In 1985 a group of anonymous female artists in New York began dressing up with gorilla masks on their heads and putting up fly-posters around the city's museums and galleries. We hear from two of the original Guerrilla Girls, who launched a campaign to demand greater representation for women and minorities in the art world. Also on the programme, the rarely heard voices of Africans who were forced to take sides in WW1; how Pluto lost its status as a planet, the invention of a revolutionary sign language, Makaton, in the 1970s, and changing 20th century theories of child rearing.

PHOTO: Some of the Guerrilla Girls in 1990 (Getty Images)