by Bill Bryson
With hindsight, we may be tempted to sympathise. But where Huxley, on closing The Origin, movingly sighed, ‘How extremely stupid of me not to have thought of that’, Matthew’s response would seem to have been the Victorian equivalent of ‘Big deal. So what else is new?’ Is this the response of a man who, seven years before Darwin and twenty-seven before Wallace, found himself in possession of the central, unifying idea that dominates all biology and explains almost everything about life?
As a fair parallel, imagine that a seventeenth-century ancestor of Patrick Matthew saw an apple fall (perhaps in the very same orchard, for the Matthews had been farming in the Carse of Gowrie since the sixteenth century). Our earlier Matthew, I imagine to have been a physicist and, as he watched his apple fall, he conjectured that the Earth exerted an attractive force on apples, pulling them towards it. If this hypothetical horticulturalist had later written to Isaac Newton and indignantly claimed priority for the theory of gravitation, Newton (a less generous man than Darwin) would rightly have given him short shrift. The physicist Matthew, let’s suppose, confined his theory to apples, or at best to objects falling towards the Earth. He lacked Newton’s grand vision of the same force acting throughout the universe, responsible for the elliptical orbits of the planets, for the stars in their courses, ultimately for the very structure of the universe itself.
I agree with W.J. Dempster, Patrick Matthew’s modern champion, that Matthew has been unkindly treated by history.6 ‘But, unlike Dempster, I hesitate to assign full priority to him. Partly, it is because he wrote in a much more obscure style than either Darwin or Wallace, which makes it hard to know in some places what he was trying to say (Darwin himself noted this). But mostly it is because he seems to have underestimated the idea, to an extent where we have to doubt whether he really understood how important it was. The same could be said, even more strongly (which is why I have not treated his case in the same detail as Matthew’s), of W.C. 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 therefore 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. 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 had 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 after Matthew (and after Darwin’s unpublished manuscripts) he has a genuine claim to be up there with Darwin and Newton, among the immortals.7 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 depart indefinitely from the original type, they can branch and eventually spawn all of life. And Wallace made that explicit in his paper.
The drama of how Wallace’s letter arrived at Down House on 17 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 heartwarming 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 in my Origin of Species; yet it was only an abstract of the materials which I had collected, and I 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 his essay, I should send it to Lyell for perusal.
The circumstances under which I consented at the request of Lyell and Hooker to allow of an extract from my MS., together with a letter to Asa Gray, dated September 5, 1857, to be published at the same time with Wallace’s Essay, are given in the Journal of the Proceedings of the Linnean Society, 1858, p. 45. I was at first very unwilling to consent, as I thought 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 MS. 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 Haughton 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 is no doubt 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. Indeed, it led to Wallace joining his large circle of correspondents, and to his engaging Wallace’s services as a collector. But, oddly, Darwin did not 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 the 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.
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 the 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 occur
red 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.
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. There was an example in the long passage I have just quoted, and also an example of Wallace’s usage of the word ‘race’ in a similar sense. Some 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 indeed 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 were hereditarily sharper than usual’.
If I am right, it is a similar misunderstanding to the one suffered by Darwin, whose use of the word ‘race’ in the subtitle of The Origin of Species is sometimes misread as supporting group selection8 or even racialism. That subtitle, or alternative title rather, 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.9 And, by the same token, I do not believe that Wallace’s conception of natural selection was different from Darwin’s.
As for the calumny that Darwin plagiarised Wallace, that is rubbish. The evidence is very clear that Darwin did think of natural selection before Wallace, although he did not publish it. We have his abstract of 1842 and his longer essay of 1844, both of which establish his priority clearly, as did his letter to Asa Gray of 1857, which was 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 Robert Malthus on population. Darwin, by his own account, was immediately inspired 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 inquiry, 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 Ternate 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 an 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 conveniently 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. Bridge One is to natural selection as a force for weeding out the unfit. I have used Blyth as my example of a nineteenth-century writer who crossed this bridge, but really the only reason to single him out is that he has been championed by Loren Eiseley as a predecessor, and even a possible source, of Darwin’s ideas. As Stephen Jay 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 Eiseley 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 threatened to degrade the essence of created form.10
Gould even quotes William Paley himself as setting out this purely negative version of natural selection. As I remarked above, it is almost an anti-evolution argument, for it uses natural selection to explain the fixity of species rather than their changing into other species.
Bridge Two 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 Three leads to the imaginative grasp of the importance of natural selection in explaining all of life, in all its speciose richness, and especially to dispel the illusion of design. Wallace and Darwin certainly crossed it. Maybe Matthew did too, but I have 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 understan
ding and appreciation. Darwin crossed it alone, in 1859, by writing The Origin of Species. It is a striking fact, remarked by Darwin himself, 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, so to speak, 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 more clearly than Darwin’s and indeed 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 above 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, 150 years later, there are several, but the one 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 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 way to ‘post-modernism’ and then neo-post-modernism’ 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, and 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 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.