Passage Summary: Ancient people switched to growing corn because it was more efficient, but it made them sick. Even though they knew it was making them sick and they could have switched back to healthier crops, they stuck with the corn.

Reasoning: Corn is more productive and grows faster than previous grains, but it is less nutritious and caused health problems; despite this, and the ability to switch back, people continued using corn as their staple.

Analysis: The paradox here is a conflict between health and efficiency: why choose a crop that makes you sick when a healthier alternative is available? We need a reason why the benefits of corn (speed and quantity) outweighed the significant health costs. It is possible that the population grew so large that the 'healthier' grains simply couldn't produce enough total calories to prevent starvation. Look for an answer that explains why returning to the old grains was not a viable survival strategy despite the health benefits.