"An American Flying Fortress on its way to Britain from the southern states of America crossed the Atlantic from south America and on their way they picked up a monkey as a mascot, " he said.

BBC: Statue for Tojo, the monkey who dropped in for a drink

In consequence, says Ms Wilkerson, who uses the words coloured, Negro and black in line with the practice of the day, by 1980 half of America's blacks lived outside the southern states.

ECONOMIST: Black migration in America