Crossbreeding is the process of producing offspring from parents who originate from different species, varieties, or regional populations. Used to create new varieties with beneficial characteristics from both parents, the offspring are often bred to have better vigor than either parent, along with a specific number of desired traits. While crossbreeding is primarily used in farming to produce heartier crops and livestock, irresponsible crossbreeding can result in weak offspring that dilute the purebred population.
Most domestic animals have been crossbred. While many may be from a mixed heritage background that resulted in animals whose parentage is unknown, farm livestock is carefully bred to ensure that desired genetic traits are passed in combination to offspring. For example, cattle in particular have been bred for specific reasons such as increased milk yield, or larger beef production.
An immense variety of sheep species has been produced by crossbreeding, allowing individual farmers to achieve goals such as better coats for wool, larger sizes for meat, or better fertility. One of the oldest hybrid species in the world is that of the mule, the offspring of a female horse and a male donkey. Mules have been used for centuries as animals of hard labor, and are said to be less obstinate and faster than a donkey and longer lived and hardier than horses.
Much like animals, plants have been subjected to crossbreeding, as well. Producing plant hybrids can help to create a species that has a higher resistance to disease and has an increase in yield. Corn in particular has been the subject of large amounts of crossbreeding, with experts aiming for a species that is far better in terms of food production than any of its parent varieties. With the process of domestication believed to have begun between 7,500 and 12,000 years ago, corn is now one of the most common and diverse crops that is used in modern agriculture with millions of tons produced every year.
Most crossbreeding is carried out to benefit the offspring and to fulfill human needs. Humans have, for example, produced bigger and heartier livestock for food consumption; a multitude of dog species for hunting, guarding and friendship; and millions of plant species that resist disease, populate gardens with beautiful flowers, and produce a range of food sources. Some crossbreeding in animals, however, has resulted in detrimental effects alongside beneficial ones. Cattle used for milk production sometimes have high rates of cystitis due to constant and high milk-production schedules. Race horses can face death if they break a limb due their modern physique, while dog species such as Bulldogs and Pomeranians face breathing difficulties due to crossbreeding for shorter snouts.