How humans made corn.

Corn or Maize is a staple food in many parts of the world, with total production surpassing that of wheat or rice. But it wasn’t always the high yield crop it is today. Ten thousand years ago a grass called Teosinte was domesticated somewhere in modern Mexico, the crop looked nothing like today's corn on the cob, the plant is highly branched, the kernels are small, few in number, not fused, and enclosed in a hard fruit case. But still, early farmers breed this grass into corn, so how did they do it?