On inference from evidence

TweetThis is not really a question of politics and evoluion, but it interested me, so I shall pass it along... I was reading my friend John Wilkins's blog Evolving Thoughts.

Evolving Thoughts. A great blog written and edited by Dr. John Wilkins.

Today he was considering a letter sent from the nineteenth-century anatomist, "Darwin's Bulldog", Thomas Henry Huxley to the Anglican Priest, amateur naturalist and novelist Charles Kingsley. The letter he quotes I have pasted below (the authorial insertions are John's) :

Thomas Henry Huxley, as portrayed in Vanity Fair

"With respect to the sterility question [between species], I do not think there is much doubt as to the effect of breeding in and in [we would now use the neologism "inbreeding"] in destroying fertility. But the sterility which must be obtained by the selective breeder in order to convert his morphological species into physiological species – such as we have in nature – must be quite irrespective of breeding in and in.
There is no question of breeding in and in between a horse and an ass, and yet their produce is usually a sterile hybrid.
So if Carrier and Tumbler [varieties of pigeon], e.g., were physiological species equivalent to Horse and Ass, their progeny ought to be sterile or semi-sterile. So far as experience has gone, on the contrary, it is perfectly fertile – as fertile as the progeny of Carrier and Carrier or Tumbler and Tumbler.
From the first time that I wrote about Darwin’s book in the Times and the Westminster [Review] until now, it has been obvious to me that this is the weak point of Darwin’s doctrine. He has shown that selective breeding is a vera causa [Whewell's term for a true cause, taken from Newton] for physiological species.
But I entertain little doubt that a carefully devised system of experimentation would produce physiological species by selection – only the feat has not been performed yet."

Charles Kingsley in Vanity Fair

This is a really interesting letter, for many reasons - not least that Huxley is discussing the matter with the Chaplain to the Queen of England! Where John's consideration of this letter takes him to consider the evolution of sterility - an interesting quesiton in evolutioanry biology, what I find interesting abou this letter is what it reveals about the different expectations of a scientific theory that are evident between Huxley's thinking on the one hand, and Darwin's on the other. Notbaly Huxley clearly has the expectation of experimental proof of speciation, and, as he mentions in this letter, had makde this point in his early reviews of Darwin's work. 

Darwin, of course, was - as Michael Ruse has long since demonstrated, - strongly under the influence of the Cambridge philosopher of science, William Whewell, especially when it came to inductive reasoning and the question of what made for a sound explanation in science. In his 1840 work The Philosophy of the Inductive Sciences (1840), Whewell held to what he called the 'concillience of inductions' - ie: the conviction that if the hypothesis expalined enough facts then it was likley to be near the mark, but that if it explained enough facts from different fields and especially if it explained facts that the theory had not been framed to explain, then one could be really confident it was a true explanation, or, a vera causa, as he termed it. - Thus Darwin didn't need to actually see speciation to be convinced he was on the right track, - common ancestry explained so much from so many diverse fields of natural history, and speciation was a logical outcome of this view in light of the present day diversity of life.  Malthus just gave him the 


Cambridge philosopher William Whewell

mechanism, - competition and extinction. The issue of sterility was less of an immediate issue for Darwin, even though he did acknowledge the problem.

Huxley, on the other hand, was much more of the empiricist school of John Stuart Mill, who wrote in the philosophy of science as well as poltical economy. The most convincing - and indeed for Huxley - the necessary evidence had to be observed, and preferably observed under experimental conditions. This was always going to be a problem for him, especially where speciation was concerned -  which left Darwin perplexed. Darwin realised that the geological time involved and the selective nature of the fossil record made it unlikley that speciation would ever be demonstrated to Huxley's criteria.

Kingsley, of course, had written to Darwin on the eve of the publication of Origin to say that he was ready to be convinced. Following Darwin's analogy from domestic animals, he wrote to say that he could readily follow Darwin's line of reasoning from long familiarity with the breeding of dogs and horses - he also added, almost as an after thought that a God who made things make themseleves was a much more noble conception of the deity than a God who had to interfere all the time. It was Kingsley's expression of this last sentiment that Darwin included in the second edition of Origin, suggesting that on such authority there were no grounds for thinking that the views he put forward in the book should offend the religious feelings of anyone.