More than half of Brazil's population is Black, but most have no idea of their precise origins. They only know the broad outlines of their history and the fact that their African ancestors were enslaved and shipped over by the millions. After the abolition of slavery in 1888, the finance minister of the time ordered the destruction of all documents relating to the slave trade. Today, many Brazilians are searching for their roots and some are even taking DNA tests. Our correspondents Fanny Lothaire, Louise Raulais and Tim Vickery report.