There is good evidence that millet, in the form of the broomcorn variety millet, may have been the first crop ever domesticated. Millet is a highly nutrition grain being rich in protein, B complex vitamins and iron. Millet is particularly important in arid and semi-arid environments as the plant is highly drought resistance.
Previously, it was thought that agriculture started in the Tigris and Euphrates river valleys sometime between 12000 and 7000 years ago with the so-called founder crops of wheat and barley. Agriculture then spread from the Fertile Crescent into the Jordan and Nile valleys and then into Europe. This theory states that agriculture was later developed independently in the Chinese river valleys, the Indus valley, South America, Central America and North America and Papua New Guinea.
Recently, digs in North China indicate that by as early as 8000 years ago the millet seeds being consumed by domesticated animals were of the domesticated varieties to the exclusion of the wild varieties. From there, millet growing spread slowly westward until by 5000 BCE, millet was being grown in and around the Black Sea region of what is now Russia. Archeologist Dorian Fuller of University College London says: “Domestication of millet was apparently under way in northern China at a time when farmers in the south were just beginning to cultivate wild rice.”
Using this new data it seems that millet and rice, rather than wheat and barley, were the original founder crops. Then millet planting as well as the very idea of agriculture spread westward by diffusion. The advantages of millet as a staple food are the same as those for wheat and barley. That is to say like wheat and barley; millet can be soaked in water, boiled and eaten as gruel. Because millet is gluten free it cannot be used to make raised bread, but is used to make flatbreads. Further, millet can be soaked in water and left to naturally ferment to make a crude beer. many civilizations developed from this base of growing crops to bake bread and brew beer.
It is this flexibility in products that can be made from staple crops that allowed humans to use them and gain a food advantage from these crops over simple hunting and gathering. It is this action that allowed humans to settle down in one place, grow the population and develop civilization.
Childe, Gordon. Man Makes Himself , Oxford University Press, 1936
Balter, Michael. http://news.sciencemag.org/sciencenow/2009/03/25-01.html?rss=1