Other families have no hope of restoration. Bones dug up in a cellar in Ekaterinburg in 1991 were suspected to be those of the last Tsar and his family, shot in 1918. Checks of their DNA against modern relatives proves that the skeletons are, indeed, the remains of the Romanovs. Intriguingly enough, the skeleton of one young girl imprisoned with the group was missing. A woman known as Anna Anderson (who died in Virginia in 1984) claimed for many years to be the absent child, Anastasia, the daughter of the Tsar. Her assertion was rejected by a German court, but was accepted by thousands of emigre Russians. A check of the genes contained in a sample of her tissue found after her death showed her not to he related to the Romanovs, but instead to be (as many had suspected) a Pole, Franziska Schanzkowska, who had been rescued from a suicide attempt in a Berlin canal and ever after believed herself to be of noble blood.

Anna Anderson's claim to the Russian Eagle was false; but everyone has been granted a genetic coat of arms to democratize the search for descent. Like that of the Romanovs, it records who the forebears were and from whence they came. When people move they take more than their escutcheons. The DNA goes too, so that maps of genes do more than just record ancestry. They recreate history. A Message from our Ancestors

History itself may suggest where to start. Alex Haley, in his book Roots, used documents on the slave trade to try to find his African ancestors. He found just one, Kunta Kinte, who had been taken as a slave from the Gambia in 1767; and later became suspicious of the tales told to him by a native story-teller upon which Roots was in part based. The genes of today's Black Americans might have solved his problem.

The African slave trade began in the days of the Roman Empire. By AD 800 Arab traders h;ul extended it to Europe, the Middle Hast and China. In (he fifteenth century the Spanish and Portuguese started what became;t mass migration, at first from the Guinea Coast, modern Mauritania. Mediaeval Venice had black gondoliers and by the sixteenth century one person in ten in Lisbon was of African origin. Soon, a bull of Pope Nicholas V instructed his followers to 'attack, subject, and reduce to perpetual slavery the Saracens, Pagans and other enemies of Christ, southward from Cape Bojador and including all the coast of Guinea'.

The main trade was to the New World. About fifteen million Africans were shipped across the Atlantic. They came from all over West Africa and were dispersed over much of North and South America. The United States imported less than a twentieth of the total, but by the 1950s the USA had a third of all New World people of African descent, suggesting that slaves were treated less brutally there than in the Caribbean or Brazil. Slaveowners had their own preferences. In South Carolina slaves from the Gambia were favoured over those from Biafra as the latter were thought to be hard to control. In Virginia the preference was in the opposite direction.

Many Africans have an abnormal form of the red pigment of the blood, haemoglobin. One of the amino acids has suffered a genetic accident, a mutation. This "sickle-cell' form protects against malaria. Its protective role has disappeared with the control of the disease in the United States, but many thousands of Black Americans still carry the gene as an unwelcome record of their past. Anyone, however light their skin, who has the sickle-cell variant must have had at least one African ancestor. The disease was first recognised in 1910, and was at once used as a statement of racial identity: anyone with the illness (whatever their colour) must, by definition, be a Negro. Indeed, its very presence was seen as proof of the degenerate nature of American Blacks. The related disorders in southern Europe also showed, in the words of one racial theorist, that such people were ^vno(white clear through' and that their immigration to the I ISA would 'produce a hybrid race of people as worthless.uul tuiile as the good-for-nothing mongrels of Central America/

The fact that many BI.il k Americans have a copy of the gene for sickle-cell haemoglobin s.iys little more than that they originated in West Africa, which we knew already. Molecular technology tells a tale of just who the 'mongrels' are. It uncovers a mass of variation around the haemoglobin genes and gives an insight into the ancestry of many Americans, black or not; including the great majority who do not carry a copy of sickle-ceil at all.

The ONA in this part of the genome varies from place to place within Africa. The sickle-cell mutation itself is associated with different sets of DNA letters in Sierra Leone, Nigeria and Zaire, probably because it arose several times. The DNA around the normal version of the gene also varies and this, too, can be used to track down where in Africa the ancestors of today's Americans came from.

That continent contains more diversity than anywhere else. Not only are its people more distinct one from the other, but different villages, tribes and nations have more individuality, because humans have been in Africa for longer than anywhere else. As a result, genes can track down the ancestry of Africans with some accuracy.

Black Americans from the north of the USA have a different set of variants from those in the south. The majority of northerners share a heritage with today's Nigerians white their southern cousins have more affinities with peoples further west. The difference in the slave markets two hundred years ago has left evidence today. Alex Haley, by comparing his genes with those from Africa, would have learned much more about his fort-fathers than he could hope to uncover I mm the records, lor any black American, a DNA test could be.1 first him as to where to search for his slave ancestors — and, for a mere $2.50, one is now on sale (although the limited information yet available on the genes of West Africa mean that any hope of finding his native village — or even tribe — is largely vain).

Many of Alex Haley's ancestors were probably not black at all. One particular variant in the Duffy blood group system is found only in West Africa. Europeans have a different version of this gene. Surveys of United States Blacks show that up to a quarter of their Duffy genes are of white origin, in many cases because of inter-racial matings during the days of slavery. Such liaisons were covert, but widespread. Even President Thomas Jefferson is said to have had several children by his slave mistress, Sally Hemings. The conjecture was proved by the discovery that one of her descendants carries DNA shared with that of the President's family (a proof so firm that it has been accepted, grudgingly, by the association of Jeffersonian descendants).

A closer look at a set of DNA clues specific to Africa or to people of European origin says more about the history of slavery. In Jamaica (where whites were a small minority), just one black gene in sixteen is of European origin. In most American cities the figure is around one in six, butin New Orleans is higher, at between a fifth and a quarter. Until 1803, Louisiana was under French, rather than Anglo-Saxon, control. Gallic racial tolerance lives on in today's genes. The differences in numbers of blacks and whites, and the small proportion of white families that have mated with blacks has transferred far fewer black genes into the American population that sees itself as white, with an overall proportion of about one gene in a hundred.