# How many generations needed until breeding between descendants doesn't matter? **URL:** \ **Category:** Factual Questions\ **Created:** [June 15, 2025, 3:59pm UTC](https://boards.straightdope.com/t/how-many-generations-needed-until-breeding-between-descendants-doesnt-matter/1019658 "2025-06-15T15:59:50Z")\ **Posts on this page:** 10\ **Page:** 3
**Author:** ![Gordon\_G](https://avatars.discourse-cdn.com/v4/letter/g/3da27b/32.png) [@Gordon\_G](https://boards.straightdope.com/u/Gordon_G)\ **Post date:** [June 19, 2025, 4:02am UTC](https://boards.straightdope.com/t/how-many-generations-needed-until-breeding-between-descendants-doesnt-matter/1019658/41 "2025-06-19T04:02:35Z")
> [@Northern\_Piper](#): > > Political reasons in England and thus Commonwealth countries being that Henry VIII wanted to marry his deceased wife’s cousin five centuries ago. Who was that? Anyway, _that_ type of incest does not lead to inbreeding. Prohibition against marrying a sister-in-law may have been to reduce the incentive for jealousy-caused fratricide. Both Queen Mary I and Queen Elizabeth I could be considered “bastards” since Mary’s mother had earlier been the wife of Henry VIII’s brother Arthur, and Elizabeth’s mother was the sister of Henry’s earlier mistress, Mary Boleyn. ---
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [June 19, 2025, 5:01am UTC](https://boards.straightdope.com/t/how-many-generations-needed-until-breeding-between-descendants-doesnt-matter/1019658/42 "2025-06-19T05:01:01Z")
> [@Gordon\_G](#): > > Who was that? See post 16, above: > [@Northern\_Piper](#): > > Blame Henry VIII ! ---
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [June 19, 2025, 5:03am UTC](https://boards.straightdope.com/t/how-many-generations-needed-until-breeding-between-descendants-doesnt-matter/1019658/43 "2025-06-19T05:03:49Z")
> [@Chronos](#): > > > [@Northern\_Piper](#): > > > > Political reasons in England and thus Commonwealth countries being that Henry VIII wanted to marry his deceased wife’s cousin five centuries ago. > > Surely, the simpler solution would have been to amend the inbreeding laws to apply only to blood relatives. That’s assuming that the bar was based on modern knowledge. Instead, it was an ecclesiastical rule, based on the church’s interpretation of biblical teachings, possibly including social stability principles, as @Gordon_G suggests. Henry got rid of it as part of his reformation / break from Rome / horniness, not based on scientific reasons. ---
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [July 10, 2025, 2:30am UTC](https://boards.straightdope.com/t/how-many-generations-needed-until-breeding-between-descendants-doesnt-matter/1019658/44 "2025-07-10T02:30:38Z")
I was browsing Wikipedia and came across this tidbit: > The U.S. is the only western country with cousin marriage restrictions, no European country prohibits marriage between first cousins.[[58]](https://en.m.wikipedia.org/wiki/Marriage_law#cite_note-64) The cite goes to a NYT article that says there is no genetic reason to discourage first cousin marriage. ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [July 10, 2025, 3:03am UTC](https://boards.straightdope.com/t/how-many-generations-needed-until-breeding-between-descendants-doesnt-matter/1019658/45 "2025-07-10T03:03:58Z")
> [@Northern\_Piper](#): > > The cite goes to a NYT article that says there is no genetic reason to discourage first cousin marriage. True. But if cousins marry cousins who marry cousins and so on, things could and did get bad. But they are right- _today,_ there are no reasons to forbid cousin marriage. We are past the Habsburgs now. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [July 10, 2025, 4:21pm UTC](https://boards.straightdope.com/t/how-many-generations-needed-until-breeding-between-descendants-doesnt-matter/1019658/46 "2025-07-10T16:21:21Z")
And _mostly_ past the “isolated village in some Appalachian holler” stage. Besides, for that crew the damage is already mostly done. ---
**Author:** ![Broomstick](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/broomstick/32/246_2.png) [@Broomstick](https://boards.straightdope.com/u/Broomstick)\ **Post date:** [July 10, 2025, 4:26pm UTC](https://boards.straightdope.com/t/how-many-generations-needed-until-breeding-between-descendants-doesnt-matter/1019658/47 "2025-07-10T16:26:20Z")
Hey! My in-laws represent that remark! (Seriously, they do. In every way) ---
**Author:** ![Melbourne](https://avatars.discourse-cdn.com/v4/letter/m/b5e925/32.png) [@Melbourne](https://boards.straightdope.com/u/Melbourne)\ **Post date:** [July 11, 2025, 12:23pm UTC](https://boards.straightdope.com/t/how-many-generations-needed-until-breeding-between-descendants-doesnt-matter/1019658/48 "2025-07-11T12:23:48Z")
> [@Chronos](#): > > Well, by the simple (continuous) models, the rate of the recessive gene would asymptotically approach 0 There is/was an Australian family with a genetic flaw that only becomes evident at 30+, associated with disinhibition (like acquired brain injury or several “happy” syndromes and diseases) and early death like tertiary syphilis. Dunno what the status is now. They kept on having children in the “disinhibited” phase, and early death did not eliminate the genetic flaw. ---
**Author:** ![Loach](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/loach/32/350_2.png) [@Loach](https://boards.straightdope.com/u/Loach)\ **Post date:** [July 11, 2025, 1:12pm UTC](https://boards.straightdope.com/t/how-many-generations-needed-until-breeding-between-descendants-doesnt-matter/1019658/49 "2025-07-11T13:12:16Z")
> [@Northern\_Piper](#): > > I was browsing Wikipedia and came across this tidbit: > > > The U.S. is the only western country with cousin marriage restrictions, no European country prohibits marriage between first cousins.[[58]](https://en.m.wikipedia.org/wiki/Marriage_law#cite_note-64) > > The cite goes to a NYT article that says there is no genetic reason to discourage first cousin marriage. But it certainly isn’t universal here either. 26 out of 50 states allow 1st cousin marriage either completely or with some restrictions. Most Americans wouldn’t guess that’s the answer. In two states incest between adults is legal regardless of how closely related. They just can’t get married. You wouldn’t guess the states if you are going by the stereotypes. It’s New Jersey and Rhode Island. ---
**Author:** ![bob\_2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bob_2/32/3341_2.png) [@bob\_2](https://boards.straightdope.com/u/bob_2)\ **Post date:** [July 11, 2025, 1:48pm UTC](https://boards.straightdope.com/t/how-many-generations-needed-until-breeding-between-descendants-doesnt-matter/1019658/50 "2025-07-11T13:48:04Z")
1st cousin marriages only become a serious problem when they are repeated. This has happened when some people prefer to arrange marriages within their family group. The Bill in the UK Parliament was introduced using the 10-minute rule process, which allows a backbench MP to make the case for a new bill in a speech of up to 10 minutes in the Commons. However, such bills are unlikely to become law without government support because of the limited parliamentary time available for them, and the government has made it clear that it won’t. [Previous page](https://boards.straightdope.com/t/how-many-generations-needed-until-breeding-between-descendants-doesnt-matter/1019658.md?page=2)