To Leonard Jenyns [28 April 1858]1
Moor Park, Farnham | Surrey
My dear Jenyns.
I return by this days post your M.S. & extremely much obliged I am for the loan.2 Several of the facts were new to me & I was especially interested by discussion on the Wagtails.3 The notes you kindly said I might retain.4 The selection of facts & not giving too many is one of my chief difficulties— I wish I could swallow Prevost’s statement about the Sparrows, which was one of the cases, which I thought of giving.—5 I have given a short discussion, leading to the conclusion that “secondary sexual characters” were the most variable of all (under domestication & in nature) & several of your facts seem to bear this out.—6
Gould repudiates the statement about the Swallows at Malta & says it was a blunder of Wollaston.7
The pied Raven of Faroe is a good case of an incipient local race, yet sometimes crossing with common form.
I can afford only one long chapter to actual cases of variation in nature; for the mere accumulation of facts becomes, I think, intolerably dull.
It seems to me more important to try & make out a little, (& but a very little) about laws of variation in domestic animals & plants, & secondly to see how far general facts in Nat History & Geology seem best explained by each species having been separately created or having descended, like varieties, from other species. At least this is the way I mean to treat my work.—
Can you give me any facts on variations of Birds nests? more especially of same species in different countries.— I have treated this subject at some little length, as being the best case for showing variation of Instincts.8
With very many thanks | Yours most truly | C. Darwin
One chief reason why I have not accumulated more facts of variation in state of nature is, that naturalists so invariably turn round & say oh they are not varieties, but species.—
Returns MS [of "Variation of species"]; several facts were new to him, especially interested in wagtails.
Wishes he could swallow Florent Prévost on sparrows ["Du régime alimentaire des oiseaux", C. R. Hebd. Acad. Sci. 46 (1858): 136–8].
LJ’s facts seem to bear out CD’s conclusion that secondary sexual characters were most variable of all.
Explains how he intends to deal with variation, and general facts in natural history in the light of species theory. Can only afford one chapter on variation in nature. It seems more important to make out variation in domestic animals.
Asks for facts on birds’ nests for his chapter on instincts.