Animal genetic resources for food and agriculture crop and livestock species in the early neolithic time period changed our human evolution and lifestyles. This ability to control food production led to major demographic, technological, political and military changes. Consecutively, thousands of years of natural and human selection, genetic drift, inbreeding, and crossbreeding have contributed to the diversification of animal genetic resources and increased the variety of environments and production systems that livestock keeping takes place. Relatively few species have been domesticated; out of the world's 148 non-carnivorous species weighing more than 45 kg, only 15 have been successfully domesticated. The proportion of domesticated birds used for food
The Life of Birds only other species, but also cameras, a car alarm and a chain saw. Broadcast 2 December 1998, this programme discusses mating rituals. If a male bird is on the lookout for a partner and has a suitable nest, it must advertise the fact, either by its call, a visual display or both. The frigatebird provides an example of the latter, with its inflated throat pouch. The hornbill's courtship, among that of many others, also runs to the offer of a gift. For some species, dancing can also be an important component, and grebes are shown performing a "pas de deux".