 Demography is the study of population. That effectively means births, deaths, migration. So where are people having many children? Where are they having few? Where's the number of kids going up and where's it going down? What age do people live to? How big is therefore the population? I mean, if you think of it, it's a stock with flows. The flows are births in, deaths out. So when you have a population with lots and lots of babies being born, not many people dying, like in much of Africa now, it grows very rapidly.