Just having an argument with a friend
In: 4
Yes! If the two were women, fertility specialist, and had a large gene bank at their disposal.
Two is obviously under a minimal viable population for humans, but humans are clever and adaptable, and if there’s two of them left they could use the stored genetic material of the other humans (whom let’s assume have all gone to a very nice planet where they can run and play), to create embryos unrelated to our 2 women population.
These two determined women could produce and raise 20 people. If they select only female embryos for implantation and repeat the process with their daughters, teaching them to keep up the family business, your third generation would be 200 people with minimal genetic ancestors in common. At this point you could stop relying on a gene bank and female-only embryo selection (a good thing too, as even with short generations you’d be running out of viable genetic material in the freezers) and go back to making new humans the old fashioned way.
You’d want to keep careful track of parentage and ancestry to minimize inbreeding, but 200 is a viable population.
Edit: Basic math fix.
For a while, but it would eventually either no longer be human or be incapable of surviving and/or breeding.
Every animal has a certain amount of genetic complexity, which contributes to the minimum population needed to make infinite population growth. Some species can actually clone themselves as their main means of reproduction, so that minimum population is One.
Humans are not that. I dont know how true it is, but the magic number I heard was 10,000. Any less than that and the lack of genetic diversity would eventually burn out the species.
Everyone is all wrapped up about the genetics involved, but the reality is that without modern medical support the chances that the female will die during labor or shortly thereafter from infection are startlingly high. What happens if mom cranks out two boys and then dies from a hemorrhage? Goodbye humanity.
Functionally, no. Within a very few generations, the inbreeding problems would be rampant to the point of non-sustainability, especially without things like skilled doctors.
Yes!
Would at end well?
No!
Assuming two random people? I suspect they’d be lucky to survive the first childbirth
Genetic issues aside. Has anyone done math? Assume 1+1 = 4, and they tell two friends, and they tell two friends. How many people would it be over the current average lifespan?
That depends on what counts as a person, and on which two people. Here’s the best case scenario I can come up with off the top of my head:
* both people are healthy cis women
* both are interested in bearing large numbers of children, and are young enough that they could
* they know each other, and know that they’re the last two people on Earth
* they manage to preserve a large number of genetically diverse frozen embryos at an IVF lab before lack of human oversight causes the power grid and freezing equipment to fail
* I don’t count frozen embryos as people. Maybe you do. This is a subject where reasonable people can disagree.
* they survive the collapse of all the infrastructure
* they manage to work the equipment that defrosts and implants a frozen embryo into a person, and use it many times on each other
* luck is on their side, so no chance illnesses strike either during any of their numerous pregnancies
* all the children survive
* the initial survivors teach the children how to operate all the equipment preserving and using frozen embryos
* enough of the children are interested in repopulating the Earth with healthy humans to get the species over the [Minimum Viable Population](https://en.wikipedia.org/wiki/Minimum_viable_population)
It seems plausible that it could work, though I sure wouldn’t wanna bet on it.
The only way they could repopulate the earth is if they had perfect genetics. Which, of course, none of us do. Otherwise within 4 generations (if they’re lucky!) the babies being born would have such a tangled mess of recessive genes and birth defects that there wouldn’t likely be a 5th.
Lots of people are talking about the lack of genetic diversity, but I think the more critical factor here is that the world is _dangerous_. Two people on their own without anyone else to help them are going to have a hard time just staying alive. Something as simple as eating the wrong berry, or drinking from the wrong stream, or getting a little cut and having it get infected could kill them. On top of that, pregnancy and childbirth are incredibly dangerous to the mother and the baby, and without knowledgeable people to help out, the odds are very small that she would survive enough pregnancies to produce enough children who could themselves survive long enough to reproduce.
So, the odds are stacked against them just in terms of survival, but if they did manage to do that then the odds that they could reproduce more than a couple of times are very low, and if they could do that then the odds that _those_ kids would survive is very low.
I don’t think there would be enough generations for inbreeding to even show up as a problem, but if they got super lucky for a several decades, then they’d have to deal with that as well.
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