Historians of science have raised the suggestion that Wallace’s version of natural selection was not quite so Darwinian as Darwin himself believed. Wallace persistently used the word "variety" as the level of entity at which natural selection acts, and there was an example in this long passage I just read, an example of Wallace’s using the word "race’" in a similar sense. Some people have suggested that Wallace, unlike Darwin, who clearly saw selection as choosing among individuals, was proposing what nearly all modern theorists rightly denigrate as group selection.
This would be true if by "varieties" or "races" Wallace meant geographically separated groups of individuals or races in the more usual sense of the word. At first, I wondered myself whether Wallace meant that. But a careful reading of his paper rules it out. By "variety" and "race", Wallace meant what we would nowadays call genetic type, even what a modern population geneticist might mean by an allele. To Wallace, in this paper, "variety" meant not a local race of eagles, for example, but that set of individual eagles whose talons, say, were hereditarily sharper than usual.
If I'm right, it's a similar misunderstanding to the one suffered rather grievously by Darwin whose use of the word "race" in the subtitle of The Origin of Species is all too often misread as supporting group selection or even racialism. That subtitle or rather alternative title is "the preservation of favoured races in the struggle for life".
Once again, Darwin was using "race" to mean that set of individuals who share a particular hereditary characteristic such as sharp talons, not a geographically distinct race such as the hooded crow. If he had meant that, Darwin too would have been guilty of the group selection confusion. I believe that neither Darwin nor Wallace was, and by the same token, I do not believe that Wallace’s conception of natural selection was different from Darwin’s.
I should add, by the way, that Darwin did countenance a form of group selection on one occasion when discussing the evolution of co-operation in humans. I think that was the only occasion.
As for the calumny that Darwin plagiarised Wallace, that’s rubbish. The evidence is very clear that Darwin did think of natural selection before Wallace, although he didn’t publish it. We have his abstract of 1842, his longer essay of 1844, both of which establish his priority clearly, as did his letter to Asa Gray of 1857, read at the Linnean Society in 1858.
Why Darwin delayed so long before publishing is one of the great mysteries in the history of science. Some historians have suggested that he was afraid of the religious implications, others the political ones. Perhaps he was afraid of upsetting his devout wife. Maybe he was just a perfectionist keen to have all his evidence lined up and in place before going public. Or did he just get distracted by barnacles?
When Wallace’s letter arrived, Darwin was more surprised than we moderns might think he had any right to be. He wrote to Lyell: “I never saw a more striking coincidence. If Wallace had had my manuscript sketch written out in 1842, he could not have made a better short abstract of it. Even his terms now stand as heads of my chapters.”
The coincidence extended to both Darwin and Wallace being inspired by Thomas Malthus on population. Darwin, by his own account, was immediately struck by Malthus’ emphasis on overpopulation and competition. He wrote in his autobiography: “In October 1838, that is fifteen months after I had begun my systematic enquiry, I happened to read for amusement Malthus on population, and being well prepared to appreciate the struggle for existence which everywhere goes on from long continuous observation of the habits of animals and plants, it at once struck me that under these circumstances favourable variations would tend to be preserved and unfavourable ones to be destroyed. The result of this would be the formation of new species. Here then I had at last got a theory by which to work.”
Wallace’s epiphany after reading Malthus took longer to happen but was more dramatic when it came to his overheated brain in the midst of a malarial fever on the Island of Ternata in the Moluccas Archipelago.
“I was suffering from a sharp attack of intermittent fever, and every day during the cold and succeeding hot fits had to lie down for several hours, during which time I had nothing to do but to think over any subjects then particularly interesting me. One day something brought to my recollection Malthus’ principles of population. I thought of his clear exposition of the positive checks to increase, disease, accidents, war and famine which keep down the population of savage races to so much lower on average than that of more civilised peoples. It then occurred to me…” and Wallace proceeds to his own admirably clear exposition of natural selection as the guiding principle of all evolution.
I want to recognise four bridges to evolutionary understanding, and I can illustrate them with our four claimants to independent discovery of natural selection. Blyth crossed the first of Darwin’s four bridges, Matthew the first two, Wallace the first three and Darwin all four.
The first bridge is to natural selection as a force for weeding out the unfit. I’ve used Blyth as my example of a 19th century writer who crossed this bridge, but really the only reason to single him out is that he has been championed by Loren Eisely as a predecessor and even a possible source of Darwin’s ideas. As Stephen Gould has argued, however, the idea of natural selection as a weeder out, a purely negative force, was already widespread.
“Yes, Blyth had discussed natural selection but Eisely didn’t realise, thus committing the usual and fateful error in this common line of argument, that all good biologists did so in the generations before Darwin. Natural selection ranked as a standard item in biological discourse but with a crucial difference from Darwin’s version. The usual interpretation invoked natural selection as part of a larger argument for created permanency. Natural selection in this negative formulation acted only to preserve the type constant and inviolate by eliminating extreme variants and unfit individuals who threaten to degrade the essence of created form.”
Gould even quotes William Paley himself as setting out this purely negative version of natural selection. As I remarked before, it's almost an anti-evolution argument, for it uses natural selection to explain the fixity of species rather than their changing into other species.
Darwin’s second bridge is the recognition that natural selection can drive evolutionary change. In modern jargon, it amounts to the difference between stabilising selection and directional selection. Matthew, Wallace and Darwin all crossed this second bridge.
Bridge number three leads to the imaginative grasp of the importance of natural selection in explaining all of life, in all of its speciose richness and especially to dispel the illusion of design. Wallace and Darwin certainly crossed it, maybe Matthew did too, but I’ve given reasons for doubting that he developed the full imaginative vision of the "constructive power" of Darwinism, as Wallace in a generous gesture was later to dub it.
Bridge four is the bridge to public understanding and appreciation. Darwin crossed it alone in 1859 by writing The Origin of Species. It's a striking fact, remarked by Darwin himself among others, that when the Darwin/Wallace papers were read to the Linnean Society in 1858, nobody took a blind bit of notice, even among the professional biologists of that august body. The end of year clanger of the hapless President of the Linnean, Thomas Bell, has become notorious and will ring on down the ages.
In his review of the Society’s transactions during 1858 he said that “the year had not been marked by any of those striking discoveries which at once revolutionise the Department of Science on which they bear.” The end of 1859 would have to be reviewed very differently.
The Origin of Species struck the Victorian solar plexus like a steam hammer. The world of the mind would never be the same again, neither science nor anthropology, psychology, sociology, even - and here we come close to the dark side - politics. This book, which Darwin always described as the abstract of the great book that he intended to write but never completed, achieved what the 1858 papers did not.
It isn't that The Origin explained the theory particularly more clearly than Darwin’s and Wallace’s brief offerings of 1858. The difference was that a book length treatment was required to muster all the evidence and lay it out for all to see. One long argument, as Darwin himself called it. And I quoted before Darwin’s own recognition when the joint papers of 1858 fell flat, that “this shows how necessary it is that any new view should be explained at considerable length in order to arouse public attention.”
And is there a fifth bridge which Darwin himself never crossed? Inevitably, a hundred and fifty years later, there are several, but the one that I shall single out is the bridge to the so-called Neo-Darwinism of the modern synthesis. Neo-Darwinism is a union of Darwinian evolution with Mendelian genetics. But the trouble with a word like "neo" is that what is "neo" changes all the time. What comes after nouvelle vague? We don’t want to get into a sort of infinite progress in the way that modernism gives rise to postmodernism and then neo-postmodernism and then what? I shall rename neo-Darwinism, digital-Darwinism.
There may be other things more "neo" than the neo-Darwinian modern synthesis of the 1930s, but digital-Darwinism is here to stay. The essence of Mendelian genetics is that it is digital. Mendelian genes are all or none, they don’t blend. Genes are things you can count in a population’s gene pool. Evolution consists of changing frequencies, of discrete digital countable entities. Not of changing quantities of substances or changing measurements of dimensions. Changing quantities and measurements apply at the organism level but not at the gene level. What happens in natural selection is that successful genes become more frequent in the gene pool and unsuccessful genes become less frequent - frequent as in counted.
This clip is from the Professor Richard Dawkins lecture given on Tuesday 17th March 2009 at the Natural History Museum, London.