We have exterminated unknown numbers of species, if not by hunting then by destroying their habitats to improve our own. Survivors of such disasters have repeatedly formed more conservative societies with less destructive values. Some American Indians, whose technology allowed only a marginal existence, did very well on the margins by teaching their children a reverence for life. They instilled the belief that all living things have a divine spirit and awareness like our own, and deserve cautious and respectful treatment. Societies everywhere tend to make virtues of their necessities, and to legitimize their values by invoking divine approval of them.
Mythologies supply plenty of awful examples of human failure to revere divinely protected life.
Among the many ironies of human existence, however, we have learned that nothing fails like success. The Aztecs too were barbarians whose rough simplicity won them an empire of astonishing wealth. Parvenus like the Romans and Aztecs still held reverence for life, but in a somewhat different form. Reverence, after all, is the attitude we should take to the holy. And if we are the gods' favorites, then human sacrifice is the greatest gift we can offer them.