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Before Darwin, the interpretation of life on Earth was trapped within a mode of thinking imposed by biblical traditions. Common observation

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shows that the living world is divided into different types of animals and plants, and that these

differences were maintained across generations. Lions mate and give birth to lion cubs, sheep mate and give birth to lambs. Cubs and lambs in due course grow into lions and sheep and mate in their turn. But lions do not mate with sheep, they eat them; at best, in the paradisiac vision of the Bible, they might lie down peacefully with each other. Even if such similar animal types as horses and donkeys can mate, the result is a sterile cross, in this case a mule. Similarly with plants: nasturtium seeds turn into nasturtiums, hazel nuts into hazel trees. Thus each type or species was believed to be qualitatively distinct and to breed true -- a Platonic natural kind, that is. According to biblical myth, life on Earth began during the seven days of Genesis, when God individually created the progenitor pair of each species. These proliferated until the days of Noah's flood, when breeding pairs of all the world's species boarded the Ark and were thus spared to begin the process of repopulating the Earth once the

floodwaters had subsided.

The eighteenth century in Europe was the period of the Enlightenment, of the great systematizers and classifiers. The French worked on their vast Encyclopédie. Away in Uppsala in Sweden, the botanist Carl von Linné (known as Linnaeus) began the task of classifying all living species. A species was defined as a distinct group of creatures resembling one another in form and capable of fertile mating. Clearly, some species more closely resemble one another than they do other species, so they can be grouped together as, say primates (which include chimpanzees and gorillas) or ungulates (which include sheep and cows). But both primates and ungulates share with many other species the property of giving birth to live young (mammals), and with still more species the property of having a backbone (vertebrates). And so on. Related organisms could be assembled into nested groups, species within genera within families within orders within classes within phyla within, finally, the great kingdoms of animals, plants and fungi (bacteria only got classified later). But all species, however closely

interrelated, were regarded as immutable. They had persisted from the beginning and would continue until the end of time. Furthermore, all could be arranged upon some absolute scale of perfection,

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a Great Chain of Being, beginning with the lowliest and ending with that acme of God's creation, Humankind (Man) himself.

EVOLUTION

Enlightenment stability was not to last, however. Change was in the air, with the quickening pace of the Industrial Revolution. Human intervention, it was clear, could transform the appearance of species, domesticating and producing new varieties of sheep, cattle and dogs, although within a species even the most bizarrely differing varieties -- great danes and dachshunds, for instance -- are capable of fertile mating, however awkward the mechanics may prove to be in practice. This was also the period of intense interest in geology, not least because of its relevance to the extractive industries of coal and iron. As geologists explored the surface of the Earth and studied the strange objects that miners brought forth from its depths, they began to discover fossils -- the petrified remains of mysterious organisms at the same time both like and unlike those currently alive on Earth. Their existence in defined rock strata enabled them to be assigned dates, stretching back many millions of years. Perhaps species were not stable at all. Some living forms which had existed in the past did so no longer. But could they have been ancestors of present forms, into which they had gradually been transformed? This might account for all the family similarities which Linnaean classification had systematized.

Evolution simply means change over time (in fact, it shares a common etymological origin with the term 'development'), and by the beginning of the nineteenth century the arguments that species had indeed evolved -- that is, changed over time -- and that species currently alive were related, both to fossil ancestors and to one another, were relatively commonplace, at least among the freethinking intelligentsia. Erasmus Darwin, Charles's grandfather, a wealthy country doctor, amateur poet and botanist, argued thus. And so, above all, did the Paris-based naturalist and philosopher Jean-Baptiste Lamarck. Lamarck went further, seeking to offer a mechanism by which evolutionary change might conceivably occur. He found it in

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terms of individual life experience. Each creature strives to survive, and to do so must endeavour to improve its capacities and skills. Thus, in his famous example, an early ancestor of the giraffe,

endowed with only a relatively short neck, could be imagined as stretching up to reach the leaves of the trees on which it fed and thus lengthening its neck, if only imperceptibly. This imperceptible

lengthening would then be transmitted to the giraffe's progeny, and over the generations giraffes with ever longer necks would appear. 2

Lamarck's mechanism has been the butt of cruel jokes by Darwin's advocates for more than a century now, despite periodic attempts by more flexibly minded biologists to revive or even test it. Where it collapses is in the repeated failure to find reproducible evidence that characters acquired during an organism's lifetime can thus be perpetuated, except in certain rather ambiguous and highly constrained testtube experiments. As the child of fairly orthodox Jewish parents, I was circumcised at birth, just as all other Jewish and Muslim males have been for generations. But the fact that for some four thousand years and two hundred generations my male ancestors had been circumcised did not (as far as I know!)

have any effect on the length of my foreskin. Such examples are commonly cited to disprove Lamarck, though since an eight-day-old Jewish boy doesn't exactly strive to have his foreskin removed it isn't exactly what Lamarck had in mind. His model does require some positive effort on the part of the animal. None the less, it is the failure of Lamarckism that lies behind Crick's formulation of his Central Dogma: 'once "information" has passed into the protein it cannot get out again'.