Sven Lindqvist, a traveler and historian, paints a broad-brush history of European colonialism, especially in Africa. Drawing his title from Joseph Conrad's fable Heart of Darkness, he turns up 19th-century newspaper accounts of British massacres of wounded Sudanese rebels after the siege of Omdurman, of German concentration camps in what was once called Southwest Africa, of a Belgian captain who decorated his flower beds with the heads of recalcitrant plantation workers. These incidents were not unusual, Lindqvist writes. Neither were they thought especially brutal by their perpetrators, for, he argues, colonialism was guided by a doctrine that placed Europe at the top of the evolutionary ladder and regarded non-Europeans as a separate species bound for extinction--a doctrine that found its ultimate expression in the Holocaust. This is an occasionally gruesome and always provocative study.