Evolution
Lyell initially accepted the conventional view of other men of science, that the fossil record indicated a directional geohistory in which species went extinct. Around 1826, when he was on circuit, he read Lamarck's Zoological Philosophy and on 2 March 1827 wrote to Mantell, expressing admiration, but cautioning that he read it "rather as I hear an advocate on the wrong side, to know what can be made of the case in good hands".:
I devoured Lamarck... his theories delighted me... I am glad that he has been courageous enough and logical enough to admit that his argument, if pushed as far as it must go, if worth anything, would prove that men may have come from the Ourang-Outang. But after all, what changes species may really undergo!... That the earth is quite as old as he supposes, has long been my creed...
He struggled with the implications for human dignity, and later in 1827 wrote private notes on Lamarck's ideas. Lyell reconciled transmutation of species with natural theology by suggesting that it would be as much a "remarkable manifestation of creative Power" as creating each species separately. He countered Lamarck's views by rejecting continued cooling of the earth in favour of "a fluctuating cycle", a long-term steady-state geohistory as proposed by James Hutton. The fragmentary fossil record already showed "a high class of fishes, close to reptiles" in the Carboniferous period which he called "the first Zoological era", and quadrupeds could also have existed then. In November 1827, after William Broderip found a Middle Jurassic fossil of the early mammal Didelphis, Lyell told his father that "There was everything but man even as far back as the Oolite." Lyell inaccurately portrayed Lamarckism as a response to the fossil record, and said it was falsified by a lack of progress. He said in the second volume of Principles that the occurrence of this one fossil of the higher mammalia "in these ancient strata, is as fatal to the theory of successive development, as if several hundreds had been discovered."
In the first edition of Principles, the first volume briefly set out Lyell's concept of a steady state with no real progression of fossils. The sole exception was the advent of humanity, with no great physical distinction from animals, but with absolutely unique intellectual and moral qualities. The second volume dismissed Lamarck's claims of animal forms arising from habits, continuous spontaneous generation of new life, and man having evolved from lower forms. Lyell explicitly rejected Lamarck's concept of transmutation of species, drawing on Cuvier's arguments, and concluded that species had been created with stable attributes. He discussed the geographical distribution of plants and animals, and proposed that every species of plant or animal was descended from a pair or individual, originated in response to differing external conditions. Species would regularly go extinct, in a "struggle for existence" between hybrids, or a "war one with another" due to population pressure. He was vague about how replacement species formed, portraying this as an infrequent occurrence which could rarely be observed.
The leading man of science Sir John Herschel wrote from Cape Town on 20 February 1836, thanking Lyell for sending a copy of Principles and praising the book as opening a way for bold speculation on "that mystery of mysteries, the replacement of extinct species by others" – by analogy with other intermediate causes, "the origination of fresh species, could it ever come under our cognizance, would be found to be a natural in contradistinction to a miraculous process". Lyell replied: "In regard to the origination of new species, I am very glad to find that you think it probable that it may be carried on through the intervention of intermediate causes. I left this rather to be inferred, not thinking it worth while to offend a certain class of persons by embodying in words what would only be a speculation."
Whewell subsequently questioned this topic, and in March 1837 Lyell told him:
If I had stated... the possibility of the introduction or origination of fresh species being a natural, in contradistinction to a miraculous process, I should have raised a host of prejudices against me, which are unfortunately opposed at every step to any philosopher who attempts to address the public on these mysterious subjects ...
As a result of his letters and, no doubt, personal conversations, Huxley and Ernst Haeckel were convinced that, at the time he wrote Principles, he believed new species had arisen by natural methods. Adam Sedgwick wrote worried letters to him about this.
By the time Darwin returned from the Beagle survey expedition in 1836, he had begun to doubt Lyell's ideas about the permanence of species. He continued to be a close personal friend, and Lyell was one of the first scientists to support On the Origin of Species, though he did not subscribe to all its contents. Lyell was also a friend of Darwin's closest colleagues, Joseph Dalton Hooker and Huxley, but unlike them he struggled to square his religious beliefs with evolution. This inner struggle has been much commented on. He had particular difficulty in believing in natural selection as the main motive force in evolution.
Lyell and Hooker were instrumental in arranging the peaceful co-publication of the theory of natural selection by Darwin and Alfred Russel Wallace in 1858: each had arrived at the theory independently. Lyell's views on gradual change and the power of a long time scale were important because Darwin thought that populations of an organism changed very slowly.
Although Lyell rejected evolution at the time of writing the Principles, after the Darwin–Wallace papers and the Origin Lyell wrote in one of his notebooks on 3 May 1860:
Mr. Darwin has written a work which will constitute an era in geology & natural history to show that... the descendants of common parents may become in the course of ages so unlike each other as to be entitled to rank as a distinct species, from each other or from some of their progenitors ...
Lyell's acceptance of natural selection, Darwin's proposed mechanism for evolution, was equivocal, and came in the tenth edition of Principles. The Antiquity of Man (published in early February 1863, just before Huxley's Evidence as to Man's Place in Nature) drew these comments from Darwin to Huxley: "I am fearfully disappointed at Lyell's excessive caution" and "The book is a mere 'digest'".Quite strong remarks: no doubt Darwin resented Lyell's repeated suggestion that he owed a lot to Lamarck, whom he (Darwin) had always specifically rejected. Darwin's daughter Henrietta (Etty) wrote to her father: "Is it fair that Lyell always calls your theory a modification of Lamarck's?"
In other respects Antiquity was a success. It sold well, and it "shattered the tacit agreement that mankind should be the sole preserve of theologians and historians". But when Lyell wrote that it remained a profound mystery how the huge gulf between man and beast could be bridged, Darwin wrote "Oh!" in the margin of his copy.
