In common parlance, "devolution", "de-evolution", or backward evolution is the notion that a species can change into a more "primitive" form. It is associated with the idea that evolution is supposed to make species more advanced, and that some modern species have lost functions or complexity and seem to be degenerate forms of their ancestors. This view is rejected by modern evolutionary theory, in which adaptation arises from natural selection of forms best suited to the environment.

More than 50 billion chickens are reared annually as a source of food, for both their meat and their eggs.

The vast majority of poultry are raised using intensive farming techniques. According to the Worldwatch Institute, 74 percent of the world's poultry meat, and 68 percent of eggs are produced this way.

A common practice among hatcheries is the mass-slaughter of newly-born male chicks of egg laying breeds, since they don't lay eggs, and do not grow fast enough to be profitable for meat. Once separated from the females, the male chicks are dropped into grinding machines.

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