 Domestication is a sustained multi-generational relationship in which one group of organisms assumes a significant degree of influence over the reproduction and care of another group to secure a more predictable supply of resources from that second group. Charles Darwin recognized the small number of traits that make domestic species different from their wild ancestors. He was also the first to recognize a difference between conscious selective breeding in which humans directly select for desirable traits, and unconscious selection where traits evolve as a by-product of natural selection or from selection upon other traits. There is a genetic difference between domestic and wild populations. There is also such a difference between the domestication traits that researchers believe to have been essential. That was the early stages of domestication, and the improvement traits that have appeared since the split between wild and domestic populations.Domestication traits are generally fixed within all domesticates, and were selected during the initial episode of domestication of that animal or plant, whereas improvement traits are present only in a proportion of domesticates, though they may be fixed in individual breeds for regional populations. The dog was the first domesticated vertebrate, and was established across Eurasia before the end of the late Pleistocendera, well before cultivation and before the domestication of other animals.The archaeological and genetic data suggest that long-term bi-direction botanical gene flow between wild and domestic stocks, including donkeys, horses, new and old world camels, goats, sheep, and pigs, was common.712 given its importance to humans and its value as a model of evolutionary and demographic change, domestication has attracted scientists from archaeology, paleontology, anthropology, botany, zoology, genetics, and the environmental sciences.13 Among birds, the major domestic species today is the chicken, important for meat and eggs, though economically valuable poultry include the turkey, guinea fowl and numerous other species. Birds are also widely kept as cage birds, from songbirds to parrots. The longest established invertebrate domesticates are the honeybee and the silkworm. Terrestrial snails are raised for food, while species from several filet are kept for research, and others are bred for biological control. The domestication of plants began at least 12,000 years ago with cereals in the Middle East, and the Bottle Gourd in Asia. Agriculture developed in at least 11 different centers around the world, domesticating different crops and animals.