Why this shift occurred is hard to say. Since the beginning describes all that was created in the Garden of Eden as good, including Adam and Eve, their genes may have been well-developed to the point that their kids could marry siblings and produce children with no genetic defects. This would fit the shift we see in Genesis from early generations with long lives producing children past their 100s to humans with shorter lives and shorter fertility rates. We go from Adam and Eve, who were still having children when they were over 100 years old (Seth was born when Adam was 130), to Abraham and Sarah who were past child-bearing age when Sarah was 90 and Abraham 100 years old (Genesis 17:17, 18:12). In Genesis 6:3, God decrees that humans will only live to be 120 years old, and other than a few patriarchs this holds true throughout the rest of the Bible. Regardless, God does forbid incest later (and then quite firmly) in the Bible. However we interpret who Adam and Eve’s sons married, we are left with the fact that the Bible doesn’t tell us every single bit of information we want. It gives us the facts we need and leaves us with reminders that whatever strange things people in the Bible did, God knew what he was doing and worked something good from it down the line.
- Genesis

© Clarencë mc