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If we restarted Earth with 120 people, how long until we get to 8 billion? (feddit.org)
submitted 3 weeks ago by to c/asklemmy@lemmy.world
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[–] 85 points 3 weeks ago (20 children)

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.

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  • [–] 16 points 3 weeks ago* (9 children)

    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

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  • [–] 7 points 3 weeks ago (6 children)

    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.

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  • [–] 7 points 3 weeks ago (4 children)

    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

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  • [–] 4 points 3 weeks ago

    Don't know about the DNA but White Sands Footprints were dated over 20,000 years old, someone arrived before land bridge was available.

    General rule in wildlife biology 50/500. Need 50 individuals to prevent extinction, 500 to have potential to evolve/survive threats.

    Here are a couple papers that say those numbers are too low but I don't have access to free copies. Second one a little beyond my understanding.

    https://www.sciencedirect.com/science/article/abs/pii/S0006320713004576?via=ihub

    https://www.sciencedirect.com/science/article/abs/pii/S0006320706002126?via=ihub

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  • [–] 3 points 3 weeks ago (2 children)

    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:

    https://en.wikipedia.org/wiki/Peopling_of_the_Americas

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  • [–] 4 points 3 weeks ago (1 child)

    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.

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  • [–] 5 points 3 weeks ago

    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.

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  • [–] 5 points 3 weeks ago (4 children)

    Even if we started with as genetically diverse set of 120 people as we could manage?

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  • [–] 9 points 3 weeks ago* (1 child)

    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.

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  • [–] 3 points 3 weeks ago*

    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.

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  • [–] 1 point 3 weeks ago*

    Although we're pretty damn adaptable already. If we go extinct, it won't be because we just can't handle a slightly different environment, like a bird or plant. We're tropical apes that have long thrived on fucking sea ice in houses made of snow.

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