# How much "genetic distance" is needed for inbreeding to not be a problem? **URL:** \ **Category:** Factual Questions\ **Created:** [December 6, 2018, 9:32am UTC](https://boards.straightdope.com/t/how-much-genetic-distance-is-needed-for-inbreeding-to-not-be-a-problem/825663 "2018-12-06T09:32:54Z")\ **Posts on this page:** 9\ **Page:** 3
**Author:** ![eschereal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eschereal/32/18939_2.png) [@eschereal](https://boards.straightdope.com/u/eschereal)\ **Post date:** [December 8, 2018, 9:09pm UTC](https://boards.straightdope.com/t/how-much-genetic-distance-is-needed-for-inbreeding-to-not-be-a-problem/825663/41 "2018-12-08T21:09:00Z")
Are the lower limits for source population based on exclusivity (monogamy)? Because it seems like a promiscuous group is going to be viable for a much smaller population. ---
**Author:** ![Hector\_St\_Clare](https://avatars.discourse-cdn.com/v4/letter/h/b5ac83/32.png) [@Hector\_St\_Clare](https://boards.straightdope.com/u/Hector_St_Clare)\ **Post date:** [December 9, 2018, 7:11am UTC](https://boards.straightdope.com/t/how-much-genetic-distance-is-needed-for-inbreeding-to-not-be-a-problem/825663/42 "2018-12-09T07:11:56Z")
> [@rat\_avatar](#): > > To add to this, while the single migration model is in question in the Americas, the estimated effective size of the groups that peopled the New World is only around 70 individuals. Correct me if I’m wrong, but there wasn’t just one “group” that peopled the new world. Navajos and other Na-Dene speakers etc. derived from a separate and much later migration event, right? ---
**Author:** ![filmstar-en](https://avatars.discourse-cdn.com/v4/letter/f/50afbb/32.png) [@filmstar-en](https://boards.straightdope.com/u/filmstar-en)\ **Post date:** [December 10, 2018, 9:36am UTC](https://boards.straightdope.com/t/how-much-genetic-distance-is-needed-for-inbreeding-to-not-be-a-problem/825663/43 "2018-12-10T09:36:58Z")
Here is a BBC documentary about cousin marriage amongst the Pakistani community in the UK and the health problems it causes. ‘should I marry my cousin’ [Should I Marry My Cousin (BBC / 2017) on Vimeo](https://vimeo.com/223139325) Cousin marriage is also tradition amongst Aristocracies in order to preserve a royal lineage in the days when being a member of a royal family, put on this earth to rule by divine ordinance was an important political advantage when it came to deciding who would be King. > **[Pedigree Chums: A History of Aristocratic Incest | The Rake](https://therake.com/stories/code/pedigree-chums-a-history-of-aristocratic-incest/)** > > Incest is one of the last great taboos, yet it has remained rife within the Western world’s most illustrious – particularly royal – clans. Stuart Husband looks on, treading water, from… The same idea was adopted by some of the American corporate dynasties like the DuPonts and the Rothchilds. I guess how safe it is depends very much on what nasty recessive gene lie lurking in the family genome. The answer to that question is nearly solved as the cost of genome sequencing becomes cheaper and we learn how to assess the risk of congenital disease between two individuals accurately. Combine that with gene editing and IVR and the future presents some interesting ethical issues. Some of these issues were explored in the SciFi movie Gattaca. > **[Gattaca](https://en.wikipedia.org/wiki/Gattaca)** > > Gattaca is a 1997 American dystopian science fiction thriller film written and directed by Andrew Niccol in his directorial debut. It stars Ethan Hawke and Uma Thurman with Jude Law, Loren Dean, Ernest Borgnine, Gore Vidal, and Alan Arkin appearing in supporting roles. The film presents a biopunk vision of a future society driven by eugenics where potential children are conceived through genetic selection to ensure they possess the best hereditary traits of their parents. The film centers o The f... ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [December 10, 2018, 7:44pm UTC](https://boards.straightdope.com/t/how-much-genetic-distance-is-needed-for-inbreeding-to-not-be-a-problem/825663/44 "2018-12-10T19:44:28Z")
Re Pakistani intermarriage - From what I heard on a few documentaries a while ago, cousin (well, 2nd and third especially) is what builds the clans in some middle eastern communities. There are several groups, call them clans, or extended families or tribes or whatever (all loaded words). basically, the clans are extended families which reinforce the bonds with marriages to others of the same extraction, who tend to be moderately closely related. Thus you have many comingled but not usually related groups or families in the same general area. it was suggested too that part of the Palestinian problem was not so much political or ideological, as inter-tribal conflict for dominance between different clans, some of whom support one faction or the other; hence the fight between Wes Bank and Gaza. Until they can agree to put old rivalries aside and work together, the region will be to fractured to agree among each other, let alone talk peace with an outside group. ---
**Author:** ![Treppenwitz](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/treppenwitz/32/3445_2.png) [@Treppenwitz](https://boards.straightdope.com/u/Treppenwitz)\ **Post date:** [December 14, 2018, 10:14am UTC](https://boards.straightdope.com/t/how-much-genetic-distance-is-needed-for-inbreeding-to-not-be-a-problem/825663/45 "2018-12-14T10:14:06Z")
FWIW - More on UK Pakistani cousin marriage, published on BBC today. > **[Did my children die because I married my cousin?](https://www.bbc.co.uk/news/stories-46558932)** > > Ruba and Saqib both carry a gene for I-cell disorder, which means their children have a one-in-four chance of dying in early childhood. The only bright spot: \*The couple’s experiences have led others in the family, including Ruba’s brother, to reject cousin marriage. “We never use to think about the risks - up to my children we’ve never thought it was wrong to marry in the family, but because I’ve been through it my other relatives do think twice about going in the family,” Ruba says.\* The rest is just distressing. j ---
**Author:** ![Ann\_Hedonia](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ann_hedonia/32/319_2.png) [@Ann\_Hedonia](https://boards.straightdope.com/u/Ann_Hedonia)\ **Post date:** [December 14, 2018, 2:26pm UTC](https://boards.straightdope.com/t/how-much-genetic-distance-is-needed-for-inbreeding-to-not-be-a-problem/825663/46 "2018-12-14T14:26:53Z")
Another case in point. The polygamous FLDS community in Arizona has an unusually high incidence of a very rare recessive genetic disorder called fumerase deficiency. It’s a very rare condition (only a few dozen known cases). Over half of the known cases in the world are among residents of this tightly knit and isolated community. > **[The polygamous town facing genetic disaster](https://www.bbc.com/future/article/20170726-the-polygamous-town-facing-genetic-disaster)** > > In a remote region of the US, a town is struggling with a chilling health crisis caused by a recessive gene. The reason? Here, polygamy is still practised. ---
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [December 14, 2018, 6:57pm UTC](https://boards.straightdope.com/t/how-much-genetic-distance-is-needed-for-inbreeding-to-not-be-a-problem/825663/47 "2018-12-14T18:57:37Z")
> [@Ann\_Hedonia](#): > > Another case in point. > > The polygamous FLDS community in Arizona has an unusually high incidence of a very rare recessive genetic disorder called fumerase deficiency. It’s a very rare condition (only a few dozen known cases). Over half of the known cases in the world are among residents of this tightly knit and isolated community. > > [The polygamous town facing genetic disaster](http://www.bbc.com/future/story/20170726-the-polygamous-town-facing-genetic-disaster) Probably not the best example for the general case as polygamy reduces genetic diversity more than in a group with world-views that lead to a more horizontal parentage. One man having 55 wives and 59 children going to be a much larger choke point. ---
**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:** [December 14, 2018, 11:18pm UTC](https://boards.straightdope.com/t/how-much-genetic-distance-is-needed-for-inbreeding-to-not-be-a-problem/825663/48 "2018-12-14T23:18:27Z")
Specifically, that’s the Colorado City/Hilldale FLDS group which is one of the most inbred and cultish. Other FLDS polygamists are not nearly so genetically isolated. ---
**Author:** ![Guinastasia](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/guinastasia/32/5751_2.png) [@Guinastasia](https://boards.straightdope.com/u/Guinastasia)\ **Post date:** [December 15, 2018, 12:08am UTC](https://boards.straightdope.com/t/how-much-genetic-distance-is-needed-for-inbreeding-to-not-be-a-problem/825663/49 "2018-12-15T00:08:55Z")
> [@clairobscur](#): > > I suspect that in a lot of societies, most marriages involved people who were 3rd cousins or related more closely. I was raised in a rural area. When people were talking of someone, the conversation would almost always devolve in determining who is person was related to (“Wasn’t his aunt X, who was your husband’s cousin?”) and a family link was found pretty much all the time. I’m pretty sure I was third cousin of or more closely related to most of the local population. And the local people definitely married each other. > > And there are societies, even nowodays, where first cousin marriages are commonplace. I imagine that 3rd cousin marriages there must be repeated pretty often. > > Is there really a dangerously high level of birth defects related to inbreeding in these societies? Another good example would be the [Spanish Habsburgs](http://blogs.discovermagazine.com/gnxp/2009/04/inbreeding-the-downfall-of-the-spanish-hapsburgs/#.XBRFfs17mUk). [Previous page](https://boards.straightdope.com/t/how-much-genetic-distance-is-needed-for-inbreeding-to-not-be-a-problem/825663.md?page=2)