Just having an argument with a friend
In: 4
Yes, but not without…… issues. The resulting population would not be *healthy* by any means.
The way genes work, there are a lot of genes people have that are *recessive*, meaning they only become active in the individual if you inherit the same gene from both parents. Many recessive genes are *bad for you* to have active, but rare, because both your parents have to be carriers for it, but most people probably have at least a few weird recessive genes with negative effects on your health.
So if your population is all descended from 2 people, that means every individual is a semi-random selection of those 2 peoples’ genes, and after the 1st generation, their direct children, without new genes entering the gene pool, they have to populate the earth by sleeping with their siblings, or parents, but that certainly doesn’t make the problem any *better*.
And with that incest, your likelihood of 2 parents with the same, damaging recessive gene starts skyrocketing, considering they both inherited it from the same person, so your efforts to reformulated the earth will quickly have more health problems than the combined Nobility of Europe, and
Would be extremely vulnerable to disease, since our immune systems are heavily influenced by genetics as well. If one person in this community catches a disease that kills them, chances are *high* that litterally nobody will fare any better against it.
Look at animals. The minimum for starting a herd is 3, 2 females and a male. If they are all from separate sources, you can go many generations by breeding to whomever they are least related to. Long term, you need to incorporate more blood. For ethical reasons, I do not support breeding humans this way. Like, no one wants to bone their grandfather.
Yes.
People point out recessive issues popping up due to inbreeding, which is definitely a factor. But this is really only an issue when a few handful of each generation survive, increasing the chance that every member of the generation inherits the same gene. If a single couple (generation 0) produce 4 children, then generation 1 would have no issues and 25% of generation 2 would have issues, that’s 2 of the 8 members for that generation. A dozen generations later, there absolutely would be some problems popping up and the population would be overall less healthy than the current one, but at that point you’re looking at >1000 people.
If the question was phrased “could a 1000 people repopulate the earth” the answer would be a resounding yes.
Maybe ? Maybe, that’s why we’re here? Like in the timeline, not why we exist or whatever. Like maybe, because of inbreeding that’s why we are socially stupid but can technologically advance?I know I can only handle my cousins for so long before I have to have a drink.
Mathematically. No.
The most obvious argument would in fact be mathematical. If two people have kids, and those two people have kids, and those two people have kids. Yeah. No.
But, the question does need a bit more qualification. Is the scenario they are the last two people on earth? Or that all the other existing people have to stop having kids? If “last two people on earth” scenario, 100% no. So many variables. Who’d deliver the kids. Who’d provide health care. Even throwing all that out… who provides food, water, utilities. And even throwing all THAT out. You’d have to have 10-15 generations of people grow up, have kids, rinse and repeat and live relatively full and healthy lives. IF they do that, throwing out ALL that other stuff… maybe a small chance. Ice that cake with inbreeding causing some real bad genetic issues.
Everyone else on earth stop breeding? A higher chance, but still low. Same reasons as above, ultimately.
50/500 rule
You need a population of 50 unrelated individuals at the minimum, with controlled breeding to build a stable population of humans. And 500 to prevent genetic drift.
Not likely.
Take it like this: The entire Spanish branch of the Habsburg royal family became infertile over the span of 200 years due to inbreeding (1500-1700).
Their children had a 50% mortality rate, which was high even for the time.
By the reign of Charles II (The last of his bloodline), the physical deformities suffered were so bad he had to be raised like a baby until the age of 10, and even then, his mouth and throat were so distorted that he had trouble talking.
Best part about this? Only about 80% of their family marriages were consanguineous. They had a few new additions to the genepool. Your example of 2 people repopulating the earth would have a 100% rate.
**TLDR:** It is almost a certainty that the family would eventually die out before they got anywhere close to repopulating a single country, let alone the entire world.
For a better idea of how biologists grapple with the question, they use a guideline called the “50/500 rule”. It takes a minimum of ~50 individuals to combat the negative health effects of inbreeding. ~500 individuals are ideal to combat harsh shifts in the genepool. These numbers are flimsy, but 50 >>>>>>>>>> 2
Technically yes. Whatever birth defects they have typically wouldn’t cause enough problems to prevent reproduction.
Gross as it is, each generation would need to have at least 4 kids, but 8 kids probably works best to speed up the genetic diversity game. Birth defects don’t start to show until a few generations in. You’ll probably get some problems a couple generations in but it’s probably a jump that can be overcome.
Gen 0 are the two, let’s say they have 8 kids
Gen 1 are all siblings, they pair off. 4 branches. 8 kids each. Siblings are off limits now and we can start to create artificial diversity.
Gen 2 are all cousins. 32 kids means 16 pairs. 8 kids each. Cousins off limits now.
Gen 3, all second cousins.
Gen 4, all third cousins. Things are looking good. This is the point when things are technically “legal”. But that typically assumes you’ve had a couple generations of non-family DNA in the mix. Idk what happens if it’s all from the same ancestor, but at the very least, we can further the gap by 1 with each generation.
The REAL problem is the overlap. We can get rid of it be saying, siblings of one immediate family can only reproduce with siblings of another immediate family until the 4th generation. At that point the gene pool should hopefully be isolated enough that overlapping is more a help than hindrance.
Uneducated Opinion Here: I’d say that it’s possible, but the odds are gonna be extra stacked against them.
-How prepared are they – food, shelter, water
-Inbreeding issues
-Death of one of the two before conception of two opposite sexes-accidental, carnivores
-One being infertile/sterile
-Low population = greater risk of being wiped out by catastrophes-flood, earthquake, landslide, tornado, hurricane, volcanic eruption, disease, famine
Can it be done? Sure. It’s possible, but not likely.
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