Offerings to the gods are artifacts of the agricultural revolution.
Once man becomes a partner in the cultivating, creative act it becomes important for him to ratify that partnership by recognizing the gods' role in the enterprise. So long as the people were merely hunter/gatherers and not cultivators their gratitude to the gods was of a different order. Hunter/gatherers did not sacrifice, they merely paused to thank the source of the animal’s life, which life was about to be ended for the sake of the hunter’s sustenance.
Sacrifices, on the other hand, were actually reciprocations for the gift of providence the harvest had already demonstrated.