into a baby chick rather than a baby mouse or a baby tree? These were the great, unanswered questions of nineteenth-century biology. How is biological information encoded and how is it inherited?
One solution was reversion to the Platonic concept of ideal forms. In the realm of the perfect circle and the perfect sphere, there may also be the perfect form of a mouse, man or tree. This theory would, however, only work if species were themselves unchanging, reflecting the permanence of the proposed abstract realm beyond physical reality. In the eighteenth and early nineteenth centuries this did not present an obstacle since most naturalists believed in the continuity of species. The Swedish father of taxonomy, Carl Linnaeus (1707–1778) was first to systematically classify species of plants and animals and, like his contemporaries, he considered all species to be permanent, created by God; insisting, ‘There is no such thing as a new species.’
EVOLUTION
French aristocrat and naturalist, George Louis Leclerc, Comte de Buffon was among the first to question the immutability of species. Buffon noticed the presence of apparently vestigial parts in some animals, such as the bones of useless lateral toes in the pig. This led him to propose that species did change by degeneration of disused parts. His assertion that mammals degenerated in size in the New World provoked Thomas Jefferson to have the skeleton of a seven-foot moose sent to Paris, to prove ‘the immensity of many things in America’.
Jean Baptiste de Monet Lamarck (1744–1829) made a far more radical case – for transmutation of species. Lamarck came to science by a circuitous route. He was sent to a Jesuit school by his parents to train to be a priest but at sixteen his father died, leaving a small inheritance, just enough to buy a horse. Lamarck immediately left the priesthood and rode off on his new purchase to join the army fighting in Germany. After a brief (but reputedly glorious) military career, Lamarck moved to Paris to work as a bank clerk and in his spare time studied medicine, music and botany. His botanical publications impressed the influential Buffon who helped him to obtain a position as assistant in the botany department of the Jardin du Roi – the king’s botanical gardens. The French Revolution, bringing about the demise of his patron, was more favourable to Lamarck himself and he was elevated to the Chair of Zoology (but not botany) by the National Convention. One did not lightly refuse the dictates of a French revolutionary council so Lamarck turned his attention from plants to invertebrates.
Lamarck made many contributions to biology – not least its name. His career in both botany and zoology convinced him that all living things should be studied as a whole and so he introduced the term ‘Biology” (from bios, Greek for ‘life’) to encompass these studies. He was an accomplished taxonomist who was the first to separate spiders and crustaceans from insects. But his most famous contribution is his theory of evolution. Impressed by the similarity between many species of insects and other arthropods, Lamarck noted how it would take only minor modifications of form to change one species into another. He proposed that evolution had done exactly that and that modern species of plants and animals were descendants of earlier extinct species. The source of evolutionary change is what separates Lamarck from most latter-day evolutionists. Lamarck believed that characteristics acquired during an animal’s lifetime could be inherited by its offspring: the inheritance of acquired characteristics. His most famous example is the giraffe, which through many generations stretching for the leaves in topmost branches is proposed to have passed the acquired characteristic of a longer (stretched) neck to latter generations. Lamarck’s ideas were ridiculed at the time and have received a bad press ever since. Yet, they at least freed biology from the concept of the immutability of the species, setting the stage for the most famous theory of evolution.
In 1859, Charles Darwin published The Origin of Species and changed biology forever. A public thirsty for science eagerly awaited the book. All one thousand, two hundred and fifty copies of the first edition were sold on the first day of publication. The controversy and debate that ensued continues to reverberate today. What Darwin did in The Origin of Species and his later works, was to place man firmly in the material world, an animal like any other. To those who refused to countenance a place for themselves amongst our hairy cousins, it was (and, in some quarters, still is today) considered heresy.
Darwin did not of course invent the theory of evolution, but it was in his family. Darwin’s grandfather, Erasmus Darwin (1731–1802) was an eminent physician and keen amateur naturalist who proposed all organisms had descended from a ‘primal filament’. Yet Charles Darwin did not look likely, initially, to follow in his grandfather’s illustrious footsteps. His father, Robert Darwin, often harangued the young man, declaring, ‘You care for nothing but dogs and rat catching, and you will be a disgrace to yourself and your family’ This assessment looked increasingly probable as Charles dropped out of first, Medicine at Edinburgh and then Divinity at Cambridge. When, in 1831, the opportunity arose to serve as unpaid naturalist aboard the HMS Beagle, his father was at first opposed to the idea. It was only after the intervention of Darwin’s uncle, Josiah Wedgwood, that Robert Darwin was persuaded to allow his son to board ship.
Perhaps the elder Darwin did have a point about his rat-catching son because although Charles Darwin published The Voyage of the Beagle and several geological works in the years after his return from his voyage, he sat on his theory of evolution for twenty years. But in 1858 a letter arrived from Alfred Russell Wallace with an essay entitled, ‘On the tendency of varieties to depart indefinitely from the original type’. Horrified to find that Wallace had independently come to the same conclusions, Darwin’s first reaction was to abandon his lifework, but after much soul-searching and advice, he was persuaded to make a joint presentation with Wallace at the Linnaean Society. Darwin then set about organizing the mass of material he had collected over the years and published an abstract of his work, The Origin of Species by Means of Natural Selection or the Preservation of Favoured Races in the Struggle for Life.
What was original to the theory of Darwin and Wallace was that they proposed a mechanism to drive evolution – natural selection. The idea owes much to Malthus’ Essay on Population which argued that mankind will always produce more offspring than the available resources can support. The inevitable consequences, according to Malthus, are war, famine, poverty and disease, as increasing populations fight for limited resources. To Darwin, the same pressures amongst living organisms lead to natural selection or survival of the fittest. Only the fittest individuals will capture the resources needed to generate offspring.
The survival of the fittest is not enough in itself to bring about evolution because there is as yet no mechanism to generate change. The vital extra ingredient for natural selection is therefore inherited chance variation within a species. Darwin observed how all individuals within a species were very slightly different. Breeders of domesticated animals, such as dogs, have exploited these small differences to select animals with the desired traits, such as the shape of a face or the length of a tail. After centuries of breeding, quite distinct breeds, such as the poodle and the Great Dane, have been generated from the same ancestral wild dog. In the same way, nature could act as the selective force. These naturally occurring, randomly varying individuals within a species would compete for resources. With progeny always outstripping resources, only the fittest variants would survive to reproduce. Natural selection would tend to breed from those fittest individuals who possessed the most desirable traits. Over millennia, natural selection would bring about gradual change in plant and animal characteristics towards increasing fitness – descent with modification – evolution.
Publication of The Origin of Species aroused a great deal of criticism. But although the ensuing theological debate generated the greatest controversy (and still does), a very real scientific problem led Darwin to at least a partial abandonment of his original hypothesis. The difficulty arose with the commonly held belief at the time that sexual reproduction always led to the blending of characteristics. This blending would tend to wipe out variation – so that if poodles and Great Danes were allowed to mate freely, then their offspring would tend towards nondescript mongrels. The physicist H. C. Fleming Jenkin and many others held that no amount of selection for either the characteristics of poodles or Great Dane could result in their offspring being anything other than a blend of the two.
Without