stylistic:style_transfer, quality:correction, structural:summarization
Natural selection

Huxley was certainly not slavish in his dealings with Darwin. As shown in every biography, they had quite different and rather complementary characters. Important also, Darwin was a field naturalist, but Huxley was an anatomist, so there was a difference in their experience of nature. Lastly, Darwin's views on science were different from Huxley's views. For Darwin, natural selection was the best way to explain evolution because it explained a huge range of natural history facts and observations: it solved problems. Huxley, on the other hand, was an empiricist who trusted what he could see, and some things were not easily seen. With this in mind, one can appreciate the debate between them, Darwin writing his letters, Huxley never going quite so far as to say he thought Darwin was right.

Huxley's reservations on natural selection were of the type "until selection and breeding can be seen to give rise to varieties which are infertile with each other, natural selection cannot be proved". Huxley's position on selection was agnostic; yet he gave no credence to any other theory. Despite this concern about evidence, Huxley saw that if evolution came about through variation, reproduction and selection then other things would also be subject to the same pressures. This included ideas because they are invented, imitated and selected by humans: ‘The struggle for existence holds as much in the intellectual as in the physical world. A theory is a species of thinking, and its right to exist is coextensive with its power of resisting extinction by its rivals.’ This is the same idea as meme theory put forward by Richard Dawkins in 1976.

Darwin's part in the discussion came mostly in letters, as was his wont, along the lines: "The empirical evidence you call for is both impossible in practical terms, and in any event unnecessary. It's the same as asking to see every step in the transformation (or the splitting) of one species into another. My way so many issues are clarified and problems solved; no other theory does nearly so well".

Huxley's reservation, as Helena Cronin has so aptly remarked, was contagious: "it spread itself for years among all kinds of doubters of Darwinism". One reason for this doubt was that comparative anatomy could address the question of descent, but not the question of mechanism.