by Janet Browne
Indeed, the science of genetics at the start was somewhat anti-Darwinian. For more than twenty years its practitioners proposed that mutations were the source of new and favourable kinds of organisms – happy accidents that would introduce an entirely different kind of being into the natural world. These early geneticists had no need for natural selection. It took a lot of dedicated work in the 1930s and 1940s to see how Mendelism and Darwinism might be brought together.
Meanwhile, close attention was paid to identifying the inheritable material and how it was transferred from generation to generation. At that time, it was not at all obvious how chromosomes might be involved. In 1893 August Weismann proposed that there must be an invisible substance that carried all the hereditary information from parent to child. He called this ‘germ plasm’ and claimed it could not be affected by the environment. This germ plasm played a useful interpretative role until expanded by Wilhelm Johannsen’s definition of the ‘gene’ in 1911. Even Johannsen was unsure if the gene really existed until Thomas Hunt Morgan, the outstanding geneticist of Columbia University, New York, demonstrated that genes were, so to speak, real entities strung along the chromosomes like pearls on a necklace and that they definitely contained the heritable material. Morgan’s famous experiments depended on one particular experimental organism, the fruit fly Drosophila melanogaster, which happened to have large and easily visible chromosomes. By breaking or otherwise manipulating the chromosomes, Morgan’s laboratory team produced a succession of mutant flies, for instance with red eyes or fused wing covers. The work proceeded with such sophistication that the team could locate which part of the chromosome was specific to each mutation. The results were summarized in The Mechanism of Mendelian Heredity (1915), now regarded as a milestone in modern genetics, and for which Morgan received the Nobel Prize. His book was completely non-Darwinian. With a fine new theory of chromosomal mutations and the gene to answer every question, Morgan discarded Darwin’s ideas of variation, adaptation and selection.
The influence of the Origin of Species was subsiding elsewhere too. Other geneticists favoured environmentalist ideas of inheritance. Soviet communist governments were generally hostile to the capitalist implications of Darwinian theory in the twentieth century and endorsed a revised form of environmentalism brought into state policy by Trofim Lysenko in the course of the 1930s. Lysenko’s achievement had been to demonstrate the adaptation of wheat to prevailing climate conditions (‘vernalization’, in which the seeds were exposed to cold so that they would germinate earlier the following year). Lysenko claimed this property could be inherited and thus new breeds of wheat could be produced suited to the short growing season in Russia. Stalin adopted Lysenko’s findings, forbade alternative genetic research and instigated a purge of leading geneticists, notably Sergei Chetverikov and Nikolai Vavilov. Some fled to the West, such as N. W. Timoffeef- Ressovsky and Theodore Dobzhansky, and there contributed extensively to the rise of new genetic ways of thought. Others simply disappeared. Under this regime, reports of amazing (and impossible) agricultural successes were issued until the middle years of Khrushchev’s power, when Lysenko was denounced by the physicist Andrei Sakharov. It was the mid-1960s before Russian science gradually opened up to Darwinian ideas of evolution and the new genetics.
By the 1930s, in fact, it was difficult to see exactly where Darwin’s theory might still be relevant. Molecular biology was beginning; chemistry and physics were increasingly used to explore the inner structure of living matter; and laboratory techniques were making substantial advances in understanding the workings of the cell and mapping the genetic basis of heredity. Field naturalists felt themselves to be left behind in the academic contests of big biology. From today’s perspective it is almost unimaginable to envisage a world of biological research without the concepts of adaptation and natural selection, the intellectual tools that underpin so much of modern biomedicine, the environmental sciences, theories of human behaviour and psychology. So what might have stimulated a mass revival of Darwinism in the middle years of the century?
Historians agree that three diverging lines of research were forcibly brought together by a group of inspired young naturalists in the 1940s, a group including the writer and biologist Julian Huxley (Thomas Henry Huxley’s grandson), Ernst Mayr, an émigré field naturalist and philosopher-biologist from Germany, Sewell Wright, the American geneticist, George Gaylord Simpson, a vertebrate palaeontologist and
G. Ledyard Stebbins, an up-and-coming botanist and geneticist. The story of twentieth-century Darwinism lies with these figures who struggled to give it new meaning and integrate it with cutting-edge experimental disciplines. Putting the situation somewhat starkly, the field and observational naturalists who continued to feel themselves directly connected to Darwin’s own work had to reinvent themselves. Although they scarcely intended this to coincide with any other event, the ‘modern synthesis’ was in place just in time for lavish centenary celebrations of the publication of the Origin of Species in Chicago in 1959.
An important first step was the reconciliation of Darwin’s original proposals with early twentieth-century genetics. In effect, it was necessary to turn the external process of animal and plant evolution into changes in the frequencies of genes. Repeated small mutations in the chromosomes were consequently reinterpreted as building up the fund of variability needed for the raw material of selection. Every trait, it was now realized, exhibited a continuous range of variation, so that in a large population there would be plenty of differences circulating through the gene pool on which selection could work. One of the leading figures in this movement was the Cambridge statistician Ronald Aylmer Fisher, who created a mathematical model to show how the frequency of a favourable gene could increase in a population. Fisher devoted a significant portion of his resulting textbook to discussing the human implications: inspired by Pearson he was an ardent eugenicist as well as a liberal Christian who claimed to see God’s hand in biological progress. Another significant figure was J. B. S. Haldane, a larger-than-life individual who contributed notably to British public education in the inter- war period. Like others at the time, Haldane looked enthusiastically to Marxism. He campaigned against Fisher and eugenics. Haldane ultimately resigned his professorship at University College London in protest at Second World War militarism and went to teach in India.
The man who turned it all into a theory of population genetics was Sewell Wright at the University of Chicago. By 1920 Wright had developed a powerful mathematical procedure to explore the flow of genes in small populations of laboratory guinea pigs and hooded rats. He investigated natural populations in the 1930s and proposed that similarly small groups in the wild must be subject to what he called ‘genetic drift’. Wright’s metaphors of an adaptive landscape with mountain peaks and valleys proved an effective way of thinking about the extension or contraction of small knots of particular variations inside a larger population, each little group ready to rise or fall in numbers according to changing conditions. Wright’s work was made more widely available through successive editions of Theodore Dobzhansky’s landmark textbook, Genetics and the Origin of Species (1937).
Inspired by the fresh ideas in population biology, Ernst Mayr settled down at Harvard University to integrate his ornithological field studies with genetics. Of all the biological thinkers of the twentieth century, Mayr was perhaps unique in his grasp of both practical detail and philosophical vision. Like Darwin, he concluded that a new species might develop if a variant group of organisms was geographically isolated in some way from its parent population. Dobzhansky added to Mayr’s proposals by suggesting that there were probably other isolating mechanisms as well, such as behavioural characteristics or different breeding times, all of which would prevent two or more populations from merging. At the same time, G. G. Simpson reinterpreted the fossil record, smoothing out its stops and starts to accommodate the idea of continuous variation. He argued that transitional forms would be rare and therefore infrequently pres
erved, giving to the fossil record a false appearance of sudden big changes. Then Stebbins showed how a plant’s occasional doubling and trebling of the chromosomes could explain the sudden origin of dramatically different species in the plant world. All three managed to unite the apparent discontinuities of the living world with a genetically-aware reinterpretation of Darwin’s small and gradual steps. Julian Huxley brought them all together in a popular book published in 1942 called Evolution: The Modern Synthesis.
The only thing this group did not have was proof. Ever resourceful, and in much the same way as Morgan had found a Nobel prize in fruit flies, the newly reconstituted Darwinians turned with delight to the Galápagos finches and then the peppered moth, Biston betularia. The Galápagos finches subsequently became the best-known example of evolution in the world – not through renewed attention to Darwin’s writings, it must be said, but through the work of David Lack, a schoolteacher and amateur ornithologist.
Lack had come to Julian Huxley’s attention in 1938 and visited the Galápagos Islands soon afterwards to observe finch behaviour for an entire breeding season. After ten years’ further work in museums, he concluded that the beaks held the key to their evolution. Each species had become adapted to a particular foodstuff, thereby allowing diversification into many different niches. His book, Darwin’s Finches (1947), described the birds as an example of evolution in action. Featuring in countless biology textbooks, nature documentaries and popular evolutionary accounts, ‘Darwin’s finches’ rapidly became synonymous with the new Darwinism. The work carried out by Peter and Rosemary Grant from the 1970s in the Galápagos Research Station still provides the most influential field study of evolution ever conducted.
The peppered moth was equally successful. It became an iconic example of natural selection just in time for the 1959 centenary celebrations of the Origin of Species, although the case afterwards became surrounded by unsubstantiated accusations of fraud. The study was made in Britain by Bernard Kettlewell under the guidance of the pioneer Oxford University population biologist Henry Ford. The moth itself could hardly have seemed a better demonstration organism. In nature it exists in two forms, one a speckled black and white, the other a black mutation, called melanic. On ordinary oak trees, the first form is almost invisible. This advantage is reversed in polluted industrial areas where the black form is better camouflaged on darkened tree trunks. Kettlewell released quantities of both sorts of moth in two wooded sites, one near Manchester, where the trees were blackened by soot, the other in clean countryside in Dorset. He demonstrated that birds ate the most visible form, thereby operating a Darwinian selective pressure that allowed one kind of moth to survive and increase in number at the expense of the other. It categorically showed that selection could alter the frequency of particular genes (in this case the melanic gene) in a population. One summer, the famous animal behaviourist Niko Tinbergen spent a few days with Kettlewell filming wild birds picking the moths from a tree trunk. Now a natural history film classic, the old black and white film was shown on early television screens, a perfect way to display black and white moths against their black and white backgrounds. In recent years, government-controlled reductions in pollution have reduced the black form in Britain to the point that biologists now find it difficult to repeat Kettlewell’s observations.
A huge step in the unification of the biological sciences had been achieved. The modern synthesis transformed the old notions of selection and adaptive change and breathed fresh life into Darwin’s ideas. Biologists also took a new interest in Darwinian themes that emphasized observation and practical field studies. Many biologists at this interesting time looked back directly to Darwin himself. The centenary of publication of the Origin of Species, which was coincidentally also the 150th anniversary of Darwin’s birth, was an occasion for much celebration and revivalism amidst the rhetoric of future scientific advance. Some biologists wrote biographies of Darwin, others edited for publication his Beagle journals and notebooks, and others again made moves to preserve his house as a memorial and museum in which the significance of modern evolutionary science could be appreciated and explained. In their eyes, evolutionary biology was at last a recognizable scientific discipline. Darwin was elevated into its founding father.
The new generation of Darwinians also addressed the question of human ethics. Most of them were convinced that science confirmed the absence of any underlying plan or divine purpose built into the universe. G. G. Simpson, one of the architects of the modern synthesis, pointed out that it was impossible to regard the human species as the predetermined goal of random shifts in gene frequencies. Amusingly, he said that mankind was the result of a process that never had him in mind. The modern synthesis, in fact, was much less readily compatible with spiritual belief than any previous, more flexible, theistic evolutionary theory. From the 1950s, there was an increasing tendency for practising scientists to be disbelievers, at the very least when inside their labs. The essence of modern science, it was commonly said, was to seek answers in the world of evidence and proof, not to call on the divine or other supernatural factors.
A few found spiritual consolation in continued ideas of social progress. Scientific naturalism could take on the mantle of a religion, as once preached by Thomas Henry Huxley in his ‘lay sermons’ or articulated by philosophers William James and Charles S. Pierce. The evolutionary mysticism of Pierre Teilhard de Chardin’s Phenomenon of Man (1959) was also popular among those seeking spiritual guidance in evolutionary processes. The world of living beings, he suggested, was enclosed by a sphere of mental unity, called ‘Noosphere’. This predated the idea of cyberspace by some twenty years, and Teilhard de Chardin is primarily remembered now for influencing the engineers of silicon valley. Julian Huxley was generally sympathetic to these views and promoted a philosophy of humanism, rejecting the idea of a transcendental creator, but drawing on older nineteenth- century idealism to stress the human race’s responsibility to foster moral progress. As it happened, most biologists were willing to believe that humans were still special. Human intelligence, adaptability and social characteristics were still seen as indications of a higher level of development than in animals. Humanists felt that the human race was capable of moving onwards from biology to make a better world based on pacifist, altruistic social policies.
After the brutality of the Second World War, however, there seemed little point in glossing over the harsher side of animal behaviour. The founder of modern ethology, Konrad Lorenz, demonstrated the innate aggressive behaviour of animals and warned that humans, too, were endowed with similarly destructive basic instincts. The message was reiterated by Robert Ardrey in his work on the ‘territorial imperative’ and by Desmond Morris in a widely distributed popular text, The Naked Ape (1967). Soon the terminology of primate studies was spreading from science into common public usage. Advertising moguls enjoyed a particularly inventive time with their slogans about ‘alpha-males’. To be human, it seemed, was to be brutish.
Such an image of human nature as fundamentally selfish and aggressive did not go unchallenged during the peace demonstrations and love-ins of the 1960s. The grand old man of palaeo-anthropology, Louis Leakey, encouraged three female scientists to pursue actual observations of apes in the wild, the first time that this had ever been achieved to modern scientific standards. He placed Jane Goodall in Gombe Stream Reserve, near Lake Tanganyika in East Africa, to observe chimpanzees, and Biruté Galdikas in Sumatra for the orang-utans. Last, he put Dian Fossey to work in a gorilla reserve in Rwanda from 1967. These studies of apes in their natural habitat showed them generally to be family-oriented, loyal to their troop, and not aggressive unless frightened. As a result, there was renewed willingness to take seriously a closer mental and emotional relationship between apes and mankind. With wide connections to the public through magazines like National Geographic, these alert observational scientists were also among the first to stimulate political awareness of conservation issues.
Tension b
etween such notions has never subsided. Discussion of the thin boundary lines between animals and mankind, between science and human values, has most recently taken its cue from Edward O. Wilson’s Sociobiology: The New Synthesis (1975) in which animal and human behav- iour patterns are located in the genetic framework of each species. Wilson argued that all organisms are genetically programmed to guarantee the most reproductive benefit to themselves: males tend naturally to spread their ample sperm around as far as possible and females to conserve their valuable eggs. Males do not stick around to look after the baby, females search for the best, most committed father. All behaviour patterns could be linked more or less back to the genes’ drive to survive. In claiming this, Wilson did not deliberately intend to suggest that human lives are completely biological, although he did say that ‘the gene holds culture on a leash’. Nor did he propose that humans are little more than a bundle of genes. He agreed that societies are mostly constrained by political institutions, economic limitations and social convention.
Yet to critics, this deterministic approach, rooted in an unyielding science of genes, is difficult to distinguish from dangerously ideological uses of genetics. Sociobiology could easily be used to support claims for inbuilt differences in intellectual ability, ethnicity or gender roles. Religious thinkers resent the notion that moral values apparently derive from biological utility: that a mother cares for her child in order to ensure that her genes are successfully passed to the next generation. Left-wingers fear that such ideas might be taken up by the political right to justify conventions like the nuclear family or to avoid civic improvements and medical care because it seems easier (and cheaper) to believe in unalterable, hereditary, biological traits. People from the humanities decry a continuing reduction of human attributes to mere biology. This cultural and scientific argument continues unabated through the twenty-first century.