According to the Bible all humans on Earth are descendants of Adam and Eve. Their children Cain and Seth create two separate lineages of human life on Earth. Cain and Seth must have had sexual intercourse with their mother Eve, or an unnamed sister to propagate humanity. This was not necessarily considered immoral because there was no other way to create children. | According to the Bible all humans on Earth are descendants of Adam and Eve. Their children Cain and Seth create two separate lineages of human life on Earth. Cain and Seth must have had sexual intercourse with their mother Eve, or an unnamed sister to propagate humanity. This was not necessarily considered immoral because there was no other way to create children. |