Corn along with rice and maize are the basic grains used all over the world. They evolved in different parts of the world in different climates and conditions. Wheat for example is said to have been originated in Middle East. Rice requires plenty of water for cultivation and thus grown in the areas where rains are heavy or other sources of water are easily available. Here we are talking about the evolution of corn.
Evolution of the parent wild varieties have taken place through man’s method of selective breeding over the centuries. The history of modern-day maize begins at the dawn of human agriculture, about 10,000 years ago. Ancient farmers in what is now Mexico took the first steps in domesticating maize when they simply chose which kernels (seeds) to plant.
These farmers noticed that not all plants were the same. Some plants grew larger than others, or maybe some kernels tasted better or were easier to grind. The farmers saved kernels from plants with desirable characteristics and planted them for the next season’s harvest. This process is known as selective breeding or artificial selection. Maize cobs became larger over time, with more rows of kernels, eventually taking on the form of modern maize.
Evolution is said to be gradual and slow. But in the case of corn, it evolution occurred in a burst of fairly small time. After a long search, the scientists became sure about the ancestor of maize. Its name is Teosinte. Plants are totally dissimilar in physical appearance but their DNA is very similar and two can be easily crossed to produce modified intermediate varieties. Samples bear an unmistakable resemblance to modern maize.
Following shows a collection of sizes and shapes of cobs beginning from the earliest.
The author is thankful to the following link for the two diagrams and ideas