My dear Lyell

I have been much interested by your letter of 28^th, received this morning. It has delighted me, because it demonstrates that you have thought a good deal lately on Nat. selection. Few things have surprised me more than the entire paucity of objections & difficulties new to me in the published reviews. Your remarks are of a different stamp & new to me. I will run through them & make a few pleadings such as occur to me.

I put in the possibility of Galapagos having been continuously joined to America out of mere subservience to the many who believe in Forbes’ doctrine,¹ & did not see the danger of admission; about small mammals surviving there in such case. The case of Galapagos, from certain facts on littoral sea-shells, (viz Pacific ocean & S. American littoral species) in fact convinced me more than in other case of other islands that Galapagos had never been continuously united with the mainland: it was mere base subservience & terror of Hooker & Co.—²

With respect to atolls I do not think mammals w^d. hardly survive very long even if main islands (for as I have said in Coral-Book outline of groups of atolls do not look like a former continent)³ had been tenanted by mammals, from the extremely small area, the very peculiar conditions, & the probability that during subsidence all or nearly all atolls have been breached & flooded by sea many times during their existence as atolls.—

I cannot conceive any existing reptile being converted into a Mammal. From homologies I sh^d. look at it as certain that all Mammals have descended from some single progenitor. What its nature was, it is impossible to speculate. More like, probably, the Ornithorhynchus or Echidna than any known form as these animals combine Reptilian characters (& in lesser degree Bird character) with Mammalian. We must imagine some form as intermediate as is Lepidosiren now in between Reptiles & Fish, between Mammals & Birds on the one hand (for they retain longer the same embryological character) & Reptiles on the other hand. With respect to a mammal not being developed on any island, besides want of time for so prodigious a development, there must have arrived on the island, the necessary & peculiar progenitor having characters like the embryo of a mammal, & not an already developed reptile, Bird or Fish.— We might give to a Bird the habits of a mammal, but inheritance would retain almost for eternity some of the bird-like structure, & prevent our new creation ranking as a true mammal.—

I have often speculated on antiquity of islands, but not with your precision or at all under the point of view of Natural selection not having done, what might have been anticipated. The argument of littoral miocene shells at Canary Is^d is new to me.— I was deeply impressed from amount of denudation of antiquity of St. Helena, & its age agrees with peculiarity of Flora.—

With respect to Bats at N. Zealand (N.B there are 2 or 3 Europeans Bats in Madeira & I think in Canary Islands) not having given rise to group of non-volant &c Bats, is, now you put the case surprising, more especially as the genus of Bats is in N. Zealand very peculiar, & therefore has probably been long introduced, & they now speak of Cretacean fossils there. But the first necessary step has to be shown, namely of a Bat taking to feed on the ground or anyhow & anywhere except in the air: I am bound to confess I do know one single such fact. viz of an Indian species killing frogs.

Observe that in my wretched polar bear case I do show the first step by which conversion into a whale “would be easy”—“would offer no difficulty.”!! So with Seals, I know of no fact showing any the least incipient variation of seals feeding on the shore. Moreover seals wander much: I searched in vain & could not find one case of any species of Seal confined to any island; & hence wanderers would be apt to cross with individuals undergoing any change on an island, as in case of land-birds of Madeira & Bermuda. The same remark applies perhaps even to Bats, as they frequently come to Bermuda from the mainland, though about 600 miles distant.

With respect to the Amblyrhynchus of Galapagos; one may infer as probable, from marine habit being so rare with Saurians & from the terrestrial species being confined to a few central islets, that its progenitor first arrived at the Galapagos; from what country it is impossible to say as its affinity (I believe) is not very close to any known species. The offspring of the terrestrial species was probably rendered marine. Now in this case I do not pretend I can show variation in habits; but we have in the terrestrial species a vegetable feeder (in itself a rather unusual circumstance) largely on lichens, & it would not be a great change for its offspring to feed first on littoral algæ & then on submarine algæ.

I have said what I can in defence; but yours is a good line of attack. We should, however, always remember that no change will ever be effected till a variation in habits or structure or of both chance to occur in right direction so as to give the organism in question an advantage over other already established occupants of land or water; & this may be in any particular case indefinitely long.—   I am very glad you will read my Dogs M.S; for it will be important to me to see what you think of balance of evidence.⁴ After long pondering on a subject it is often hard to judge.—

With hearty thanks for your most interesting letter. Farewell | My dear old Master | C. Darwin

Emma & self wrote a few days ago to you.—