Why so negative?
It seems that Europe's population is actually declining, so is japan's, and a lot of advanced countries.
If they keep feed themselves right now, they should be so even 100 years from now, given the same condition (unless we have some drastic global climatic change).
it is the poor countries, whose economies are based in subsistence agriculture, that are having a huge population increase.
So, the other question is, do you have to bring all these countries up to the level of western europe/japan/us in order to stop the population boom? if we have to, then there will certainly not be enough resources for everybody (especially if everybody has to live like american do)?
I have a good counter example for this. You don't have to be super developed in order to have a clear stabilization of the population.
Even my country's Albania (which has about 6kUSD gpd), population growth has halted (from 2.2 children per woman in 1990, to 1.7 last year).
So, you don't have to get super developed to have a decline of 'overfertility'. It seems that bringing economies out of rural ones, and into more mixed (agriculture/services/technology), will help the population not to increase so much.
It seems that this is a noble goal to achieve for the rest of the world, and this guy helped on it.
And making crops more durable, and farmers more productive, will make people move out of villages and go to cities, and redirect economies to towards services/manufacturing/technologies, where education is more advantage, and having more kids is very expenvie.