The journey of Teosinte to Maize

​About 8-10000 years ago, probably in the Balsas River valley of Mexico, someone or perhaps several people, found a mutant teosinte plant in which the hard fruit casing did not extend fully around the enclosed single seeded grain, the kernel.  Someone realized that this made the kernel very edible and consequently propagated some of the seed.  It was recently discovered that a single mutation in the TGA1 gene in Teosinte, changed a single nucleotide in the DNA code of this gene.  This resulted in an amino acid change (asparagine instead of lysine) component of a protein critical to the development of the seed case in Teosinte and corn. Not only were the starch components of the seed more easily extracted by humans, but removal of the hard case allowed for greater growth of the kernels.  This was only one of several mutations that ultimately resulted in we know as maize but we are appreciative that people a very long time ago, recognized the advantage of this mutation. A description of the mutation is in http://phys.org/news/2015-07-tiny-genetic-tweak-corn-kernels.html.
 
Other mutations assisted humans as they moved from a plant with about 20 seeds per ‘ear’ encased in a hard covering, into a plant that were easily used for food.  It is notable that the initial mutation was to an annual plant version of Teosinte, thus allowing for selection of new genetics each year. A thousand years could equal 40-50 generations of humans but is 1000 generations of corn, allowing a lot of opportunity for genetic changes as humans made selections for adaptation to the environments and their food.
 
There is archeological data supporting that the early corn, although originating in a valley in south central Mexico, was moved to the highlands of Mexico.  From there it was spread eventually to all continents.