The Old Testament forbids incest. Does this aspect of the Mosaic law apply to Christians?

In the comments to this answer to the question of why Abraham lied to Pharaoh about his relationship with Sarah , the following question which I am about to pose, appeared: **Was the marriage between Abraham and Sarah incestuous?** In two separate occasions, Abraham told the local ruler that Sarah was his sister. These two passages are found in in Genesis 12:10-20 and Genesis 20 . Let's examine the first passage: Genesis 12:10-20 (NIV) > 10 Now there was a famine in the land, and Abram went down to Egypt to live there for a while because the famine was severe. 11 As he was about to enter Egypt, he said to his wife Sarai, “I know what a beautiful woman you are. **12 When the Egyptians see you, they will say, ‘This is his wife.’ Then they will kill me but will let you live. 13 Say you are my sister, so that I will be treated well for your sake and my life will be spared because of you.”** > 14 When Abram came to Egypt, the Egyptians saw that Sarai was a very beautiful woman. 15 And when Pharaoh’s officials saw her, they praised her to Pharaoh, and she was taken into his palace. 16 He treated Abram well for her sake, and Abram acquired sheep and cattle, male and female donkeys, male and female servants, and camels. > 17 But the LORD inflicted serious diseases on Pharaoh and his household because of Abram’s wife Sarai. **18 So Pharaoh summoned Abram. “What have you done to me?” he said. “Why didn’t you tell me she was your wife? 19 Why did you say, ‘She is my sister,’ so that I took her to be my wife? Now then, here is your wife. Take her and go!”** 20 Then Pharaoh gave orders about Abram to his men, and they sent him on his way, with his wife and everything he had. This seems to imply that since Abraham told Pharaoh that Sarah was his sister, Sarah was believed to be his sister only and not his wife. This, in turns, makes me draw the conclusion that marriage between siblings was unusual. Let's head on to the second passage: Genesis 20 (NIV) > 1 Now Abraham moved on from there into the region of the Negev and > lived between Kadesh and Shur. For a while he stayed in Gerar, **2 and > there Abraham said of his wife Sarah, “She is my sister.” Then > Abimelek king of Gerar sent for Sarah and took her.** 3 But God came to > Abimelek in a dream one night and said to him, “You are as good as > dead because of the woman you have taken; she is a married woman.” > > 4 Now Abimelek had not gone near her, so he said, “Lord, will you > destroy an innocent nation? **5 Did he not say to me, ‘She is my > sister,’ and didn’t she also say, ‘He is my brother’? I have done this > with a clear conscience and clean hands.”** > > 6 Then God said to him in the dream, “Yes, I know you did this with a > clear conscience, and so I have kept you from sinning against me. That > is why I did not let you touch her. 7 Now return the man’s wife, for > he is a prophet, and he will pray for you and you will live. But if > you do not return her, you may be sure that you and all who belong to > you will die.” > > 8 Early the next morning Abimelek summoned all his officials, and > when he told them all that had happened, they were very much afraid. 9 > Then Abimelek called Abraham in and said, “What have you done to us? > How have I wronged you that you have brought such great guilt upon me > and my kingdom? You have done things to me that should never be done.” > 10 And Abimelek asked Abraham, “What was your reason for doing this?” > > 11 Abraham replied, “I said to myself, ‘There is surely no fear of > God in this place, and they will kill me because of my wife.’ **12 > Besides, she really is my sister, the daughter of my father though not > of my mother; and she became my wife. 13 And when God had me wander > from my father’s household, I said to her, ‘This is how you can show > your love to me: Everywhere we go, say of me, “He is my brother.”’”** > > 14 Then Abimelek brought sheep and cattle and male and female slaves > and gave them to Abraham, and he returned Sarah his wife to him. 15 > And Abimelek said, “My land is before you; live wherever you like.” > > 16 To Sarah he said, “I am giving your brother a thousand shekels[a] > of silver. This is to cover the offense against you before all who are > with you; you are completely vindicated.” > > 17 Then Abraham prayed to God, and God healed Abimelek, his wife and > his female slaves so they could have children again, 18 for the LORD > had kept all the women in Abimelek’s household from conceiving because > of Abraham’s wife Sarah. This second passage also tells us that marriage between siblings was unusual. It also tells us that Abraham did not really lie when he said that Sarah was his sister, since she was his half-sister. *Also note that nowhere in the two passages Abraham is accused of lying!* This is a quite interesting fact. In any way, it is clear that our definition of incest in today's western society, is not the same as it was in that time and place. Still, Deuteronomy 27:22 clearly states that for a man to marry his father's daughter (as Abraham did) is a sin! How does one reconcile these passages? Was Abraham's and Sarah's marriage a sin? Was it considered incest?

My question, in strict propriety, is specifically what kind of relationships are defined as incestuous in Christianity? I am guessing that it is forbidden to marry one's parents/children or siblings but what about other relations like first cousins. I would appreciate some sort of a reference to maybe a specific passage in Christian holy scriptures. Is this something specifically commanded by God explicitly, listing forbidden relations? Or is it some sort of an interpretation done later by a scholar which is widely accepted today? And I am talking about Christianity in general encompassing all of its sects. Do different sects have different rules?

Leviticus 18:7 states: "Do not violate your father by having sexual relations with your mother. She is your mother; you must not have sexual relations with her." **Isn't saying that the old law is "done away with" by logic, giving an excuse to say that people can now have sex with their mother?** Leviticus 18:23 states: “A man must not defile himself by having sex with an animal. And a woman must not offer herself to a male animal to have intercourse with it. This is a perverse act. **If the old law is "done away with" then doesn't this also mean by logic, that bestiality is now okay?**

I have a multi-part question. - Did Adam and Eve's Progeny Commit Incest? Genesis, Chapter 4 tells us about Cain and Abel. Genesis, Chapter 5 tells us about Seth and "other sons and daughters". I highly doubt that our species began with many acts of incest (not just for religious/legal/moral reasons but biological reasons as well), so how did humanity continue? As a Christian, am I obliged to accept one of the following? 1. Adam and Eve's progeny mated with descendants from another lineage that the Bible (through no apparent malice) failed to describe. 2. The story of Adam and Eve is just that - A story. It is a story that was passed down by way of oral tradition. It was never meant to describe actual historical events.

According to the Genesis 19:30-38 , when *Lot* escaped out of *Zoar*, he went up to the mountains and settled in a cave. While in there, his daughters seduced him while he was drunk so that they could bear children and save their family line. Does this mean saving one's family line is/was so important that you could have sex with your own offspring? Was Lot really drunk to a point that he didn't know what he was doing? Were the daughters wrong to do it? If so, why didn't Lot take any action afterward?

I may not be asking the right question, but I'm trying to figure out the context behind a quote from [an Arthur Pink sermon](http://www.pbministries.org/books/pink/Sermon/sermon_06.htm) : > herein we may see the blasphemous impiety of the popes of Rome, who in the canons have dared to dispense with some of the laws of consanguinity in [Leviticus 18](https://www.biblegateway.com/passage/?search=leviticus+18&version=NABRE) What's he talking about? A little vocabulary help from Wikipedia: > Consanguinity ("blood relation", from the Latin consanguinitas) is the property of being from the same kinship as another person. In that aspect, consanguinity is the quality of being descended from the same ancestor as another person

I ask because I'm trying to understand whether the prohibition against sibling marriage is due to genetic or emotional reasons. Suppose Bob and Alice marry, have a daughter Eve, and some years later Alice dies. Suppose Chris and Diana marry, have a son Frank, and some years later Chris dies. Now, suppose Bob and Diana marry -- that would make Eve and Frank stepsiblings with no shared biological heritage. Would the Old Testament law, in this case, prohibit Eve and Frank's marriage?

Did God allowed incest before? Did Noah and his family committed incest? If yes when did God start forbidding it and why? If no, how did Noah and his family repopulate the world and how about the risk of genetic diseases caused by the inbreeding?

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?