A reader writes:

Dear Mr. Jay Rogers,

I have a question on ethics that I am hoping that you can clarify for me. The question is on sexual ethics and is in reference to incest. Could you explain to me how we as Christians can claim a universal and absolute standard of morality in the realm of sexual ethics when God created both male and female and there was interbreeding between direct family members until the prohibition later in the Law of Moses? How can we claim that moral absolutes are universal, abstract and invariant and an extension of God’s character when this prohibited sexual practice was the original design for God’s created order?

From looking at the situation throughout the whole of creation and salvation-history, and considering the fall of mankind into sin, I understand that it is sin that has corrupted the practice of any and all sexual acts. Thus, it would not be God’s standard that has changed but rather, the standard of a fallen world that has changed. Just like in pre-fall where mankind was naked and not ashamed, it would be the same for sexual ethical practices. Am I on the right track here and could you please give me your opinion and wisdom on this topic if you get the chance? Any help in this area would be greatly appreciated. May the Lord Jesus Christ bless you and yours always.

- J.K.

Dear Mr. J.K.,

Incest between brother and sister, and one’s parents, aunts, uncles, grandparents, etc., is prohibited by the law of Moses. This prohibition also included in-laws in all but one case, that of a brother marrying his deceased brother’s wife.*

Marriage between first cousins is allowed.

However, it is implied in scripture that Seth and Cain married one of the daughters of Adam. Obviously that would be their sister. The Bible account says Adam became father to “sons and daughters.”

“And the days of Adam after he had begotten Seth were eight hundred years and and he begot sons and daughters” (Genesis 5:4).

The Bible further tells us that Eve was the mother of all living people. So it was a natural sister.

There are two ways of looking at this. Both ways include your point of view.

1. The sin of incest is a product of the Fall of Adam.

We are all products of a sinful man and carry original sin. The consequence is that all of Adam’s grandchildren were conceived in the sin of incest.

“And Adam lived one hundred and thirty years, and begot a son in his own likeness, after his image, and named him Seth” (Genesis 5:3).

Even as Seth was in Adam’s fallen image and likeness, so also are every one of us. We are all sons and daughters of Adam, born in sin even as Adam was fallen. It is redundant to say it, but every person since then has been born in Enosh’s image and likeness (Seth’s son) who himself was a product of incest.

This sin would have produced a curse on all mankind, just as the Moabites and Ammonites were accursed due to an incestuous beginning between Lot and his daughters.

However, the curse can be reversed after several generations of continued obedience to God’s moral law. Let’s not forget that Jesus himself was a product of incest (Tamar and Judah). He was also the product of a Gentile (Ruth and Boaz); a prostitute (Rahab and Salmon); and adultery (Bathsheba and David). Thus Jesus’ genealogy mentions only four women. These were four unions that, according to the law, were not supposed to happen. I believe these marriages are purposefully listed to show that redemption occurs after several generations. The curse is lifted eventually. This is meant to be a type of the curse of original sin being destroyed once and for all by Christ.

One solution to the problem is to admit unlawful incest with the union of Adam’s children and that it was part of the curse. But the debt of sin has been redeemed by Christ.

We could also conculde that since many years passed between Cain’s birth and the arrival of Seth’s first child, Enosh, that Seth could have married one of Cain’s descendants.

“And Adam lived one hundred and thirty years, and begot a son in his own likeness, after his image, and named him Seth. After he begot Seth, the days of Adam were eight hundred years; and he had sons and daughters. So all the days that Adam lived were nine hundred and thirty years; and he died. Seth lived one hundred and five years, and begot Enosh” (Genesis 5:3-6).

Genesis records that 235 years passed between the creation of Adam and the birth of Enosh. Genesis does not record how old Cain was when he had his first son. However, if Cain was born early on in this chronology and began having children at a young age, then even though Cain was forced to marry his sister as a result of the Fall, Seth would have had had the opportunity to marry a grand-grand-niece, a relative further removed than a first cousin, a union not prohibited later on by the law of Moses. One could argue that the line of Cain was much more prolific than the line of Seth in light of the fact that only eight righteous people from Seth’s line, Noah’s family, survived the Flood. It is not impossible that the curse of incest affected only the line of Cain.

In contradiction to this, Jewish folklore preserved in the apocryphal Book of Jublilees (which is not to be considered inspired or inerrant) tells us that each patriarch in the line of Adam took a sister to be his wife until the fifth generation of Mahalalel when men began marrying their cousins and distant relatives.

2. The prohibition against incest occurred only after the days of the Flood.

The law against incest was not originally instituted by Moses. We see that even before Moses, Abraham deceived Pharaoh into thinking that Sarah was his sister, and therefore could not be his wife. So we know that by Abraham’s deception, marriage with an immediate sibling was unlawful even prior to Moses. We also see Judah recognizing his sin when he discovered that he had committed incest with his daughter-in-law, Tamar.

It is possible that this covenantal shift took place only after the days of Noah. That would not be unprecedented, since there are several provisions of the law that changed after the Flood. When Cain slew Abel, God did not allow him to be found and killed (Genesis 4:15). However after the Flood, God did not allow a murderer to go unpunished by execution (Genesis 9:6). Prior to the Flood men were vegetarians (Genesis 1:29). After the Flood they are given the flesh of clean animals to eat and enmity between man and beast was established by God himself (Genesis 9:1-3).

If the laws concerning homicide and the relationship between men and animals changed after the Flood. It is therefore logical that the relationships between family members may also have been changed. Just as the laws concerning what foods we may eat have become more liberal — for example we are no longer constrained not to eat unclean animals under the New Covenant — the laws governing marriage have become more strict.

Prior to the Flood the gene pool would have been much more divergent than it is today. For example, I had a discussion with an atheist recently about Neanderthal man. Some scientists claim that recent DNA studies show that Neanderthal was not an ancestor of modern man. I argued that nothing would preclude him from being a descendant of Adam, a subspecies of Homo sapiens whose line was cut off. It is conceivable that there were many other varieties of man prior to the Flood that were far more diverse than today.

I’ve also had atheists argue that this union of Seth and his sister would have been impossible since it would have resulted in a human race with massive birth defects; that the gene pool from two people wasn’t large enough to account for the diversity we see today; and so on. But we can assume that the genetic information in Adam and Eve was capable of producing a much more diverse population than exists today, because after the time of Noah, all humanity was reduced to the genes of just six people. Noah’s grandchildren would have had only the opportunity to marry their cousins. Since the gene pool became more limited, the marriage between brother and sister suddenly would have had a more negative effect and therefore was prohibited.

We might also look at “sin” from a practical point of view. The Bible says all unrighteousness is sin (1 John 5:17). According to Strong’s, the word “unrighteousness” in Greek is adikia:—(legal) injustice (properly the quality, by implication the act); moral wrongfulness (of character, life or act):—iniquity, unjust, unrighteousness, wrong. So the word “unrighteousness” simply means something that is not right for us.

Why is sin not right? The legalistic way of looking at it is that God arbitrarily decided that certain behaviors are sinful and therefore wherever there is a law against something, there is sin; and wherever the law is silent there is no sin. Nothing could be further from the truth. Sin is unrighteous because it results in death. And there are many things that are obviously sinful that are not mentioned in the Bible. These can be derived from principles in the Bible, but there is no law prohibiting them.

For instance, many people think it is lawful to be addicted to tobacco, to gamble, to smoke marijuana, and to commit abortion because these things are not specifically prohibited by civil law or by biblical law. I would argue that all of these are sinful because they each lead to death.

However, if something does not result in death, it is not sin. For instance, it would be unlawful to jump off a cliff because you would die, and God forbids homicide. However, to jump off a cliff with a parachute would not be unlawful, foolish perhaps, but not a violation of the sixth commandment necessarily. In the same way incest between a brother and a sister would not be unlawful if there is no natural harm done — if it did not result in death. Since there was no harm done to the human race by the union of Seth and his sister, then there was no sin involved.

I hope that answers your question.

This isn’t meant to open a can of worms, but theonomists also ought to explain why the Levirite marriage is no longer in effect. Among the Hebrews marriage with a brother’s widow was forbidden as a general rule (Leviticus 18:16; 20:21), but was regarded as obligatory (Deuteronomy 25:5,6) when there was no male offspring, and when the two brothers had been dwelling on the same family estate. (This is actually an easy one.)