Plant Domestication

Around 12,000 years ago, maize did not exist. Teosinte, a tall and broad-leaved grass, transformed into maize through the process of natural domestication. Teosinte had few kernels and each was very difficult to crack open. Farming communities in Mexico realized that if they only replanted the teosinte variations that had many, easy-to-open kernels, only this form of teosinte would grow. This process of selective gathering and dispersal of teosinte pods led to the creative of maize 6,000 years ago. The following picture demonstrates this evolution.

(quora.com)