# Minimum number of breeding pairs for humans to repopulate the world? **URL:** \ **Category:** Factual Questions\ **Created:** [December 22, 2016, 6:34pm UTC](https://boards.straightdope.com/t/minimum-number-of-breeding-pairs-for-humans-to-repopulate-the-world/775392 "2016-12-22T18:34:17Z")\ **Posts on this page:** 14\ **Page:** 4
**Author:** ![coremelt](https://avatars.discourse-cdn.com/v4/letter/c/4491bb/32.png) [@coremelt](https://boards.straightdope.com/u/coremelt)\ **Post date:** [December 25, 2016, 10:37am UTC](https://boards.straightdope.com/t/minimum-number-of-breeding-pairs-for-humans-to-repopulate-the-world/775392/61 "2016-12-25T10:37:36Z")
> [@dtilque](#): > > Nah, that’s the old standard plot. The new standard says the two men would turn out to be gay or perhaps trans. Or gay AND trans. Hilarity ensues. There’s probably a tvtrope about this, but I’m too lazy to hunt it down. Gay / trans wouldn’t be a problem. Plenty of Gay men have impregnated women to keep up appearances or due to family pressures. And if the flesh is weak then there’s always a Turkey baster. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [December 25, 2016, 12:54pm UTC](https://boards.straightdope.com/t/minimum-number-of-breeding-pairs-for-humans-to-repopulate-the-world/775392/62 "2016-12-25T12:54:20Z")
A transsexual man would almost certainly be biologically incapable of impregnating a female, and if you actually meant a transsexual woman, if she’s gone through surgery and/or hormonal treatment, she might have become biologically incapable of impregnating a female. ---
**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 25, 2016, 2:15pm UTC](https://boards.straightdope.com/t/minimum-number-of-breeding-pairs-for-humans-to-repopulate-the-world/775392/63 "2016-12-25T14:15:15Z")
We did have a poster once whose child was sired by her transwoman lover, leading to much derision after the phrase “woman sperm” was posted. As she was also (and I assume still is) married to a cisman (who happened to be sterile) the family dynamics were a bit complicated. Which, I hasten to add, was only a small portion of that person’s contribution to this forum. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [December 25, 2016, 4:33pm UTC](https://boards.straightdope.com/t/minimum-number-of-breeding-pairs-for-humans-to-repopulate-the-world/775392/64 "2016-12-25T16:33:45Z")
> [@Chronos](#): > > And given an answer of “one pair is enough, if you’re lucky”, it’s still worth asking “OK, how many do you need if you’re not lucky?”. Of course, there’s no single answer to that, because it depends on how much luck you consider acceptable, but the point is, there’s still room for further discussion. The OP basically asked whether problems with inbreeding would necessarily preclude a single pair of humans from repopulating the world. The answer to that is “no.” (As I mentioned, the present population of 250 of Black Robin of the Chatham Islands are all descended from a single fertile female. Their population size is mainly limited now by availability of suitable habitat. Otherwise they would be able to increase even more.) Obviously, however, the more individuals and more genetic diversity you have the better odds a population has for long term survival and increase. Even if there are detrimental recessives present in a population, that does not necessarily doom it. If they are lethal, however, they may reduce the rate of increase. Insular groups like Mennonite and Hasidic Jews have detrimental recessives, but these do not prevent these groups from having a high rate of increase. Other factors besides inbreeding can be a threat to very small populations, in particular chance deviations in sex ratio. If your founding pair had all boys then you’ll be out of luck, even in the absence of genetic problems. The OP only asked about inbreeding, but of course there are also extrinsic threats to the survival of very small populations, such as natural disasters, weather events, etc. For animals in their natural environment, a [Minimum Viable Population](https://en.wikipedia.org/wiki/Minimum_viable_population) can be calculated. This is usually calculated as the population size necessary to ensure between 90 and 95 percent probability of survival between 100 and 1,000 years into the future. Calculated MVPs are often in the range of 500-1000 when inbreeding is ignored, and several thousand when it is included. However, this says nothing about what the minimum possible founder population might be, just the population size you want to get up and maintain to to ensure long term survival. Also, it refers to populations of wild animals in the absence of human intervention. Humans would be better able to protect themselves from the impact of natural disasters. They would also potentially be able to consciously manage inbreeding problems (as human societies already do with prohibitions against incest). ---
**Author:** ![Atomic\_Alex](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/atomic_alex/32/175_2.png) [@Atomic\_Alex](https://boards.straightdope.com/u/Atomic_Alex)\ **Post date:** [December 25, 2016, 8:11pm UTC](https://boards.straightdope.com/t/minimum-number-of-breeding-pairs-for-humans-to-repopulate-the-world/775392/65 "2016-12-25T20:11:21Z")
> [@Colibri](#): > > The OP basically asked whether problems with inbreeding would necessarily preclude a single pair of humans from repopulating the world. The answer to that is “no.” I’m really surprised at that, thank you everyone for a fascinating thread, this is why I use the Straightdope. 🙂 ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [December 27, 2016, 6:34am UTC](https://boards.straightdope.com/t/minimum-number-of-breeding-pairs-for-humans-to-repopulate-the-world/775392/66 "2016-12-27T06:34:42Z")
We’re also glossing over another issue - reproduction ability. I know of one couple who tried hard and took 6 years to have 2 children, a few miscarriages, and an abortion when ultrasound showed twins with no brains developing. Another couple who had given up, until after almost 20 years of marriage she became pregnant (and only had one child). Another couple I know have never been able to conceive despite trying. (The wife joked “my aunt asked me about birth control, I laughed and told her I haven’t had to worry about it for the last 10 years”) So we are assuming our founding couple(s) can pump out kids one after another. Not every woman can do this. Like genetic problems - luck of the draw. ---
**Author:** ![Boyo\_Jim](https://avatars.discourse-cdn.com/v4/letter/b/87869e/32.png) [@Boyo\_Jim](https://boards.straightdope.com/u/Boyo_Jim)\ **Post date:** [December 27, 2016, 8:35pm UTC](https://boards.straightdope.com/t/minimum-number-of-breeding-pairs-for-humans-to-repopulate-the-world/775392/67 "2016-12-27T20:35:17Z")
> [@watchwolf49](#): > > [Victoria’s haemophilia](https://en.wikipedia.org/wiki/Haemophilia_in_European_royalty) is something of a case study of the problems with in-breeding … so the point is not every child will be fucked up … > > Someone did a study on field mice in central Ukraine … they found about a 3% birth defect rate … they did the same study on the field mice nesting _on_ the old sarcophagus at Chernobyl and found a 6% birth defect rate … certainly intolerable for humans … but the mice are thriving … I’m ready to try a survivor’s experiment with the Victoria’s Secret models, even if they all have Victoria’s Hemophilia. It’s just the kind of giver I am. ---
**Author:** ![Melbourne](https://avatars.discourse-cdn.com/v4/letter/m/b5e925/32.png) [@Melbourne](https://boards.straightdope.com/u/Melbourne)\ **Post date:** [December 27, 2016, 11:51pm UTC](https://boards.straightdope.com/t/minimum-number-of-breeding-pairs-for-humans-to-repopulate-the-world/775392/68 "2016-12-27T23:51:07Z")
> [@md2000](#): > > I suppose there’s a breeding _menage a trois_, and so on? menagerie a trois? The examples quoted above for population recovery are for intensively managed species. The point is that birds and animals aren’t programmed specifically for “species recovery”. If you have 2, they may just not like each other. One or both may be LGBTIQA+. Some may be too old for breeding. If they have distinct ranges, they may never meet. If the aliens manage species recovery, they may one male human in China, and a couple of young women in Aus. They may still have difficulty convincing their specimans to mate. If their aren’t any aliens, the man in China and the Australian women will never have children at all. Furthermore, without a functional society, they are all going to find it very difficult to get enough to eat: some of the early European/American settlers would have starved to death if not fed by the local population. If we take the hopefull postion that the breeding pairs are from an existing social group in a subsistance culture, like a couple of villages in PNG, then genetic diversity may be a problem. If you’re talking about NYC, then maybe they’d all be dead before that. ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [December 28, 2016, 12:37am UTC](https://boards.straightdope.com/t/minimum-number-of-breeding-pairs-for-humans-to-repopulate-the-world/775392/69 "2016-12-28T00:37:28Z")
> [@Melbourne](#): > > menagerie a trois? > > … If the transporter doesn’t work. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [December 28, 2016, 1:11am UTC](https://boards.straightdope.com/t/minimum-number-of-breeding-pairs-for-humans-to-repopulate-the-world/775392/70 "2016-12-28T01:11:20Z")
Eh, if the Last Couple on Earth are in NYC, they probably won’t have a hard time for food. The city’s grocery stores have about a week’s worth of food for 8 million inhabitants. Even if half of that is perishable, that’s still 80,000 people-years worth of food. ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [December 28, 2016, 1:47am UTC](https://boards.straightdope.com/t/minimum-number-of-breeding-pairs-for-humans-to-repopulate-the-world/775392/71 "2016-12-28T01:47:39Z")
> [@Chronos](#): > > Eh, if the Last Couple on Earth are in NYC, they probably won’t have a hard time for food. The city’s grocery stores have about a week’s worth of food for 8 million inhabitants. Even if half of that is perishable, that’s still 80,000 people-years worth of food. Given the half-life of a twinkie, they are probably safe for a few hundred years! 🙂 ---
**Author:** ![Steve\_MB](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/steve_mb/32/5339_2.png) [@Steve\_MB](https://boards.straightdope.com/u/Steve_MB)\ **Post date:** [December 28, 2016, 1:53am UTC](https://boards.straightdope.com/t/minimum-number-of-breeding-pairs-for-humans-to-repopulate-the-world/775392/72 "2016-12-28T01:53:39Z")
> [@md2000](#): > > Perhaps the best example to use would be the inhabitants of Easter Island. I don’t know how many they started with, but I assume it was one flotilla, so what - maybe 50 “breeding pairs”? Plus they would have been at the tail end of progressively more isolated populations on more and more remote islands. Before environmental collapse and/or European diseases came along, they were up to 15,000 and no indication of genetic issues. > > > [@](#): > > > > Early European visitors to Easter Island recorded the local oral traditions about the original settlers. In these traditions, Easter Islanders claimed that a chief Hotu Matu’a[3] arrived on the island in one or two large canoes with his wife and extended family.[4] They are believed to have been Polynesian. There is considerable uncertainty about the accuracy of this legend as well as the date of settlement. Published literature suggests the island was settled around 300–400 CE, or at about the time of the arrival of the earliest settlers in Hawaii. Some scientists say that Easter Island was not inhabited until 700–800 CE The best really long-term example I know of is Tasmania (several thousand people cut off for about 10,000 years). ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [December 28, 2016, 6:31am UTC](https://boards.straightdope.com/t/minimum-number-of-breeding-pairs-for-humans-to-repopulate-the-world/775392/73 "2016-12-28T06:31:12Z")
> [@Steve\_MB](#): > > The best really long-term example I know of is Tasmania (several thousand people cut off for about 10,000 years). True, but that’s the debate - isn’t it? Most likely Tasmania was at the carrying capacity of the land before it got cut off; all that population did was survive, maybe dwindle as the climate changed and the land area grew smaller? Whereas with Easter Island, a single flotilla, maybe 50 to 100 people, two canoes(?) created a population eventually guessed to be somewhere between 3,000 to 15,000 or more. The number responsible for populating the Americas initially may have been several thousand or less before rising waters separated America from Asia. The population before the European diseases arrived has been estimated to number tens of millions. But the point with either example is that a small population can continue, expand if resources allow, and rarely does it appear that less diverse genetics are a problem. Once the first few generations have ensured that there will be sufficient numbers to carry on, things seem to go well. ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [December 28, 2016, 3:20pm UTC](https://boards.straightdope.com/t/minimum-number-of-breeding-pairs-for-humans-to-repopulate-the-world/775392/74 "2016-12-28T15:20:32Z")
I suppose I should also mention Pitcairn Island, where… > [@](#): > > In 1790 nine of the mutineers from the Bounty, along with the native Tahitian men and women who were with them (six men, eleven women and a baby girl), settled on Pitcairn Islands and set fire to the Bounty. By the time the outside world came back and the sole Bounty survivor was an old man, there was a healthy population on the island. It should be noted though that an earlier settlement by Polynesians failed because the island(s) of the Pitcairn group did not have the resources to support a full Polynesian community. > [@](#): > > The population peaked at 233 in 1937 and has since fallen owing to emigration, primarily to New Zealand Of course, that included some other immigrants, especially missionaries. [Previous page](https://boards.straightdope.com/t/minimum-number-of-breeding-pairs-for-humans-to-repopulate-the-world/775392.md?page=3)