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
Human uses of birds whereas an antelope can yield as much as 31,000 kcal/hour, and wild rye around 1,000 kcal/hour. Birds have been domesticated and bred as poultry for use as food for at least four thousand years. The most important species is the chicken. It appears to have been domesticated by 5000 BC in northeastern China, likely for cockfighting, and only later used for food. In ancient Egypt, poultry including ducks, geese, and pigeons were captured in nets and then bred in captivity. Chicken now provides some 20% of the animal protein eaten by the world's human population in the form of meat