I don't see this minimization (after all, we currently do this unintentionally today and nobody sees this as lack of intelligence and I certainly hope I never implied that people in the past were in any way less capable than ourselves) but I do affirm that people were just as capable of understanding the causes and effects of plant reproduction as they are today.
I'm just freely speculating on how to find the most minimal path to explanation and it's easier to explain the differences in the rise of civilization in the middle east vs the new world with other factors rather than something cultural or genetic or otherwise abstractly geographically-bound factors. And besides, I like the idea that people in the past wouldn't have just sat around ruminating how to maximize crop yields but had more fruitful activities to attend to. I don't celebrate the egyptian engineer who figured out how to haul a multi-ton brick up a high slope, I mourn for him (or her)!
EDIT: softened wording a bit