Science in the Bible – Don’t Marry Kin

(3 Minute Read)

Early in human history men married sisters, nieces, and close relatives. At the very beginning of history, there was no one else to marry. Adam’s sons had to marry close kin in order to ensure the continuation of the human race.

Adam and Eve had many sons and daughters as they obeyed God’s command to be fruitful and multiply and fill the earth (Genesis 1:27-28).

Adam lived to age 930, so he could have had hundreds of sons and daughters.
Then the days of Adam after he became the father of Seth were eight hundred years, and he had other sons and daughters. (Genesis 5:4)

Many of Adam’s sons married sisters, and other sons married nieces or grand-nieces to begin filling the earth. How else could two people carry out God’s command, “Be fruitful and multiply, and fill the earth” (Genesis 1:28)? If brothers had not married sisters, mankind would have died out in one generation.

Later after Noah’s Flood, men again had to marry close relatives (like sisters and cousins) until the population built up.

Today boys are repulsed by the idea of marrying their sisters. Adam’s sons and Noah’s grandsons did not have that option. No one existed for them to marry except close relatives like sisters, nieces, or cousins.

There was no reason for Adam’s sons to feel reluctant to marry their sisters. Cain and his siblings were first-generation offspring of Adam and Eve. Even for generations thereafter the gene pool was relatively clean. Enough harmful genetic errors had not accumulated in the DNA to make marrying close relatives unwise. This danger developed as the consequences of human sin compounded over the years.

Today degeneration of the gene pool has intensified. Marriage between close relatives now risks severe problems in the offspring when identical defective recessive genes occur in both closely related parents, with the deleterious trait being passed on to children. The more inbreeding occurs, the more birth defects appear.

Restrictions against marrying close relatives did not exist until the time of Moses, 2500 years after Creation. In early generations the restriction was unnecessary. Adam himself married a closer relation than anyone else ever has, for Eve was bone of his bones and flesh of his flesh (Genesis 2:23). Eve was practically a clone of Adam, having been made from his rib. Noah’s grandchildren married siblings or cousins. Abraham and Isaac each married close relatives (Genesis 20:11-13; 11:27; 24:47-51, 67).

But the acceptability of marriage to close relatives changed with the Law given to Moses on Mt. Sinai shortly after the nation of Israel left Egypt. Yahweh told Moses,
“You shall not do what is done in the land of Egypt where you lived, nor are you to do what is done in the land of Canaan where I am bringing you; you shall not walk in their statutes. You are to perform My judgments and keep My statutes, to live in accord with them; I am the Lord your God. So you shall keep My statutes and My judgments, by which a man may live if he does them; I am the Lord. None of you shall approach any blood relative of his to uncover nakedness; I am the Lord.” (Leviticus 18:3-6 NASB)

Leviticus 18 continues by detailing all the forbidden close-kin marital relationships. Then Yahweh concludes with
“Do not defile yourselves by any of these things; for by all these the nations which I am casting out before you have become defiled. For the land has become defiled, therefore I have brought its punishment upon it, so the land has spewed out its inhabitants. But as for you, you are to keep My statutes and My judgments and shall not do any of these abominations, neither the native, nor the alien who sojourns among you (for the men of the land who have been before you have done all these abominations, and the land has become defiled); so that the land will not spew you out, should you defile it, as it has spewed out the nation which has been before you. For whoever does any of these abominations, those persons who do so shall be cut off from among their people. Thus you are to keep My charge, that you do not practice any of the abominable customs which have been practiced before you, so as not to defile yourselves with them; I am the Lord your God.” (Leviticus 18:24-30 NASB)

At the time when Yahweh forbid consanguineous marriage for Israel, it was common practice in Egypt and Canaan. Not only were sibling marriages common, but incestuous relations between parents and children were frequent. These were common practices in Moses’ day. (Leviticus 18:3, 24-30; 20:23)

Austrian monk Gregor Mendel (1822-1884) is considered to be the founder of modern genetic science. But around 1450 BC, long before genetic science understood the reason for the prohibition of close-kin marriage, the Bible prohibited it. The Law of Moses prohibited incestuous relations on pain of death, ostracism, and barrenness (Leviticus 20:11-12, 14, 17, 19-21, 23).

Science Catches Up to the Bible

The Bible’s wise prohibition of close-kin marriage was the basis for marriage laws throughout Christian lands, even before science understood the reasons for the prohibition. Although the Bible is not primarily a science textbook, it does contain many scientific truths like this one and like those mentioned in this Science in the Bible series, truths that long pre-date their discovery by today’s scientists. This is strong evidence of divine authorship of the Bible.

Questions to Ponder

1. How can you be salt and light so that incest does not become fashionable, as has happened with other sexual perversions?
2. How is the demand for easy abortion access related to our culture’s rejection of Scriptural morality?

Share your thoughts on these questions in the comments below. It could encourage or help another reader.

Soli Deo Gloria.

This is the seventh in the Science in the Bible series of blog posts. While there is much science connected with Creation and Noah’s Flood, this series will focus on lesser known scientific truths that were alluded to in the Bible long before they were known to scientists.
Read the prequels:
1. Science in the Bible – Blood
2. Science in the Bible – Ocean Currents
3. Science in the Bible – Undersea Mountains
4. Science in the Bible – Ocean Reservoirs
5. Science in the Bible – Good Medicine
6. Science in the Bible – Round Earth

Read the sequel:
8. Science in the Bible – Fearfully and Wonderfully Made

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©William T. Pelletier, Ph.D.
“contending earnestly for the faith”
“destroying speculations against the knowledge of God”
“for the defense of the gospel”
(Jude 1:3; 2 Cor 10:5; Phil 1:16)
Wednesday March 15, 2017 A.D.

Thy word is a lamp to my feet and a light to my path. (Psalm 119:105)