To Leonard Jenyns   14 February [1845]

Dear Jenyns.

I have taken my leisure in thanking you for your last letter, & discussion, to me very interesting, on the increase of species. Since your letter, I have met with a very similar view in Richardson, who states that the young are driven away by the old into unfavourable districts, & then mostly perish.—¹ When one meets with such unexpected statistical returns on the increase & decrease & proportions of deaths & births amongst mankind & in this well-known country of ours, one ought not to be in the least surprised at ones ignorance, when, where & how, the endless increase of our robins & sparrows is checked.—

Thanks for your hints about terms of “mutation” &c; I had had some suspicions, that it was not quite correct, & yet I do not yet see my way to arrive at any better terms: it will be years before I publish, so that I shall have plenty of time to think of better words— Development w^d. perhaps do, only it is applied to the changes of an individual during its growth. I am, however, very glad of your remark, & will ponder over it.

We are all well, wife & children three, & as flourishing as this horrid, house-confining, temper-souring weather permits.—

With thanks, believe me | Your’s very sincerely | C. Darwin