I didn't claim the relationship was linear. People in poorer countries still have relatively abundant food by historical standards and aren't at risk of starvat

I didn't claim the relationship was linear. People in poorer countries still have relatively abundant food by historical standards and aren't at risk of starvation. However, when food availability drops below a certain threshold, reproduction rates tend to decrease - this is basic ecology. Historically, the most populated regions were also resource-rich, like the fertile river valleys. But we're now living in an era of abundance where even the poorer regions have access to plenty of food.