Seeing Further (24 page)

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 selection
⁸
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:

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:

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:

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:

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 understanding 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.

Darwin never crossed the digital bridge. If he had, he would have had a ready answer to Fleeming (pronounced Fleming) Jenkin, the Scottish engineer who – independently of his colleague Lord Kelvin (with whom he collaborated on the trans-Atlantic cable) – gave Darwin a hard time over matters of theory.
¹¹
Jenkin pointed out that, on the current non-digital,
blending view
of heredity, variation would be swamped by successive sexual crossings, and after a few generations would disappear. There’d be no hereditary variation for natural selection to work on. Blending inheritance would be like mixing black and white paint: you get grey, and no amount of subsequent mixing of grey with grey will give you back the original black and white.

As a matter of fact, any fool could have seen that Jenkin’s premise must be wrong. Variation does not dissolve away as the generations go by. We are not more uniform than our grandparents were, and our grandchildren will retain the same level of variation as we possess. Jenkin thought he was doubting Darwin. Actually he was doubting observable facts. Nevertheless, his criticism worried Darwin.

Enlightened by Mendel’s nineteenth-century peas and building on Hardy and Weinberg’s elementary algebra, the twentieth-century founders of population genetics, R.A. Fisher, J.B.S. Haldane and Sewall Wright, buried Fleeming Jenkin. If genes are countable, digital entities that don’t blend, their frequencies have no inherent tendency to change. If they do change, that is evolution, and it happens for a reason. The most interesting reason is non-random selection, but random drift also occurs – to an extent disputed among the founding fathers but now widely admitted among molecular geneticists. Even those three founding fathers never knew quite how digital genetics really is. In the light of the Watson/Crick revolution, we now see the very genes themselves as digitally coded messages, digital in exactly the same sense – and in the same way to an astonishing level of detail – as computer information is digital.

Of the three founding fathers of population genetics, it was Fisher who, in his great book of 1930,
The Genetical Theory of Natural Selection,
most clearly expressed the evolutionary significance of blending inheritance and its Mendelian antithesis.
¹²
If genes did indeed blend, the variance available for selection would be
halved
in every generation. It’s the grey paint over again, but Fisher proved it mathematically. Mutation rates would have to be colossal – utterly unrealistic – to maintain the variation. Fisher quotes a letter from Darwin to Huxley, tentatively dated to 1857, before
The Origin,
which shows how tantalisingly close Darwin himself came to Mendelism:

Even Fisher didn’t know how breathtakingly near Darwin really was to discovering Mendelian genetics, even working on sweetpeas! In 1867, he wrote a letter to Wallace that began as follows:

That last sentence is a beautiful example of the power of reason, and the importance of seeing through the obvious. When a male mates with a female, you do not get a hermaphrodite. You get either a male or a female, with approximately equal probability. In a way, Mendel never needed to go into his monastery garden. All he had to do was take the inheritance of sex itself, and generalise it to all other cases of inheritance. Digital heredity was staring us in the face, in the most obvious way you could imagine. The trouble was, it was
too
obvious to be noticed. Darwin noticed it, and he came close to making the connection. But, just as Patrick Matthew didn’t quite cross the bridge that Darwin and Wallace crossed, so Darwin didn’t quite manage to cross the Mendel/Fisher Bridge – at least not decisively enough to answer Fleeming Jenkin.

I distinguished Bridge One from Bridge Two as ‘stabilising selection’ versus ‘directional selection’. But there’s more to it than that – or perhaps the distinction I am about to make really separates Matthew’s Bridge Two from Darwin and Wallace’s Bridge Three. I am talking about the distinction between selection as a negative force and selection as a positive, constructive force that puts together complex new ‘designs’. My own preferred way – the ‘selfish gene’ way – of explaining this is again to deploy ‘digital genes’, so perhaps we really have to cross Bridge Five in order to paint the full picture.