How does having more kids than you can afford generate wealth?
A single man with no kids making 30k a year has a better chance at advancing and generating wealth than the same single man making 30k a year with one child.
Having an Abortion doesn't mean you don't already have children.
The africans that are having all of those kids are likely living in agricultural environments where more kids equates to more hands working on the farm, meaning more prosperity. In cities, where everything is more expensive, yes, having more kids is a detriment because the cost per kid skyrockets.
Americans had big families going as far back as our parent's generation. Most families were large and yet that didn't stop the progress of the American economy. We scaled back AFTER our economy really developed, starting living in more urban environments and the cost of kid outpaced what was affordable.
The primary problem in Africa is NOT the rate of population growth. The primary problems are corrupt dictatorships, many of whom were installed by western powers, lack of infrastructure, tribal conflicts, droughts, famines and other similar issues.