of Charles Darwin's printed in the Times Week in Review section. (Here's the Darwin Project website.)
Here's Darwin at age 12 complaining about his sister:
Just as I was going, she said she must ask me not a very decent question, that was whether I wash all over every morning — no — then she said it was quite disgustin — then she asked me if I did every other morning, and I said no — then she said how often I did, and I said once a week, then she said of cour you wash your feet every day, and I said no, then she begun saying how very disgusting and went on that way a good while. ...so then I went and told erasmus, and he bust out in laughing and said I had better tell he to come and wash them her self, besides that she said she did not like sitting by me or Erasmus for we smelt of not washing all over, there we sat arguing away for a good while.
And here's a good one for my book, an 1844 letter to a botanist friend:
I have been now ever since my return engaged in a very presumptuous work & which I know no one individual who wd not say a very foolish one.— I was so struck with distribution of Galapagos organisms &c &c & with the character of the American fossil mammifers, &c &c that I determined to collect blindly every sort of fact, which cd bear any way on what are species. — I have read heaps of agricultural & horticultural books, & have never ceased collecting facts — At last gleams of light have come, & I am almost convinced (quite contrary to opinion I started with) that species are not (it is like confessing a murder) immutable. Heaven forfend me from Lamarck nonsense of a “tendency to progression” “adaptations from the slow willing of animals” ... but the conclusions I am led to are not widely different from his — though the means of change are wholly so — I think I have found out (here’s presumption!) the simple way by which species become exquisitely adapted to various ends.