OU Lecture 2009: Developing natural selection

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Professor Richard Dawkins discusses Darwin’s peers and the development of the theory of Natural Selection.

By: Professor Richard Dawkins (Guest) , The Darwin web team (Programme and web teams)

  • Duration 10 mins
  • Updated Monday 27th April 2009
  • Introductory level
  • Posted under TV, OU Lecture
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Copyright The Open University

Transcript

I agree with WJ Dempster, Patrick Matthew’s modern champion, that Matthew has been unkindly treated by history. But, unlike Dempster, I hesitate to assign full priority to him. Partly it's because he wrote in a much more obscure style than either Darwin or Wallace, which makes him hard to understand. Darwin himself noted this. But mostly it's because he seems to have underestimated it to an extent where we have to doubt whether he really understood how important it was.

And the same could be said even more strongly - which is why I haven't treated his case in the same detail as Matthews - of WC Wells, whom Darwin also scrupulously acknowledged in the fourth and subsequent editions of The Origin. Wells made the leap to generalise from artificial to natural selection, but he applied it only to humans, and he thought of it as choosing among races of people rather than individuals (as Darwin and Wallace did). Wells then seems to have arrived at a form of group selection, rather than true Darwinian natural selection (as Matthew did) which selects individual organisms for their reproductive success.

And Darwin also lists other partial predecessors who had shadowy inklings of natural selection. Like Patrick Matthew, none of them seems to have grasped the earth-shattering significance of the idea they’d lit upon, and I shall use Matthew’s name to represent them all. I am increasingly inclined to agree with Matthew that natural selection itself scarcely needed discovering. What needed discovering was the significance of natural selection for the evolution of all life.

Alfred Russel Wallace (1823-1913) was different. Although he discovered natural selection later than Patrick Matthew and later than Darwin’s unpublished manuscripts, he has a genuine claim to be up there with Darwin and Newton among the immortals. When Wallace hit upon natural selection, he was in no doubt of its immense importance for the whole history of life. The very title of his paper, the one he sent to Darwin and which set the cat among Darwin’s pigeons says it all: "On the Tendency of Varieties to Depart Indefinitely from the Original Type". "Depart indefinitely" - that was the key phrase. If they departed indefinitely from the original type, they can branch and eventually spawn all of life, and Wallace made that explicit.

The drama of how Wallace’s letter arrived at Down House on the 17th of June 1858, casting Darwin into an agony of indecision and worry, is too well known for me to retell it. In my view, the whole episode is one of the more creditable and agreeable in the history of scientific priority disputes, precisely because it wasn’t a dispute, although it so easily could have become one. It was resolved amicably and with heart-warming generosity on both sides, especially Wallace’s.

As Darwin later wrote: “Early in 1856 Lyell advised me to write out my views pretty fully, and I began at once to do so on a scale three or four times as extensive as that which was afterwards followed by my Origin of Species, yet it was only a abstract of the materials which I had collected, and I had got through about half the work on this scale. But my plans were overthrown, for early in the summer of 1858 Mr Wallace, who was then in the Malay Archipelago, sent me an essay, "On the Tendency of Varieties to Depart Indefinitely from the Original Type", and this essay contained exactly the same theory as mine. Mr Wallace expressed the wish that if I thought well of this essay, I should send it to Lyell for perusal.

The circumstances under which I consented at the request of Lyell and Hooker to allow an extract from my manuscript, together with a letter to Asa Gray, dated September the 5th, 1857, to be published at the same time with Wallace’s essay, are given in the Journal of the Proceedings of the Linnean Society. I was at first very unwilling to consent, as I thought that Mr Wallace might consider my doing so unjustifiable, for I did not then know how generous and noble was his disposition. The extract from my manuscript and the letter to Asa Gray had neither been intended for publication and were badly written.

Mr Wallace’s essay, on the other hand, was admirably expressed and quite clear. Nevertheless, our joint productions excited very little attention, and the only published notice of them which I can remember was by Professor Horton of Dublin whose verdict was that all that was new in them was false and what was true was old. This shows how necessary it is that any new view should be explained at considerable length in order to arouse public attention.”

Darwin was over-modest about his own two papers. Both are models of the explainer’s art. Wallace’s paper is also very clearly argued. His ideas were indeed remarkably similar to Darwin’s, and there’s no doubt at all that Wallace arrived at them independently. In my opinion, the Wallace paper needs to be read in conjunction with his earlier paper in the Annals and Magazine of Natural History.

Darwin read this paper when it came out in 1855 and, in fact, it led to Wallace joining his large circle of correspondents and to Darwin’s engaging Wallace’s services as a collector. But, oddly, Darwin didn’t see in the 1855 paper any warning that Wallace was by then a convinced evolutionist of a very Darwinian stamp. I mean as opposed to the Lamarckian view of evolution which saw modern species as all on a ladder, changing into one another as they moved up the ladder.

By contrast, Wallace, in 1855, had a clear view of evolution as a branching tree, exactly like Darwin’s famous diagram which became the only illustration in The Origin of Species. The 1855 paper, however, makes no mention of natural selection or the struggle for existence. That was left to Wallace’s 1858 paper, the one that hit Darwin like a lightning bolt. Here Wallace even used the phrase "struggle for existence." Wallace devoted considerable attention to the exponential increase in numbers, another key Darwinian point.

Wallace wrote: “The greater or less fecundity of an animal is often considered to be one of the chief causes of its abundance or scarcity. But a consideration of the facts will show us that it really has little or nothing to do with a matter, even the least prolific of animals would increase rapidly if unchecked, whereas it is evident that the animal population of the globe must be stationary or perhaps decreasing.” And Wallace deduced from this that “the numbers that die annually must be immense and as the individual existence of each animal depends upon itself, those that die must be the weakest.”

Wallace’s peroration could have been Darwin himself writing.

“The powerful retractile talons of the falcon and the cat tribes have not been produced or increased by the volition of those animals; but among different varieties which occurred in the earlier and less highly organised forms of these groups, those always survived longest which had the greatest facilities for seizing their prey. Neither did the giraffe acquire its long neck by desiring to reach the foliage of the more lofty shrubs, and constantly stretching its neck for the purpose, but because any varieties which occurred among its antitypes with a longer neck than usual at once secured a fresh range of pasture over the same ground as their shorter-necked companions, and on the first scarcity of food were thereby enabled to outlive them.

"Even the peculiar colours of many animals, especially insects, so closely resembling the soil or the leaves or the trunks on which they habitually reside, are explained on the same principle; for though in the course of ages varieties of many tints may have occurred, yet those races having colours best adapted to concealment from their enemies would inevitably survive the longest. We have also here an acting cause to account for that balance so often observed in nature; a deficiency in one set of organs always being compensated by an increased development of some others, powerful wings accompanying weak feet, or great velocity making up for the absence of defensive weapons.

"For it has been shown that all varieties in which an unbalanced deficiency occurred could not long continue their existence. The action of this principle is exactly like that of the centrifugal governor of the steam engine, which checks and corrects any irregularities almost before they become evident.”

The image of the steam governor is a powerful one which I can’t help feeling Darwin might have envied.

This clip is from the Professor Richard Dawkins lecture given on Tuesday 17th March 2009 at the Natural History Museum, London.

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