[malloryerik]

Late comment but if technology brought down the price of food then people could spend less on food, more on other good and services. Or the same on higher quality food. You don't need an increasing population for that. The improvement in agriculture could mean some farmers would have to find other work. So you can have economic growth with a stagnant or falling population. And you can rather easily have economic growth on a per-capita basis with no overall GDP growth, like is common in Japan today.

About the farmer needing to change jobs, in the interview that is the subject of this thread Ilya Sutskever speaks with wonder about humans' ability to generalize their intelligence across different domains with very little training. Cheaper food prices could mean people eat out or order-in more and then some ex-farmers might enter restaurant or food preparation businesses. People would still be getting wealthier, even without the tailwind of a growing population.