Scientists tend to have a consensus regarding the domestication of corn around 7,000 to 10,000 years ago in an area that is now modern-day southwestern or south-central Mexico. Corn spread relatively quickly all across the Americas and got to the northeastern United States and the southern portion of Canada shortly before the colonizers from Europe arrived.
Origin of Corn
Wild species of corn are known as teosintes and are vital parts of corn evolution even though scientists are divided concerning the various taxa involved. The most prominent model of corn evolution holds that corn was derived from Zea mays parviglumis as a result of the selection of notable mutations even if some varieties, as much as one-fifth of the genetic material came from the Zea mays mexicana via a process known as introgression.
All except for the teosinte species from Nicaragua can grow in or close to the cornfield and this allowed for introgression between corn and teosinte. The first set of hybrids and the ones that came, later on, are seen in the fields even if the rate of genetic exchange is decreased.
Several Zea mays mexicana displayed the phenomenon of Vavilovian mimicry on the cultivated maize fields. The evolution here happened because of selective weeding by the farmers. Even today in some parts of Mexico, teosintes are seen by some farmers as nothing but a pesky weed and in some other places, it is seen as a relevant companion plant, thus encouraging the introgression with the corn plants.
Initial Dispersal of Corn in the Americas
The initial corn gene pool can be divided into three groups, the first of which is called the Andean group which includes not just the Andean corn but the variant that has the ears shaped like a hand grenade – a total of 35 plants. Then there is the US corn, South American, and Mexican corn variants. There are also some other genomes considered to be intermediate or even admixtures of the various groups.
Scientists believe that the corn variants of the Andes Mountain with the distinct ear shape originated from the corn variety from the lowlands of South America which itself originated from the lowlands of southern Mexico and Guatemala.
Corn as we have it today in the modern form is possible only because of human interference. There is copious proof from genetic and archaeological studies show that corn underwent breeding and cultivation by the early settlers of Mexico as far back as 10,000 years ago. The first generations of the Mesoamericans were able to develop corn from the grassy ancestor via the process of selective breeding. As hinted in the sections above, the evolution of modern-day corn commenced with the wild ancestor named teosinte.
The evolution of corn is so thorough that teosinte is nothing like the corn that we are all familiar with today. They are so different than the first scientists to study them in the field of botany did not even think that they were connected at all and this is apparent with even the physical characteristics. One ear of teosinte measures around three inches in length and has only around five to 12 kernels. If you are going to do a comparison with the maize today, you will notice the striking difference as the modern variant has more than 500 kernels.
The kernels of teosinte also have a very hard and tough shell. Across the generations, the Americans of the old chose and bred the plants with bigger ears and softer kernels. That explains why the corns today have the hard shell that has transformed into a flimsy tissue that sticks in between your teeth when you are enjoying a roasted or boiled cob.