47
Depends which 120
Well: if we believe Christianity we only needed 6k-10k years from two people to the billions we have today, so it shouldn’t take so long
The current consensus is that the minimum viable population for most species is between 500 to 1,000 individuals.
The problem isn’t inbreeding depression (you only need about 50 individuals to avoid that)—it’s lack of diversity to adapt to a changing environment. Pathogens would evolve that would wipe out the entire species because they’re too genetically homogeneous.
I saw an episode of Nova years ago where dna analysis showed as few as 70 people crossed the Bering land bridge and formed the basis of all Native Americans.
https://www.livescience.com/289-north-america-settled-70-people-study-concludes.html
Now they're pretty sure that people used boats and skirted the coastline but didn't walk.
This is a great video about human migration to the Americas https://youtu.be/UsnrdCdGs7o
That article's over 20 years old—I'm not up on the latest findings, but I know there's been major work since then on both the peopling of the Americas and on the importance of genetic diversity.
Along with other bottlenecks once thought to be humans on the brink of extinction, like with the Toba eruption, further research tends to find other evidence to reverse the extreme nature speculated on. We do on the other hand have evidence of other species that had bottlenecks caused from disasters and the genetic signs are very obvious. Cheetahs as an example.
It's the other way around. It was once believed that a population of hundreds were needed but the DNA evidence proved it to be much smaller. If you have newer information that shows the DNA work done was wrong, please post it because I've been pulling out this trivia for years.
https://en.wikipedia.org/wiki/Genetic_history_of_the_Indigenous_peoples_of_the_Americas
Hmm... the only cited sources in that article for a specific (effective) population size are also over 20 years old—the more recent sources just say it was likely a “small” number.
This article has a lot more detail on the various migration theories, but refrains from any specific size estimates:
the only cited sources in that article for a specific (effective) population size are also over 20 years
When research is old without being found wrong, it is more likely to be correct.
Yup. 500 is a better number as a minimum, but 120 is to small.
https://scicentric.org/minimum-viable-population-humans
Also this kind of happened already
https://www.thecollector.com/mount-toba-supervolcano-wipe-out-humans/
I think that number is just for a guaranteed successful outcome. Aboriginal people migrated to Australia with maybe as few as a few dozen
Even if we started with as genetically diverse set of 120 people as we could manage?
I can’t remember where I read this, but if carefully managed, humanity, in a highly controlled environment, could start off with as little as around 36 individuals. But population and reproduction would have to be highly controlled for dozens of generations before we could breed freely. this is all purely from a genetic standpoint.
And, of course, we would have to be in an environment where we wouldn’t worry about food or pathogens or predators, or anything else that might be a threat to our survival— including each other, or, possibly, ourselves.
The comment you were responding to is estimating a necessary population that takes into account a lot of other environmental factors.
All Native Americans were decended from a population of 70 that crossed the Bering land bridge.
https://www.livescience.com/289-north-america-settled-70-people-study-concludes.html
You're going to need more diversity than just genetic. With that few people, you're going to need doctors, mechanics, scientists, farmers, people with knowledge that can help the colony prosper and prevent what we thinknof as easily prevented diseases and injuries and illnesses.
For example, there's a pretty good percentage of potentially fatal issues during childbirth. Just a few of those and you're greatly impacting your genetic diversity. Immunizations and medicine needs all sorts of production facilities and raw materials, so it's not just "maybe a doc can help me not die giving birth or at least let me try again." Sure, we're animals that can handle some of that naturally, but with that slim of a margin, it's going to be impactful.
If you cherry picked you'd likely be fine.
Ok but humans are the literal most adaptable species ever
Humanity started growing massively when the Industrial Revolution hit:
Source: https://ourworldindata.org/population-growth-over-time
So, that would be a factor, whether they'd still have access to technology (and whether we'd expect them to be able to maintain at least some of this technology).
From the aspect of starting over with the existing world, we've depleted most of the much easier resources we had to work with the first time around, so the second climb up technology's ladder would be far harder, maybe even impossible. Reuse and salvage is one route we would take, but some materials can't be. Either they can't be recycled or reclaimed, or like some alloys we've made can't be just melted down and reused, some even can't be reshaped. So many things require an existing and running infrastructure to just make these things.
The first episode of James Burke's Connections series touches on this. Things we don't even think about that support civilization because we've built up around them for centuries, and a lot of it in the most recent century. Starting from base level is far more difficult than the first time around... and like I said, before we had much different resources around us to support the growth.
From a population of about 1300 individuals, it took 900,000 years to grow to todays 8 billion, theoretically.
You never would. You picked all males.
7000 years.
But 120 people means: zero division of labor, zero technology, only stone age and all are generalists.
Can you explain how you get to that number? Assuming how many surviving kids and how long til they reproduce again?
I don’t know that 120 people offers enough genetic diversity for a species to thrive. The population would, the way I see it, increase for a while and then start to collapse.
Depending on the 120 people. Most of these people are still in the primitive ages with tech and science so they will talk about genetics not knowing shit.
It would give a serial killer a real shot at ending the cycle
Like malaria
I think she spells it “Melania.”
Assuming the 120 people have access to existing world history I'd hope they manage to arrange things such that they never get into that kind of trouble.
We won't.
Way too inbred
Do they all start in the same area? Or are they spread out across the globe?
this post was submitted on 22 Aug 2026
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