory than favourable ones. Owing to this habit, very few objections were raised against my views which I had not at least noticed and attempted to answer.