Answer: Humanity’s moral standards change with time.
Step-by-step explanation:
Humanity’s moral standards have changed through history, and from culture to culture. Let´s think of one of the most condemnable acts in most current societies: incest. It´s a cultural taboo in most civilizations.
However, incestuous marriages were normal throughout the Graeco-Roman period of Egyptian history. Furthermore, European royal families looking for intermarriages that could strengthen political alliances ended up becoming extremely inbred.