If the stories of Adam and Noah are real historical events, referenced by Jesus, incest must’ve been committed to produce society as it is today. But, in the Bible incest is forbidden and from a secular view point is extremely immoral

Because Adam and Eve were the first human pair, their children necessarily married close relatives in the earliest generations. Genesis says that Adam “begat sons and daughters” (Genesis 5:4). Cain’s wife, therefore, would have been a sister or another close relative from Adam and Eve’s growing family.

This was not a violation of God’s law at that time because the specific prohibition against marriage between close relatives had not yet been given. Those restrictions were later clearly established in the law of Moses (Leviticus 18:6–18), after the human population had greatly increased.

After the Flood, Noah’s three sons already had wives (Genesis 7:7), so humanity restarted with four married couples. Their descendants would still have married within the extended family for a time, but as the population grew, increasingly distant relationships became possible.

The later biblical prohibition against incest does not create a contradiction. God permitted close-relative marriage when it was necessary for the continuation of the human race, but He later prohibited it when it was no longer necessary.

There may also have been biological reasons for this change. Today, close-relative reproduction carries a greater risk of inherited genetic disorders because harmful recessive traits are more likely to be expressed. Scripture does not explicitly give genetics as the reason for the prohibition, so this should not be presented as certain, but it is consistent with the protective nature of God’s law.

From the biblical perspective, then, close-relative marriage occurred during humanity’s earliest generations because there were no unrelated people available. It was a unique condition at the beginning of human history, not a permanent moral pattern.

Once humanity had multiplied, God expressly forbade incestuous relationships, and those prohibitions remain consistent with the broader biblical principles of sexual purity, family order, and protection from harm.