Recent developments in genetic engineering have increased human control over these traits. Merely creating a weed free, irrigated and well fertilized environment does not change the fact that a corn plant takes a certain amount of time to germinate and matures on a seasonal time-table. Similarly, fruit in an apple orchard may ripen over a time span that is not conducive to quick and efficient harvesting.
Plant breeders form gene combinations which enhance certain desirable traits by breeding hybrids.
Hybrids are created by crossing two plant varieties and growing the resulting seed. The major crop varieties available today have been bred to ripen at the same time, thus making harvesting more efficient. In order to increase shipability, these varieties tend to have tough skins. They are also bred for uniformity of size so they will pack easily into boxes. Genes which enhance drought tolerance or resistance to certain diseases can also be added to varieties.