How did anceant people selectively breed corn if they didn't know about genes and inheritance?

obviously they did.

They were smarter than people today, and they were not burdened with the "knowledge" that you can't do that. By smarter I mean they THOUGHT about things more than most people do today, not that they knew about computers. They were also more in tune with nature and much more observant. They saw that plants that did not get pollinated did not make seeds. They saw that the healthiest man and woman made the strongest baby. They learned that when they crossed the best goats they got better goats. So they experimented, they tried hundreds, maybe thousands of crosses. Corn worked.