Domestication involves both culture and biology. The cultural process of domestication begins when animals are incorporated into the social structure of a human community and become objects of ownership, inheritance, purchase and exchange. The morphological changes that occur in domestic animals come second to this integration into human society. The biological process resembles evolution and begins when a small number of parent animals are separated from the wild species and are habituated to humans. These animals form a founder group, which is changed over successive generations, in response to natural selection under the new regime imposed by the human community and its environment, and also by artificial selection for economic, cultural, or aesthetic reasons. In the wild, the evolution of a subspecies occurs when a segment of a species becomes reproductively isolated by a geographical barrier. With domestic animals, this separation leads to the development of different breeds.