Corn becomes corn

​As the early corn-teosinte crosses were moved away from Teosinte locations in the valleys of southcentral Mexico, the intermixing with Teosinte genetics must have lessened. After hundreds of generations and selections by people from central highlands of Mexico, north into current southwest USA and south to Northern South America.  Aided by natural open pollination, and mutations, different types of corn evolved.  There were dented, semi-dented and flinted kernels with colored the non-colored aleurone layers and yellow and white flinty or floury endosperm. There were sweet corn and popcorn types 5000 years ago.
 
Whereas Teosinte needed to survive with seed naturally distributed by dehiscence from its ‘cob’, people selected types that would retain the seed on the cob.  Corn became dependent upon people to grow the next season. It also became easily transported by people as it spread to Southwestern US about 3-4000 years ago. From there it spread as far north as Alberta Canada. There is evidence of corn in central USA by 2000 years ago and that it reached the Northeast USA about 1500 years ago.  Movement away from the equator required changes in the factors influencing the time to flowering.  Heat accumulation became a more significant trigger to stimulating the change in the meristems to produce flowering parts instead of more stem and leaf tissue.  Development of modern corn varieties are the result of those multiple selections done by many people across multiple environments several thousand years ago.