There are 27.7 million people in Uganda. But by 2025 the population will almost double to 56 million, close to that of Britain, which has a similar land mass. In 44 years its population will have grown by nearly as much as China's. You look at these numbers and think 'that's impossible. Well, wake up, because this is the harsh reality. A typical Ugandan woman gives birth to seven children - an extraordinarily high fertility rate that has remained largely unchanged for more than 30 years. Half the population is under 15, and will soon move into childbearing age. Only one in five married women has access to contraception. And not just in Uganda. Across much of sub-Saharan Africa the population is expanding so quickly that the planet's demographic map is changing. By 2050 Chad, Mali, Guinea Bissau, Liberia, Niger, Burundi and Malawi - all among the poorest nations in the world - are projected to triple in size. Nigeria will have become the world's fourth-biggest country. The Democratic Republic of Congo and Ethiopia will have vaulted into the top 10 for the first time. Nearly one in four of the world's population will come from Africa - up from one in seven today.