LITMIR.BIZ

Скачать книгу

that integration and harmony always imply a mastermind creator or a team working closely together with oversight of the whole process of manufacture. But as watches and automobile factories were in their time unknown, no one was around to present to them the argument that such complex and well-functioning things can’t make themselves or appear by chance. If they had been confronted with such arguments, they might have insisted that a watch or a factory could arise through the chance combination of atoms. But I suspect they would have had to agree that it is probably impossible for a watch or a factory to assemble by chance. For this to happen, the various components would have to stick together and start to interact in just the right way. And to imagine a fly or a mouse or an elephant coming to be in this way strains credulity too far. Isn’t this like expecting (as 20th-century critics of evolutionary theory used to argue) monkeys with typewriters to produce the plays of Shakespeare?

      This was a stumbling block that seemed to give the advantage to Creationism.

      I can well understand that a person brought up on the Genesis story of the creation of the universe in seven days and sitting in the classroom listening to a lecture on how Darwin discovered the theory of evolution by natural selection would be sceptical about his supposed achievement. Such a person might reasonably wonder: how could just one scientist in the 19th century looking at finch beaks in the Galapagos, and talking to pigeon breeders in England, prove that we evolved over hundreds of millions of years from apes and monkeys, which in turn evolved from something like fish and worms?

      Even if you favour the Darwinian view over the Genesis story, it is good to remember that, on the face of it, it is somewhat implausible. But conversely, if you find Darwinism implausible, it is helpful to stop thinking of Darwin as suddenly and single-handedly coming up with a new and startling theory for which there is still no conclusive evidence. You can think of him instead as one of a long line of thinkers familiar with Epicurean philosophy who found the way over its major stumbling blocks where the theory of natural selection was concerned.

Darwin’s Upgrade: How Selection Causes Evolution

      Lucretius’s claim that nature had experimented with unsuccessful animal species that lacked the right structure to maintain themselves and reproduce was well known to the 18th- and early-19th-century theorists with whom Darwin was familiar. (One of them was his own grandfather, Erasmus Darwin, the author of a long poem on the origins and evolution of life). The early, hostile reviews of On the Origin of Species all mentioned its relationship with the Lucretian text. One reviewer complained, for example, that there was nothing new in Darwin’s ‘speculative’ cosmogony. ‘It is at least as old,’ he said, ‘as Democritus and Epicurus, and has never been presented with more poetic beauty than by Lucretius.’

      Darwin did not attach his own account to Epicureanism, and especially to Lucretius’s version, for obvious reasons. First, Lucretius (and grandfather Darwin) were notorious atheists, and Darwin kept or tried to keep his sceptical views on religion to himself. Second, he had to fend off the charge that his theory of evolution was a poetic fantasy or mere speculation. What, then, was he able to add to (and subtract from) the Epicurean theory that plants and animals evolved ‘by chance’ that changed its status in his mind and eventually in the minds of his early followers? How did Darwinism go beyond speculation to develop into an accepted account of the origin of the various species?

By the time the 19th century rolled around, most naturalists were doubtful that the astonishing number of different species then identified – far too many to have fitted on the Ark – including hundreds of different species of beetles, had been created by twos and on purpose. The true age of the earth had been calculated, and the former existence of the dinosaurs and the giant mammals that had once roamed Europe and Asia was generally known. Two scientific developments transformed the Epicurean theory of the natural origins of plants and animals from a somewhat implausible speculation to a well-founded scientific hypothesis. These were: the cell theory, and the notion of ‘variation’ from generation to generation.

      The discovery, based on the microscope, unavailable to ancient philosophers, that all plants and animals were combinations of individual living cells, and that some cells were free-living animals like the amoeba, made it possible to think of the origins of life in terms of the first appearance of a living cell. To imagine, as Epicureanism required, an elephant emerging from a combination of atoms or even from an atomic seed in the earth was far more difficult than imagining a few single cells forming by chance and later joining up into larger cellular units.

      Another obstacle for the Epicurean theory was the assumption that animals always gave birth to animals like themselves. This seemed obvious to them. Cows did not give birth to sheep, or blackbirds to swallows. This meant that they had to stick to their theory that the original prototypes of every sort of animal had sprung by chance from the earth. Although they fancied that not all of these animal types had been capable of survival and reproduction, they could not envision the descent of one kind of bird or mammal from an entirely different kind of bird or mammal.

Darwin’s breakthrough occurred when he reflected on the selective breeding farmers had carried on for millennia, choosing from the pack or flock or herd, and breeding together male and female dogs, sheep and cattle with desired characteristics. He knew that within the group, individuals varied in their qualities and that offspring were not exactly like their parents. To the idea of variation, he was able to apply the Epicurean idea of selection – success or failure in living and reproducing.

      For Darwin, nature, acting unconsciously, rather than the breeder acting with intention, did the selecting when the resources needed for life were limited and predation was the rule. Animals ate and sometimes killed plants and killed and ate one another. Bacteria, fungi and poisonous plants killed animals. Plants derived nutrition from decomposing animals. Naturalists had long wondered why, if the world was created by a supremely benevolent and skilled craftsman, this was how things worked. They also wondered why trees produced so many useless seeds and short-lived seedlings; why humans produced such an oversupply of ‘spermatic animals’; and why so many children died in infancy. The grim truth was that competition for life was intense. Many individuals of a given species would starve, be eaten or die of accidents before reproducing, or fail to find or attract mates. Darwin argued that the appearance of entirely new species was the result of thousands or millions of generations of variation and selection in changing environments. The temporary stability that the Epicureans had ascribed to the world, which they saw as constantly evolving as the atoms fell into new combinations, was a feature of the individual species as well, and the mortality of the individual person applied to the whole species, whose eventual extinction was similarly inevitable.

Darwin’s contribution, to my mind, was not just to think out how natural selection might work, but to show that it could be considered a lawful process rather than one based entirely on chance. For the constantly repeated accusation against the ancient Epicureans was that the beauty, intricacy and functionality of the many forms of life could not arise from the random motions of atoms. But, in Darwin’s view, the breeder who seeks to improve his or her flock of sheep or hunting dogs, or the pigeon fancier who presents his or her fluffy tailed or brightly feathered specimens to other fanciers, is employing a technology, and wherever a technology is successful, there we expect to find laws of nature. Nature, too, must be employing a technology to create the succession of living forms of the past near 4 billion years.

      To be sure, nature is not aiming to improve any individual species or the livestock or biomass of the planet itself. She is not trying to make animals or entire species faster, smarter or more beautiful. In fact, nature is not trying to do anything. But she mercilessly eliminates some members of each species who aren’t keeping up with the others in producing, and in some cases raising to maturity, offspring who will have their own offspring. As a result, the face of living nature changes in ways we can often explain. Species have appeared and disappeared over the eons, and for this to have happened, there must be laws of nature underlying these changes. Chance – or what we think of as chance, namely coincidence – nevertheless plays a role. Many organisms perish, not

Скачать книгу