And if this be so, why may I not invent the hypothesis of Natural Selection (which from the analogy of domestic productions, and from what we know of the struggle for existence and of the variability of organic beings, is, in some very slight degree, in itself probable) and try whether this hypothesis of Natural Selection does not explain (as I think it does) a large number of facts in geographical distribution--geological succession, classification, morphology, embryology, etc.

I should really much like to know why such an hypothesis as the undulation of the ether may be invented, and why I may not invent (not that I did invent it, for I was led to it by studying domestic varieties) any hypothesis, such as Natural Selection.
Pray forgive me and my pen for running away with me, and scribbling on at such length.
I can perfectly understand Sedgwick (100/5.

See "Life and Letters," II., page 247; the letter is there dated December 24th, but must, we think, have been written in November at latest.) or any one saying that Natural Selection does not explain large classes of facts; but that is very different from saying that I depart from right principles of scientific investigation.
LETTER 101.

TO J.S.HENSLOW.

Down, May 14th [1860].
I have been greatly interested by your letter to Hooker, and I must thank you from my heart for so generously defending me, as far as you could, against my powerful attackers.