evolution.berkeley.edu/.../images/cornfld.jpg

Long before recorded history, people were modifying plants to make them useful as food crops. At the top left is a wild grass plant called teosinte. It is a very close relative of our modern corn plant with is huge ear to which the kernels stick so tightly that we can collect the whole package of nourishment with a machine. These two plants look so different that when teosinte was discovered, people thought it belonged to a different species than corn. But these plants are such close relatives that they can be crossed, producing seeds that can grow and have a variety of reproductive structures. Teosinte produces its seeds at the tops of its shoots like other grasses. The seeds, seen above on the right, are rock hard -- they have silica deposits in the surface layer. Wild seeds need to survive intact through a bird’s or an animal’s digestive tract. They’re just along for the ride, counting on the consumer to disperse the seed, generally depositing them in a new place with a bit of fertilizer. Most importantly, the teosinte plant’s seeds structure flies apart when it is mature to scatter the seeds. The technical jargon for this is a disarticulating rachis, which is what this structure is called. The first thing people selected for were plants with a non-disarticulating rachis -- one that doesn’t fly apart. The genetic transformation of teosinte to our modern corn plant is perhaps humankind’s most extraordinary feat of genetic engineering. The great expansion in the size of the seed structure, the ear, happened largely in the 20th century. Very early in the century, geneticist George Harrison Schull (http://en.wikipedia.org/wiki/George_Harrison_Shull) discovered that when he inbred corn, the plants got rather small, as did the ears. But when he crossed two inbred lines, the first hybrid generation produced much larger plants with large ears than either parent plant. This is how today’s highly productive hybrid corn is still produced.