Darwin Correspondence Project

Sept. 30. 1860.

-- I expect that when the nondiversification of rodents, bats, manatees seals &c. on remote Miocene islands is fully worked out, it may merely end in satisfying you & me that the time required for change is longer than was supposed, or without such facts, demonstrable.

It will require renewed enquiry into the antiquity of such islands, also considerations as to the time before first bats & rodents arrived. also the force of preoccupancy—also the arrival of the same species of bats & rodents again & again acting like European colonists into U.S., checking the formation of a new race.

Have you ever speculated in print on turtles changing to land tortoises in remote islands like Galapagos?

From Falunian (Upper Miocene) to Recent is only a part, tho` a large part (23ds) of one geoll. period measured by change of mollusca.

If as a rule a few species even of large genera vary then if bats & rodents migrate into an island the chances may be a thousand to one that these species are among the unpliant, unvarying ones, & if as you say we know nothing of the law which governs the exceptional cases, we cannot conjecture whether insular conditions would favour such divergence if when the thousandth chance did turn up in some island & an insular species was ready to sport & improve & wd. have done so on land far from sea. Perhaps the chief use to make of my difficulty is this, & it accords with my old notion that species as a rule, or the majority of them, are immutable, & have always been so.

Asa Gray is afraid of argument from imperfection of record.

Falconer observes that the Apteryx has strong clavicles & other bird-like characters without wings. I said, the more useless some of these parts not yet suppressed, the more likely to come down from an ancestor who had need & use of them or to be nascent organs advancing towards perfection, for a posterity which wd. enjoy wings. He only laughed as if the whole was a joke, yet I got him to admit that the hypothesis of limited modifiability was quite as arbitrary as yours.

By the way that reminds me that the keel in the middle of the breast-bone is wholly wanting in some (or all?) of the Dinornis family, tho' I think a little remains in the Apteryx & I am almost sure that H. v. Meyer has lately found this keel in the Pterodactyl.

The long duration & numbers of the Ammonities from trias to chalk & then their extinction, tho` high in the scale, is certainly striking. I presume from the myriads of sepia bones which sometimes strew the Jutland coast that naked cuttle-fish now play their part & are higher in the scale, though not higher than belemnites who accompanied ammonites. The vast number & size of Hippurites & their sudden appearance & disappearance, the only extinct order of Mollusca is also very striking. It would not make much impression here as we have few, but in S. of France, Italy, Sicily & all round Mediterranean.

What you say as to my difficulty is I suspect an explanation up to a certain point, but I hope to put the whole more clearly soon. Dogs of multiple origin & leporines would greatly weaken the objection to regarding the negro as of a different species, in the same sense that the Prairie wolf & common wolf may be. I should like a good naturalist to give me a list of reputed species in Mammalia not more remote than negro & white man. Would they not be many?

Instead of Selection I shd have said, Variation & Nat. Selection. My only objection is not to the term, but to your assigning to it more work than it can do & the not carefully guarding against confounding it with the creative power to which ``variation'' & something far higher than mere variation viz. the capacity of ascending in the scale of being, must belong. Most likely you would have chosen some term less worthy of Deification, for 'selection` you had an excellent technical reason.