There may be no single cause of bipolar disorder (aka manic depression). Instead, research indicates the causes of bipolar disorder are probably a combination of biochemical, genetic and environmental factors that may trigger and perpetuate the chemical imbalances in the brain.
Net worth: $829 million. Telecommunications mogul Strive Masiyiwa is widely regarded as the richest man in Zimbabwe and is one of the richest men in Africa with a net worth of more than US$800 million.
The Great Zimbabwe, a Unesco World Heritage site near Masvingo in southern Zimbabwe, is a ruined city founded in the 11th century. Believed to have been the capital of the Shona people, it gave the nation its name. Credit Joao Silva/The New York Times.