Answer:
Fertility rates are among the highest in the world, so populations are growing quickly.
Step-by-step explanation:
Sub-Saharan Africa is a region that as a whole has the highest fertility rates in the world by far. The countries in this region are a low level of development and the vast majority of the people are working in the primary sector, mostly in agriculture. The people still keep pride in having a lot of children, but they also need them as a labor force for farming and herding, and on top of it religion has a huge influence, and that further boosts the fertility rates.
Having such high fertility rates, but also gradually improving healthcare and living conditions, mainly due to the charities and help from other regions in the world, has led to the rapid rise of the population. In fact, this region is responsible for the global population growth at present, as all other regions have fertility rates in decline. It is projected that sub-Saharan Africa will have such a big population growth during this century that it may reach Asia's population.