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Although history is not made entirely, or even mostly, by prominent men and women, two great exceptions to that rule were born exactly 200 years ago today, on 12 February 1809: Charles Darwin and Abraham Lincoln.

These men shared more than just a birthday, the loss of a mother in childhood and a date with immortality. They shared a position on one of the great issues of their age: the 'peculiar and powerful interest' of their fellow humans bound in slavery. When he circled the world in the 1830s, Darwin's delight at our planet's natural riches was repeatedly poisoned by the cruelties he saw meted out to slaves. “I thank God, I shall never again visit a slave-country,” he wrote at the end of the Voyage of the Beagle.

A new historical study, Darwin's Sacred Cause by Adrian Desmond and James Moore (see page 792), seeks to unite Darwin's revulsion at slavery with his scientific work. It was common at the time to believe that the different races of men had been created separate and unequal. But the abolitionist beliefs that Darwin derived from his family, friends and social setting strongly disposed him to the idea that all men — Englishman and Hottentot, freeman and slave — were brothers united in shared ancestry. The ability to see that unity-in-variety was, Desmond and Moore argue, one of the things that allowed him to perceive something similar in the natural world as a whole. As Darwin wrote in an 1838 notebook, “I cannot help thinking good analogy might be traced between relationship of all men now living & the classification of animals.” When Darwin sketched life's common descent as a family tree, it was because he believed in a family tree for humans — a belief in common kinship that was not a disinterested scientific finding, but rather an expression of moral and political persuasion. Darwin's thought always extended beyond the natural world. His ideas always had, and were meant to have, a social dimension.

Lessons from history

For all Darwin's noble ambitions, the century and a half since On the Origin of Species have shown how easily his image of a fiercely competitive world can be used to bolster pre-existing positions of power and privilege with buttresses of support that seem founded in an impartial consideration of the natural world. The history of arguments about humanity based on biology — both Darwin's biology and that of others who have come after — provides a sorry rehearsal of pretexts and apologias for everything from unthinking prejudice to forced sterilization and genocide (see page 786).

This history counsels caution as ever deeper and subtler forays into the science of human nature become possible. Deciphering the traces of natural selection in the human genome (see page 776), and dissecting the genetics of neurobiology and behaviour promise a new, more detailed and complex sense of how of how evolution has given human nature a definite biological form — while at the same time throwing new light on just how deeply biology can be influenced by society and culture. This is a rich field for research in both the natural and the social sciences, especially in the form of new collaborations between them (see page 780).

It is vital, however, that this new knowledge should be judged by far higher standards than the ideology passed off as biology that blighted so much of the twentieth century. Scientists have beliefs about what is right and wrong, just like everyone else. And try as they may to put them to one side — some try hard, some not so much — those beliefs will influence the way they do science, and the questions they ask and fail to ask. The scientific enterprise as a whole has to pay particular heed to the risk that preconceptions will creep in whenever what is being said about human nature has political or social implications.

This is particularly the case when science begins to look, as moral psychology is doing, at the mechanisms by which people make decisions about right or wrong. Here it becomes peculiarly hard — and at the same time especially important — to resist the 'naturalistic fallacy' of inferring what ought to be from what is. Science may be able to tell us why some values are more easily held than others. But it cannot tell us whether taking the easy path in terms of which values we espouse is the right thing to do.

In fact, it provides us with a worked example to the contrary. The scientific endeavour itself is founded on values which natural selection would have seemed unlikely to foist on a bunch of violent, gregarious upright apes. Science tries to place no trust in authority; to some extent, society has to. Science tries to define its membership on the basis of inclusion, rather than exclusion; work on altruism suggests, worryingly, that communities more normally need an outgroup to form against. Science insists on the value of truth even when it is inconvenient or harmful; most people's beliefs tend to reinforce their self-interest.

In this unnaturalness lies the great strength of science. It is from this it derives its power as a way of understanding the world. And this is also what allows it, at its best, to resist, not reinforce, mores and prejudices that pose as truths of nature. This demanding, artificial code is what gives engaged, passionate and all-too-fallible human beings the collective power to produce results that are dispassionate, objective and reliable. And if science stays true to that code, it can act as a stern restraint on anyone seeking to go from the study of how people evolved to conclusions about how they should be treated now — to go, that is, against the values that both Darwin and Lincoln espoused.

Science can never prove humans alike in dignity, or equally deserving under the law; that is a truth that cannot be discovered. Like the ideals of malice towards none and charity towards all, it is something that must be made real through communal will.


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