Did Charles Darwin believe in racial inequality?

Among the family heirlooms that Charles Darwin inherited, symbolically speaking, was a china cameo depicting a black slave in chains, asking "Am I not a man and a brother?" The image had been mass-produced as a campaigning device, some 20 years before Charles's birth, by his grandfather, the potter Josiah Wedgwood. An impassioned and active opposition to slavery was at the heart of the Darwin-Wedgwood family's values.

The cameo's question has long since been answered once and for all in the affirmative, but the questions about race that led on from it seemingly refuse to accept that they have been settled. Religion may have monopolised Darwinian controversy lately, but race remains a source of unease and suspicion. The fault-lines Adrian Desmond and James Moore have been treading in their new book Darwin's Sacred Cause: race, slavery and the quest for human origins (Allen Lane, £25) are still active.

When Charles Darwin entered the world 200 years ago, there was one clear and simple answer to the slave's question. All men were men and brothers, because all were descended from Adam. By the time Darwin had reached adulthood, however, opinions around him were growing more equivocal. During his vision-shaping voyage on the Beagle, he was able to consult an encyclopedia which arranged humankind into 15 separate species, each of a separate origin.

By the mid-19th-century, many influential voices denied that the enslaved African was a brother, and it was broadly taken for granted that as a man, he was of an inferior sort to his white master. Darwin stepped into the centre of the stage just when such ideas were helping to tear the northern and southern states of America apart.

To many scientists, that doubtless seems no more than coincidence. Darwin's devotion to observation and experiment, epitomised by the eight years he spent studying barnacles, lends itself to the interpretation that his concerns were solely with the facts of nature. In the introduction to his book Darwin's Island: the Galapagos in the garden of England (Little, Brown, £20), Steve Jones seems to suggest that we would do well to follow "the tradition of the great naturalist himself, who was dubious about the many infantile attempts to apply his ideas to society". That goes for the "empty arguments" about evolution and religion too. "Today's biology in its success emphasises how little relevance it has to the issues so often, and so tediously, discussed by non-biologists," he remarks.

The rest of us thus put in our place, Jones makes his point with a tour of topics that Darwin explored in his fleet of mature works, steering away from the flagships The Origin of Species and The Descent of Man. Jones cross-fertilises Darwin's pioneering studies of animals' expressions, orchids' contrivances and earthworms' exertions, among other subjects, with his own vivid and eclectic resumé of what science has discovered about these and much more since.

This is not the reflection on Darwin's relationship with his home in Kent and his native land that the title suggests – Darwin's biographer Janet Browne has already provided such a study in her volume The Power of Place – but it's certainly a showcase for the success of biology.

For those who feel that there is more to science than nature, however, Adrian Desmond and James Moore offer a bold new account of what drove Darwin on. His opposition to slavery in principle is well known, as are his appalled reactions to the evidence of its brutality he encountered on his Beagle voyage, such as the use of thumbscrews to punish slaves, or the man who cowered at his harmless gesture, reflexively anticipating a blow. What's new in Desmond and Moore's interpretation is the idea that this humanitarian concern motivated Darwin's science and guided it on its unique course. Evolutionary thinking enabled him to rescue the idea of human unity, taking it over from a religion that no longer provided it with adequate support, and put the idea of common descent on a rational foundation.

Desmond and Moore resume the bravura style they employed to dramatic effect in their 1991 biography of Darwin, spurring the historical horses into a gallop, striding across far-flung shores, echoing the thunder of distant battlefields, anatomising the machinations of power, and spicing the whole with artful touches for the reader to relish. Yes, Darwin surely was "the most gentlemanly gentleman anyone had ever met".

Their new Darwin differs somewhat in emphasis from the earlier one. After an encounter with "savages" in Tierra del Fuego, Darwin exclaimed in his diary "one can hardly make oneself believe that they are fellow creatures". In 1991, Desmond and Moore observed that he "almost begrudged them the status of 'fellow creature'". In their new light, they affirm he "believed that the Fuegians were 'essentially the same' as himself, 'fellow creatures' of one God."

It might have been more illuminating to admit his moment of doubt. Darwin was subject to conflicting impressions. He was not only sensitive to other people's suffering, he was sensitive to other people's opinions. In successive editions of The Origin of Species, he responded to criticisms by rowing back on his revolutionary idea, reducing the emphasis on natural selection and according more significance to other possible mechanisms of change.

As attitudes to race became harsher, sympathies for black people in the Americas more scant, and the fate of "savages" a matter of indifference, Darwin's own sympathies were blunted by the prevailing fatalism. Starkly displaying his own readiness to apply his ideas to society, he observed in The Descent of Man that "the civilised races of man will almost certainly exterminate, and replace, the savage races throughout the world".

Though he hoped that man would by then have reached a "more civilised state ... even than the Caucasian," he expressed no hope that extermination might be prevented by the kind of moral and political pressure that had by then achieved the prohibition of slavery in the US. It was simply inevitable. Nature would take its course.

In this passage, widely quoted by opponents of evolutionary theory, Darwin suggests that the break between "man and his nearest allies" will be widened through the extinction of the great apes, leaving a gap between the more civilised man "and some ape as low as a baboon, instead of as now between the negro or Australian and the gorilla". No doubt about it: he regards Africans and Australians as closer than Europeans to the apes. This, he implies, is a natural condition that will frustrate any cultural efforts to mitigate it.

Desmond and Moore emphasise how impressed he had been by the changes that his compatriots had induced in several Fuegians by forcing a crash course in European manners upon them: these "savages" readily showed a capacity to become civilised. But he was younger then, and so was the century: both were more idealistic and optimistic.

Desmond and Moore tell a story that is persuasive and emotionally compelling. It is frequently thrilling and intriguing too, offering a tumult of insights into the struggles around slavery, race and science. A particularly striking instance is the Confederate States' covert effort to manipulate British public opinion using agents in the Anthropological Society of London, who argued the case for slavery and flyposted Confederate flags on London streets.

They conclude with an explanation for the structure of The Descent of Man, which appears to be a book about human origins bundled with one about sexual selection, birds and butterflies fluttering through it. This was all part of the unity project, Desmond and Moore argue: Darwin saw sexual selection, in which basically trivial preferences shaped the appearances of populations over time, as a means by which races with a common origin could have acquired their visible differences.

Darwin thus emphasised human unity and dwelt upon superficial differences, while acquiescing in the contemporary assumption that some races were superior to others. At the time that Josiah Wedgwood's "A Man and a Brother" cameos were being fired in his kilns, three great principles were firing up on the other side of the Channel. Each was subsequently at stake in the interlinked questions of slavery and race. Liberty was the simplest. Darwin held to the conviction he grew up with, that human beings must not be bought, sold or owned. Fraternity was the principle that, in Desmond and Moore's reading, he worked to establish by building a theory of common descent. But equality was a different matter. Equality so often is.

Creationists of various stripes have seized the opportunity to include racism in their indictments of Darwin. From their point of view, it is one more wicked consequence of teaching that people are animals. Considering the comfort slave-owners in the American South drew from scripture, a selective biblical quotation comes to mind: the one about beholding the mote in thy brother's eye without perceiving the beam in thine own. On the other side, those who argue that some peoples are cleverer than others insist that theirs are scientific claims, to be judged by their content rather than their context, according to facts rather than values. Here modern idiom springs to mind: "Bring it on."

Desmond and Moore observe that their Darwin is "a man more sympathetic than creationists find acceptable, more morally committed than scientists would allow". Whether or not his sacred cause was what made him so special, their Darwin is a character that will speak eloquently to many people who have reached their middle years: somebody who strove to work the ideals of his youth into the fabric of a world that exalted some kinds of change, but had turned its face against others.

Marek Kohn's 'A Reason for Everything: natural selection and the English imagination' is published by Faber

Science and inequality: after Darwin

Francis Galton

Statistician and anthropologist

Charles Darwin's cousin, born in 1822, Galton made his name as a geographer of Africa. His later research in statistics and anthropology led him to apply his relative's breakthrough findings to human differences. As a strong proponent of the role of heredity in variations between individuals and groups, his championing of "nature" versus "nurture" was developed in the 1869 book 'Hereditary Genius' and then via the study of twins. In 1883, he coined the word "eugenics", and advocated strategies for improving human stock to give "the more suitable races or strains of blood" a better chance of success. His idea of "negative eugenics", designed to restrict the reproduction of less "fit" populations, would eventually feed into the policies of sterilisation followed by many from Nazi Germany to Social Democratic Sweden.

Arthur Jensen

Psychologist

The dispute over race, intelligence and heredity crackled into life again in 1969 when Jensen published, in the 'Harvard Educational Review', a paper entitled "How much can we boost IQ and scholastic achievement?" He concluded that heritable differences in intelligence between white Americans and African Americans meant that schemes to improve black children's performance would fail. His claims provoked lasting controversy both scholarly (in rebuttals such as Stephen Jay Gould's 'The Mismeasure of Man') and practical (student protests outside his office in Berkeley) as critics accused him of reviving 19th-century "scientific" racism. Jensen has continued to promote the genetic components of intelligence variations but, in 1996, his synthesis of research and arguments, 'The g Factor', was refused by publishers. It finally appeared in 1998.