The philanthropist warns that stability in Africa makes a huge difference to the world, and that investing in the health and education of its young people is vital What worries Bill Gates most? The booming population of Africa looms over his foundation’s latest global survey. By the end of this century there will be 4 billion more people on earth – and 3 billion of these extra souls will be born in Africa. The challenge, he says, is that “Africa must almost quadruple its agricultural productivity to feed itself. That’s very daunting.”