Ever since humans have started planting seeds and harvesting crops, they have unconsciously been selecting some traits of the plants over other traits. This selection process involved nothing more than rejecting the crops that were not suitable for consumption, or had low yield, and using those which were good/easy to eat, and easy to harvest. Over thousands of years, this process has helped domesticate a number of plants, which cannot survive in the wild today and are totally dependent on our abilities as harvesters for their survival.

Corn: Past and Present (Courtesy: PhysOrg)One prime example is the corn (or maize) plant. Corn has been one of the primary crops since antiquity. The North American corn is a direct descendant of a grass called Teosinte, which is found in Mexico, Guatemala and Nicaragua. Researchers have now identified corn genes that were preferentially selected by Native Americans during the course of the plant's domestication.
The corn was domesticated about 6,000 years ago. Out of its 59,000 genes, about 1,200 were preferentially selected during this domestication process. The domesticated corn lost the ability to survive in the wild, produced larger and softer yields, and survived much longer:).
The study was published by University of California, Irvine's Brandon Gaut and his colleagues in the journal Science. Gaut and his coworkers used relatively new genomic techniques to determine the DNA sequence of 700 gene bits in the two plants (modern corn, and ancstral Teosinte) and used population genetics, the study of genetic variation, to compare them.
According to the scientists, the will provide important insights to modern corn breeders in their quest to establish hardier, higher-yielding corn plants. The scientific approach will also be useful in the study of other domesticated organisms, plants and animals alike, and will help us understand the natural processes by which plants and animals were once domesticated by our ancestors:).