Maize kernels are nicely rounded and heavy, but do not spontaneously scatter.  Human intervention is therefore essential for it to survive.  Maize is clearly a “human crop”.  Breeders use a technique known as “hybridisation” to obtain top performance varieties with excellent yields, even under the most difficult conditions for climate, insects or disease.  Over the centuries, the plant has become bigger and stronger.  Take, for example, the size of the corncob which, 7000 years ago, was on average only 2.5 cm (less than 1”) long, whereas today it is 30cm (12”) long!

It all began some 6000 to 9000 years ago, in a valley in southern Mexico where the locals had grown a forage plant known as teosinte grass.
 
Initial cross-breeding changed the plant to produce just one single stalk.  Then, 5 500 years ago, further cross-breeding produced much larger kernels with softer skin.  Without any intervention, kernels are eaten by animals and go through their digestive tract, but are not scattered on the ground;  so the plant needed farmers for propagation.  Finally, by 4 400 years ago, the kernels on the cob had moved closer together and the starch had become more digestible.  Without this genetic evolution, maize would have been, quite simply, inedible!
Humans thus played an active role in the long maize production chain and in the steady improvement of the plant.  The maize “sector” requires a wide range of skills and expertise, and many good spirits have hovered over the cradle of maize, from geneticists learning more about the genes and their properties, to the breeders and seed growers and ultimately the maize farmers who sow the plants, feed them, protect them, tend them and finally harvest them.

More than 200 types of maize are spread across the surface of the Earth, following amazingly diverse plant cycles, ranging from 60 to 70 days for the very early maturing type (Gaspée) and up to 10 or 11 months for late-maturing types grown in tropical regions.
There are also great differences in the height of the stalks:  from 30 to 40cm for “Gaspée” type plants, up to more than 10 metres in tropical regions and Mexico.  Depending on the varieties, one single seed sown can produce from 1 to 14 stalks, and each stalk can produce from just a few to around fifty leaves.  The kernels themselves display substantial differences, in volume, colour and the type of albumen (flinty, sweet or floury).
Maize grows at many different altitudes, adapting to climates ranging from semi-arid in Central America and Eastern Europe to very wet in South-East Asia.

In the early 20^th century, researchers in the United States developed the idea of cross-breeding varieties (lines) to produce new varieties with improved performance.  This was the beginning of hybridisation.  By the 1930s, hybrids were widely adopted for general use on the American continent.
In France, in regions where maize had been grown for a long time, farmers were initially reluctant to use these new hybrids, seeing them as a threat to their local maize.  Over the generations, they had gradually developed local varieties, suited to the climate, soil and local uses.  Abandoning them was interpreted as a loss of biological, farming and cultural heritage.
In France it took ten years, from 1950 to 1960, for hybrids to be adopted.
 
This widespread use of hybrids was the first maize revolution.  In the end, the new varieties were quick to prove their advantages over the “local” types.  But the American hybrids were not entirely suited to the climate and agronomic conditions of the old continent.  By 1957, the French agronomic research institute [INRA -Institut National de la Recherche Agronomique] had developed varieties called "early maturing hybrids", which meant maize could be grown further north in France and Europe.
 
In the 21^st century, maize will have to meet many different expectations and satisfying them all at the same time.  In many parts of the world, maize has to keep on providing an affordable subsistence crop for rural communities.
 
In the European Union, agriculture has the following duties:
     - to maintain food autonomy
     - to give preference to local produce
     - to play an active role in improving the living environment, while contributing to the preservation, or if need be restoration, of the natural environment.

Germination:  the radicle (taproot) breaks through the seed coat (or tegument).
Emergence:  the first leaf appears on the surface of the soil, and the seedlings form a row.

The terminal bud grows and turns into the tassel (male flower) which emerges from a cone of leaves.
One or more axillary buds turn into the ears (female flowers);  the plant starts silking.

The silks extend outside the ear.  The tassel produces pollen.  The ovules are fertilised.  By then the leaves have completed their growth.

The silks turn brown.  The fertilised ovules become kernels and grow larger – the kernel filling stage.  They store carbohydrates (starch), protein and lipids.  As they lose moisture, they gradually go through a milk stage to a dent stage (as dry matter accumulates).

Silage maize is harvested when the entire plant has dry matter content between 32 and 35%.  The whole plants are milled and stored away from air and light, beneath plastic sheeting.
 
Grain maize is harvested with a moisture content between 25% and 35%.  The grain is then dried to bring the moisture down to 15% before being marketed.
 
Sweet corn is harvested with a moisture content of 70-72% after growing for approximately 90 days and is then processed in the food industry (canned or frozen) or sold as corn on the cob.