If we all descended from one man and one woman then it's quite apparent that a third generation was not possible without the sexual union of close relatives.

Does the Bible (or other Christian source) specifically address incest? Is it a sin?

If it is not a sin then does it follow that it is not practiced in Christianity for purely secular reasons?

If it is a sin should the children of Adam and Eve not have reproduced?

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    I always enjoy pointing out that it's not just Adam and Even, but also Noah. If you follow strict belief of the bible, anyone between Adam and Noah was wiped out except for Noah, his wife, and his descendants.
    – Richard
    Commented Sep 6, 2011 at 12:51
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    @Richard Noah's three sons and their wives were all on the ark. There's no mention of Noah having any daughters. Noah's grandchildren could have been marrying their cousins, not necessarily committing incest.
    – jimreed
    Commented Sep 6, 2011 at 13:54
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    This question appears to be off-topic because it is about "Is X a Sin" This is an older question that predates the guideline, but it wouldn't pass muster today. Commented Sep 26, 2013 at 19:25
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    This should bot be closed. It is because it causes uncomfortable conversation. I apologize that it is closed and closing it merely stifles honest input. Indeed you can tell from votes and comments that this is a fair topic.
    – user13599
    Commented Dec 12, 2015 at 23:56
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    This is a valid question. I've nominated it for reopening. St. Thomas Aquinas answered it in his Summa Theologica II-II q. 154 a. 9.
    – Geremia
    Commented Dec 13, 2015 at 1:45

5 Answers 5


The OT clearly condemns in Leviticus 18 and 20 ("If a man takes his sister [...] and sees her nakedness [...] it is a disgrace [...] and he shall bear his iniquity."). This is reinforced at other later points, but we do not find record or such a prohibition earlier.

Clearly there is no way that the line from Adam and Eve continued for at least the first few generations without some in-marrying.

We know from science today that in-breeding makes for bad genes. Perhaps in the early days when things were a little bit less degenerate physically (and people were living to their 900's) God allowed such a practice, but as the gene pool grew and there was no need for it, he introduced a prohibition for our own good. Clearly today it would be a sin of disobedience against God.

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    So there is a clear contradiction in the Bible, and you resolve that with speculation. Perhaps in the early days God allowed such a practice If the Bible is sacred, there's no room for speculation.
    – siamii
    Commented Sep 6, 2011 at 13:19
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    @bizso09: No there is no contradiction here. The Mosaic law in Leviticus had lots of things which were not previously commanded or requested of God's people just like in the NT we see things asked of believers (e.g. Baptism) that were not required in the OT.
    – Caleb
    Commented Sep 6, 2011 at 13:33

It is written in Leviticus 18:6 that it is a sin -

None of you shall approach any one of his close relatives to uncover nakedness. I am the LORD.

and in 1 Corinthians 5:1 -

It is actually reported that there is sexual immorality among you, and of a kind that is not tolerated even among pagans, for a man has his father's wife.

The reason that it was not a sin for the children of Adam and Eve was at the time, the law had not yet been established.

  • Would the law have come into existence at some point before the timeframe of Leviticus/Corinthians, or specifically at the time the commandments were given to Moses? Commented Sep 6, 2011 at 8:03
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    Like any law, it is not enforced until it is established. This is true even for retro-active laws: the act is legal until it is outlawed.
    – Richard
    Commented Sep 6, 2011 at 15:08

As regards the children of Adam and Eve, the narrative of Cain suggests in at least three places that there were other people on Earth at his time:

First, in Genesis 4:14-15, he worries that he will encounter people who will want to kill him, and God gives him a mark of protection.

Second, he then moves to Nod, at which point he has a wife (Gen. 4:16-17). The wife is presumably not a child of Adam and Eve, as we do not hear of any other children being born after Abel until Seth, which is mentioned after six generations from Cain (Enoch, Irad, Mehujael, Methushael, Lamech, and Lamech's sons, Gen. 4:17-25). The birth of Seth comes when Adam is 130 years old, and daughters and other sons followed on after that (Gen. 5:3-4), while Cain is implied to be born very shortly after the Fall.

Third, Cain builds a city in Nod (Gen. 4:17), which assumes a community of some size already existing.

The only place in the creation narrative where it suggests only two humans were ever created is Genesis 3:20, "Now the man called his wife's name Eve, because she was the mother of all the living"—and this in itself does not look like a literal statement, as at that point she had not yet, in fact, given birth to anyone.

(Certainly it looks like only two humans were put in Eden; in the Elohist account, though, we have that male and female humans were created on the sixth day (Gen. 1:27) and their number is not specified, at least in the usual English translations.)

  • Pope Pius XII stated (as official dogma) that all are descended from Adam. So for the Catholics, this option is not allowed. Commented Dec 28, 2011 at 15:21
  • @Marc Interesting! Are the antediluvians included in that 'all', or only people of the present age? As Noah was descended from Adam, everyone born since the Flood would indeed be descended from Adam as well, whether there were non-Adamic people before the Flood or not.
    – Muke Tever
    Commented Dec 28, 2011 at 16:40
  • My understanding is "all", but - not my specialist subject Commented Dec 28, 2011 at 16:43
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    It's been pointed out to me that if there were other people not descended from Adam, they would not have been subject to original sin, and this might have theological consequences to the idea. (Though the two types of people might be one explanation of the 'sons of God' vs 'daughters of men' in Gen. 6:2 and 6:4.)
    – Muke Tever
    Commented Dec 28, 2011 at 16:45

You are all over-complicating things. Here's how it happened:

God created Adam, and then Eve. (Genesis 1:27-28; 2:22)

God then told them to be fruitful and multiply (make love and have children) (Genesis 1:28) [Note that Genesis tends to jump around a little chronologically]

Now, the gene pool then was so pure (sin isn't here yet) that Adams offspring were able to interbreed and not have any defects at all. Presumably to the point up until God outlawed it in Deuteronomy 27:22-23 and other passages. Obviously the gene pool started to grow causing more and more defects with each inbred child.

It's clearly a sin because:

  1. God outlawed it in the OT

  2. And it is apparently appalling to Paul when he learns of a man sleeping with his mom in 1 Corinthians 5:1, thus implying that the act is still outlawed and not acceptable in Gods eyes.

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    Sorry, the gene pool would've been pure because they were the very first humans. Not because sin wasnt there. Sorry, my error.
    – Mason
    Commented Jul 9, 2013 at 3:37

It is, indeed, a sin, as the ones who answered before me have pointed out it is said in the Scripture. But incest was permitted from the creation of man until the giving out of the laws to Moses. In the time before that, humanity was in its 'young age'.

It's like when a parent only imposes the first rules on his child when he is old enough to need and to understand them.

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