Quote from Leon Kass, Ethicist, from his book The Hungry Soul: Eating and the Perfection of Our Nature

“…nature does everything in the operations of a beast, whereas man contributes to his operations by being a free agent. The former chooses or rejects by instinct and the latter by an act of freedom, so that a beast cannot deviate from the rule that is prescribed to it even when it would be advantageous …