@astoundedgoat
Prince William doesn't study population rates himself. He can only be guided by the experts that do. I'm not saying you're not an expert, you may be and think differently. Here are the predictions made as printed in Quartz Aftica, Statista and The Economist. The Economist addresses why educating girls, in the short term, won't prevent the population boom.
Quartz Africa
(By 2100) total population in Africa will triple in the same period.
To be clear, a population boom in Africa has long been on the cards with earlier estimates showing that more than half of global population growth by 2050 will occur in Africa. However, the Lancet’s new findings cover a longer timeline and also corroborate earlier forecasts which show that Nigeria, already Africa’s most populous country, will drive the boom in Africa with an expected population of 790.7 million by 2100.
While several African countries will have lower fertility rates by 2100, the impending population growth will be due to its young population and the current high fertility rates across the region with only seven African countries—Cape Verde, Botswana, South Africa, Morocco, Algeria, Tunisia and Libya—having fertility rates lower than the global average of 2.37 births per woman.
Statista
According to the forecast, Africa's total population would reach nearly 2.5 billion by 2050. In 2020, the continent had around 1.34 billion inhabitants, with Nigeria, Ethiopia, and Egypt as the most populous countries.
The Economist
Most experts agree that, if it continues at its current growth rate, like Nigeria, Africa’s population will double by 2050. That would be 2.5bn people, meaning more than a quarter of the world’s people would be in Africa. Few question those figures because much of the growth is already baked into what demographers term “population momentum”—that is, Africa has so many women of childbearing age that even if most decided to have fewer babies today, the population would keep expanding.