"It is as if man had suddenly been appointed managing director of the biggest business of all, the business of evolution." Appearing in a 1957 essay by the biologist Julian Huxley on "trans-humanism" (a term that Huxley coined), this is a declaration that could be made by any number of Darwinian ideologues today. Evolution has never been just a scientific theory. Ever since it was first properly formulated by Darwin, the theory has been used to advance a variety of political projects. It is not only "social Darwinist" supporters of laissez-faire capitalism who have claimed that their political ideals were grounded in evolutionary theory. So have Nazis, communists, anarchists and Fabian social engineers. Today, Darwinism is invoked as part of a campaign against religion by people who claim to be liberals. Behind the rival political programmes to which Darwinism has been yoked lies Huxley's belief that humankind is now in a position to direct its future evolution.
The principal achievement of Darwin's account of evolution is that it dispenses with the idea of purpose or design. Evolution is a directionless process, producing highly complex forms of life only to wipe them out. There is no progress in nature, but in ethics and politics the idea of evolution is invariably joined with the hope of improvement. Generations of progressive thinkers have invoked Darwinism to prop up their visions of a more advanced society. But the content of these visions has shifted over time, and one of the virtues of The Political Gene is to show how often Darwinism has been used to promote ideals of human progress that are illiberal, authoritarian or racist.
Drawing an implicit parallel with The Black Book of Communism, published in France in the late 1990s, which detailed communist atrocities ignored by bien-pensant opinion, Dennis Sewell writes that "the Black Book of Darwinism contains some real horrors". A large part of The Political Gene focuses on how leading Darwinists have campaigned for eugenics. Francis Galton (1822-1911), one of the founders of modern psychology, used Darwin's theory to promote his field as "an upbeat project offering an optimistic hope of Utopia", even writing an unpublished novel, Kantsaywhere, about a republic ruled by a Eugenic College, whose fellows set and administer "anthropometric tests" measuring the "fitness" of the population. Galton's repulsive utopia may seem remote from any 20th-century political reality but, as Sewell shows, eugenic ideas of the kind Galton propagated were taken seriously, not least in the United States, where 33 states passed sterilisation laws and at least 60,000 people were sterilised as "unfit".
In Germany, the chief propagandist for Darwinism was Ernst Haeckel (1834-1919), who, like Galton, promoted the idea of a racial hierarchy. Holding that "the lower races . . . are psychologically nearer to the mammals - apes and dogs - than civilised Europeans", Haeckel was pivotal in giving scientific respectability to the categorisation of race. The extent to which his ideas were used by the Nazis is disputed, but there can be little doubt that his enormously influential writings helped open the door to racist pseudo-science in Europe.
Certainly, versions of Darwin's theory were recruited in support of some thoroughly unpleasant causes and, when linked with racist theories, they created a climate in which genocide could be represented as a scientifically defensible policy. It is at this point that 21st-century defenders of Darwinism will be up in arms, indignantly protesting that these were abuses in no way entailed by the theory of natural selection.
They have a point. Darwin did write of "civilised man" replacing the "savage races", but he never advanced any theory of innate racial inequality. While eugenic movements have always been prone to racism, eugenic theories need not - as a matter of logic, at any rate - accept race as a scientific category. More generally, one cannot hold a theory responsible for the uses that are made of it, if only because judgements of value do not flow automatically from explanatory claims.
This last point is confirmed by the diversity of contending movements that have claimed a pedigree in Darwinian thinking. Nazi exponents of "scientific racism", communists who believed in a collectivist future for humanity, anarchists who followed Peter Kropotkin in thinking evolutionary theory vindicated the importance of mutual aid, advocates of laissez-faire such as Herbert Spencer (who invented the expression "survival of the fittest") and high priests of social engineering such as Lord Beveridge - a long-standing advocate of eugenics, as Sewell demonstrates - can't all be right. It might seem reasonable to conclude that they were all wrong, and say that no moral or political position can be derived from Darwinism.
Yet matters aren't quite that simple. Contemporary evangelists for Darwinism continue to claim that it supports a particular political programme - in this case, a militant version of secularism - and aim to convert humanity to what they see as a scientific world-view. The logic of their position has never been explained. A phenomenon that is nearly as universal as religion is likely to have some evolutionary role and, even if religions are illusions, the upshot of Darwinian science may be that the human animal cannot do without them. In that case, Darwinism would suggest evangelical atheism is a pointless, indeed absurd, activity.
What actually happened was that evolution was promoted as a faith. Galton hoped that eugenics would one day have the authority of the church. Haeckel set up his "Monist League" explicitly in order to found an "evolutionary religion". And, for Huxley, transhumanism was quite obviously a religion-substitute.
Sewell tells us that this is not mainly a book about religion. Rather, it addresses the intersection of evolutionary theory and politics. But his decision to limit himself in this way is unfortunate. He misses out the vast tracts of social science in which the idea of evolution has had a central role. Think of the innumerable tomes stacked on the shelves of university libraries (nearly all, fortunately, long unread) that contain "social evolution" in the title. The notion that societies "evolve" over time, with some becoming more "evolved" than others, has been floating around for generations. Yet it is little more than a misleading metaphor. There is nothing in society analogous to natural selection, or - despite silly talk of memes - anything comparable to genes. Like the more overtly political uses of Darwinism that Sewell examines, theories of social evolution are strategies for giving prevailing values the authority of science. Nearly always, theorists postulate a future filled with enhanced versions of themselves - the onward march of progress, as they like to think of it.
In fact, evolution has nothing to do with progress, however progress is understood. But the confusion of the two is probably incurable. It expresses a central illusion of modern times - the myth that scientific knowledge can enable the human species to seize control of its destiny. The lesson of Darwinism is that species have no collective purpose. It is not "humanity" that uses the results of scientific inquiry. Instead, some human beings use science to control others. Happily, no group is likely ever to control humankind as a whole. Huxley's vision will remain no more than an ugly dream. Yet the appeal of this fantasy is unlikely to wane, because it satisfies the need for faith while offering the alluring prospect of power.
The Political Gene: How Darwin's Ideas Changed Politics
Picador, 320pp, £16.99
John Gray is the New Statesman's lead book reviewer. His most recent book is "Gray's Anatomy: Selected Writings" (Allen Lane, £20)