Before the green revolution there were a lot of very different wheat varieties around the world. In fact, if my memory is correct, during the selective breeding for high yields one of the breakthroughs came from a thick and sturdy stalked dwarf wheat from Japan. The stalk genes it had produced a stalk strong enough to carry the new large yields.
The point being, we used to have a large variety of geno and phenotype around the world, and now we don't.
population responds to available food. if there was a 50 year food boom, population also boomed. setting food levels back to prior values creates a lot of economic pressure to find cheap food. If 1/5 of the calories humans consume need to be obtained from some other source, the economics get weird.
