As it turned out, he didn't have quite the same view as Darwin. Wallace thought that the main selective pressure came from the struggle to survive in a hostile environment - drought, storm, flood, whatever. It was this struggle that removed unfit creatures from the breeding pool. Darwin had a rather blunter view of the selection mechanism: competition among the organisms themselves. It wasn't quite `Nature red in tooth and claw' as Tennyson had written in his In Memoriam of 1850, but the claws were unsheathed and there was a certain pinkness to the teeth. To Darwin, the environment set a background of limited resources, but it was the creatures themselves that selected each other for the chop when they competed for those resources. Wallace's political leanings made him detect a purpose in natural selection: to `realise the ideal of a perfect man'. Darwin refused even to contemplate this kind of utopian hogwash.
Wallace hadn't mentioned publishing his theory, but Darwin now felt obliged to recommend it to him. At that point it looked as if Charles had compounded his Really Bad idea, but for once the universe was kind. Lyell, searching for a compromise, suggested that the two men might agree to publish their discoveries simultaneously. Darwin was concerned that this might make it look as if he'd pinched Wallace's theory, worried himself to distraction, and finally handed the negotiating over to Lyell and Hooker and washed his hands of it.
Fortunately, Wallace was a true gentleman (the accident of breeding notwithstanding) and he agreed that it would be unfair to Darwin to do anything else. He hadn't realised that Darwin had been working on exactly the same theory for many years, and he had no wish to steal such an eminent scientist's thunder, perish the very thought. Darwin quickly put together a short version of his own work, and Hooker and Lyell got the two papers inserted into the schedule of the Linnaean Society, a relatively new association for natural history. The Society was about to shut up shop for the summer, but the council fitted in an extra meeting at the last minute, and the two papers were duly read to an audience of about thirty fellows.
What did the fellows make of them? The President reported later that 1858 had been a rather dull year, not `marked by any of those striking discoveries which at once revolutionise, so to speak, our department of science'.
No matter. Darwin's fear of controversy was now irrelevant, because the cat was out of the bag, and there was no chance whatsoever that the beast could be stuffed back in. Yet, as it happened, the anticipated controversy didn't quite materialise. The meeting of the Linnaean Society had been rushed, and the fellows had departed muttering vaguely under their breaths, feeling that they ought to be outraged by such blasphemous ideas ... yet puzzled because the enormously respected (and respectable) Hooker and Lyell clearly felt that both papers had some merit.
And the ideas struck home with some. In particular, the VicePresident promptly removed all mention of the fixity of species from a paper he was working on.
Now that Darwin had been forced to put his head above the parapet, he would lose nothing by publishing the book that he had previously decided not to write, but had constantly been thinking about anyway. He had intended it to be a vast, multi-volume treatise with extensive references to scientific literature, examining every aspect of his theory. It was going to be called Natural Selection (a conscious or subconscious reference to Paley's Natural Theology?). But time was pressing. He polished up his existing essay, changing the title to On the Origin of Species and Varieties by Means of Natural Selection. Then, on the insistent advice of his publisher John Murray, he cut out the `and Varieties'. The first print run of 1250 copies went on sale in November 1859. Darwin sent Wallace a complimentary copy, with a note: `God knows what the public will think.'
In the event, the book sold out before publication. Over 1500 advance orders came in for those 1250 copies, and Darwin promptly started working on revisions for a second edition. Charles Kingsley, author of The Water-Babies, country rector, and Christian socialist, loved it, and wrote a lavish letter: `It is just as noble a conception of Deity, to believe that He created primal forms capable of selfdevelopment ... as to believe that He required a fresh act of intervention to supply the lacunas [1] which He himself had made.' Kingsley was something of a maverick, because of his socialist views, so praise from this source was something of a poisoned chalice.
The reviews, steadfast in their Christian orthodoxy, were distinctly less favourable. Even though Origin hardly mentions humanity, all the usual complaints about men and monkeys, and insults to God and His Church, were trotted out. What particularly galled the reviewers was that ordinary people were buying the thing. It was all right for the upper classes to toy with radical views, it had an attractive frisson of naughtiness and was perfectly harmless among gentlemen of breeding, though not ladies of course; but those same views might put ideas into the common folk's heads, if they were exposed to them, and upset the established order. For Heaven's sake, the book was even selling to commuters outside Waterloo railway station! It must be suppressed!
[1] No, not long-haired South American beasts of burden, but Latin for `gaps'.
Too late. Murray geared up to print 3000 copies of the second edition, whose likely sales were not going to suffer from public controversy. And the people who mattered most to Darwin - Lyell, Hooker, and the anti-religious `evangelist' Thomas Henry Huxley - were impressed, and pretty much convinced. While Charles stayed out of the public debate, Huxley set to with a will. He was determined to advance the cause of atheism, and Origin gave him a point of leverage. The radical atheists loved the book, of course: its overall message and scientific weightiness were enough for them, and they weren't too concerned about fine points. Hewett Watson declared Darwin to be `the greatest revolutionist in natural history of this century'.
In the introduction to Origin, Darwin begins by telling his readers the background to his discovery:
When on board H.M.S. Beagle, as naturalist, I was much struck with certain facts, in the distribution of the inhabitants of South America, and in the geological relations of the present to the past inhabitants of that continent. These facts seemed to me to throw some light on the origin of species - that mystery of mysteries, as it has been called by one of our greatest philosophers. On my return home, it occurred to me, in 1837, that something might perhaps be made out of this question by patiently accumulating and reflecting on all sorts of facts which could possibly have any bearing on it.
Apologising profusely for lack of space, and time, to write something more comprehensive than his 150,000-word tome, Darwin then moves towards a short summary of his main idea. Writers on science generally appreciate that it is seldom enough to discuss the answer to a question: it is also necessary to explain the question. And that, of course, should be done first. Otherwise your readers will not appreciate the context into which the answer fits. Darwin was clearly aware of this principle, so he begins by pointing out that:
It is quite conceivable that a naturalist, reflecting on the mutual affinities of organic beings, on their embryological relations, their geographical distribution, geological succession, and other such facts, might come to the conclusion that each species had not been independently created, but had descended, like varieties, from other species. Nevertheless such a conclusion, even if well founded, would be unsatisfactory, until it could be shown how innumerable species inhabiting this world have been modified, so as to acquire those perfections of structure and coadaptation which most justly excites our admiration.
Already we see a gesture towards Paley - 'perfections of structure' is a clear reference to the watch/watchmaker argument, and `had not been independently created' shows that Darwin doesn't buy Paley's conclusion. But we also see something that characterises the whole of Origin: Darwin's willingness to acknowledge difficulties in his theory. Time and again he raises possible objections - not as straw men, to be knocked flat again, but as serious points to be considered. More than once he concludes that there is more to be learned, before the objection can be resolved. Paley, to his credit, did some
thing similar, though he didn't go as far as admitting ignorance: he knew that he was right. Darwin, a real scientist, not only had his doubts - he shared them with his readers. He would not have arrived at his theory to begin with if he had failed to seek the weaknesses of the hypotheses upon which it was based.
He also, of course, makes it clear what his own work is adding to the speculations of earlier 'transmutationists'. Namely: he has come up with a mechanism for species change. There are advantages in being honest about ,your own limitations: you gain the right to talk about the limitations of others. And now he tells us what that
mechanism is. Species, we know, are variable - the domestication of wild species like chickens, cows, and dogs is clear evidence of that. Although that is deliberate selection by humans, it opens the door to selection by nature without human aid:
I will then pass on to the variability of species in a state of nature ... We shall, however, be enabled to discuss what circumstances are most favourable to variation. In the next chapter the Struggle for Existence amongst all organic beings throughout the world, which inevitably follows from their high geometrical powers of increase, will be treated of ... The fundamental subject of Natural Selection will be treated at some length in the fourth chapter; and we shall then see how Natural Selection almost inevitably causes much Extinction of the less improved forms of life, and induces what I have called Divergence of Character.
He then promises four chapters on `the most apparent and gravest difficulties of the theory', prominent among these being to understand how a simple organism or organ can change into a highly complex one - another nod to Paley. The introduction ends with a flourish:
I can entertain no doubt ... that the view which most naturalists entertain, and which I formerly entertained - namely, that each species has been independently created - is erroneous. I am fully convinced that species are not immutable; but that those belonging to what are called the same genera are lineal descendent of some other and generally extinct species ... Furthermore, I am convinced that Natural Selection has been the main but not exclusive means of modification.
In essence, Darwin's theory of natural selection, which soon became known as evolution,[1] is straightforward. Most people think they
[1] The term was around in Victorian times, as a phenomenon but not a specific mechanism. Darwin didn't use it in Origin, nor in the later The Descent of Man. However, the final word in Origin is 'evolved'.
understand it, but its simplicity is deceptive, and its subtleties are easily underestimated. Many of the standard criticisms of evolutionary theory stem from common misunderstandings, not from what the theory actually proposes. The ongoing scientific debate about details is often misrepresented as disagreement with the general outline, which is an error based on too simple-minded a view of how science develops and what `knowledge' is.
Briefly, Darwin's theory goes like this.
1. Organisms, even those in the same species, are variable. Some are bigger than others, or bolder than others, or prettier than others.
2. This variability is to some extent hereditary, passed on to offspring.
3. Unchecked population growth would quickly exhaust the capacity of the planet, so something checks it: competition for limited resources.
4. Therefore as time passes, the organisms that do survive long enough to breed will be modified in ways that improve their chance of surviving to breed, a process called natural selection.
5. Ongoing slow changes can lead, in the long run, to big differences.
6. The long run has been very long indeed - hundreds of millions of years, maybe more. So by now those differences can have become huge.
It's relatively simple to put these six ingredients together and deduce that new species can arise without divine intervention - provided we can justify each ingredient.
Even though different species seem to stay pretty much the same - think lions, tigers, elephants, hippos, whatever - it is actually rather obvious that, in general, species are not fixed for all time. The changes are relatively slow, which is why we don't notice them. But they do happen. We've already seen that in Darwin's finches, evolutionary changes can be and have been observed on a timescale of years, and in bacteria they occur on a timescale of days.
The most obvious evidence for the variability of species, in Darwin's day and ours, was the domestication of animals - sheep, cows, pigs, chickens, dogs, cats ...
... and pigeons. Darwin was rather knowledgeable about pigeons, he belonged to two London pigeon clubs. Every pigeon-fancier knows that by selectively breeding particular combinations of male and female pigeons, it is possible to produce `varieties' of pigeons with particular characteristics. `The diversity of the breeds is something astonishing,' says Darwin in the first chapter of Origin. The English carrier pigeon has a wide mouth, large nostrils, elongated eyelids, a long beak. The short-faced tumbler has a short stubby beak like a finch. The common tumbler flies high up in a tightly knit flock, and has an odd habit of falling about in the sky, whence its name. The runt (despite its name) is huge, with a long beak and large feet. The barb is like the carrier but with a short, broad beak. The pouter has an inflatable crop and can puff out its chest. The turbit has a short beak and a line of reversed feathers on its chest. The Jacobin has so many reversed feathers on its neck that they form a hood. Then there are the trumpeter, laugher, fantail ... These are not separate species: they can interbreed, to produce viable `hybrids' - cross-breeds.
The enormous variety of dogs is so well known that we don't even need to mention examples. It's not that the dog species is exceptionally malleable, just that dog-breeders have been unusually active and imaginative. There is a dog for every purpose that a dog can carry out. Again, they're all dogs, not new (albeit related) species. They can mostly (barring really big size differences) interbreed, and artificial insemination can take care of mere size. Dog sperm plus dog egg makes fertile dog zygote, and, eventually, dog - independently of breed. That's why pedigree pooches need a pedigree, to guarantee that their parentage is pure. If the different varieties of dog were different species, that wouldn't be necessary.
In modem times, it has become clear that cats are just as malleable, but the cat-breeders have only just got going on exotic cats. The same goes for cows, pigs, goats, sheep ... and what about flowers? The number of varieties of garden flowers is immense.
By avoiding the creation of hybrids, the breeder can maintain the individual varieties over many generations. Pouter pigeons breed with pouters to produce (a substantial proportion of) pouters. Carriers mated with carriers produce (mostly) carriers. The underlying genetics, about which Darwin and his contemporaries knew nothing, is complicated enough that apparent hybrids can sometimes arise from what seems to be pure stock, just as two brown-eyed parents can nonetheless have a blue-eyed child. So pigeon-breeders have to eliminate the hybrids.
The existence of these cross-bred varieties does not, of itself, explain how new species can arise of their own accord. Varieties are not species; moreover, the guiding hand of the breeder is evident. But varieties do make it clear that there must be plenty of variability within a species. In fact, the variability is so great that one can readily imagine selective breeding leading to entirely new species, given enough time. And the avoidance of hybrids can maintain varieties from one generation to the next, so their characters (biologese for the features that distinguish them) are heritable (biologese for `able to be passed from one generation to the next'). So Darwin has his first ingredient: heritable variability.
The next ingredient was easier (though still controversial in some quarters). It was time. Oodles and oodles of time, the Deep Time of geologists. Not a few thousand years, but millions, tens of millions ... billions, in fact, though that was further than the Victorians were willing to go. Deep Time, as we've previously observed, is contrary to the biblical chronology of Bishop Ussher, which is why the idea remains controversial among certain Christian fundamentalists, who have
bizarrely chosen to fight their corner on the weakest of grounds, completely needlessly. Deep Time is supported by so much evidence that a truly committed fundamentalist has to believe that his God is deliberately trying to fool him. Worse, if we can't trust the evidence of our own eyes, then we can't trust the apparent element of `design' in living creatures either. We can't trust anything.
Lyell realised that the age of the Earth must be many millions of years, when he looked at sedimentary rocks. These are rocks like limestone or sandstone which form in layers, and have been deposited either underwater, as muddy sediments, or in deserts, as accumulating sand. (Independent evidence for these processes comes from the fossils found in such rocks.) By studying the rate at which modern sediments accumulate, and comparing that with the thickness of known beds of sedimentary rock, Lyell could estimate the time it had taken for the layers of rock to be deposited. Something in the range 1000-10,000 years would produce a layer about a metre thick. But the chalk cliffs of the south coast, around Dover, are hundreds of metres thick. So that's several hundred thousand years of deposition, and we've only dealt with one of the numerous layers of rock that make up the geological column - the historical sequence of different rocks.
We now have many other kinds of evidence for the great age of our planet. The rate of decay of radioactive elements, which we can measure today and extrapolate backwards, is in general agreement with the evidence of the rock layers. The rate of movement of the continents, when combined with the distances they have moved, is again consistent with other estimates. We've seen that India was once attached to Africa, but about 200 million years ago it broke off, and by 40 million years ago it had moved all the way to its current position, butting up against Asia and pushing up the Himalayas.
Darwin's Watch Page 15