So, I assume that if you put 100 people on a spaceship and sent them to wherever, they’d get very inbred in a few generations. How many people would you need for this to not happen, accounting for the fact that there will eventually be people who are infertile or die before having children?
There are different answers depending on the end goal.
Mere survival: Isolated human populations have been bottlenecked to as few as a few hundred individuals and survived, IIRC.
A quick search says biologists like to see 25+ breeding pairs to maintain an animal species (if I’m reading that correctly). So 50-100 seems like pretty close to the minimum.
Long-term colony building with full genetic diversity needs a lot more: At least one estimate is as high as 40,000 people. The high number is for Earth-like diversity in the population, and with no need for any overarching breeding program, so it’s really kind of an outlier scenario. That 40k figure can be pared down significantly if you have strict protocols, or accept some loss of diversity.
So anywhere from 50 people to 40,000 people, but the end result will look wildly different at the extremes.
On a scale from Hapsburg to Earth, how do you want your new colony to go?
I like your answer because I feel the only real answer you can have is “more is better, less is worse”
How many should you take for good diversity? All 8 billion, more if you can find them.
It seems very plausible that if you can make a generation ship, you could make something like CRISPR to artificially increase genetic diversity/eliminate potential birth defects. Or perhaps just store genetic material for more people than the actual colonists on the ship. You’d probably want to hedge your bets in case there’s a low survival rate. There’s a lot that could go wrong. Ecosystem failure, negative effects of radiation, or just good old fashioned murder.
Pro tip: take frozen sperm/eggs with the ship. Can be used to infuse the population with fresh genetic material.
Nah, you’d ideally want 150-200, but 100 (20something and younger) would be fine assuming a random sample from all over.
The danger is the reinforcement of negative recessive genes. So if you just grab 100 from one area, there may already be common dangerous recessives that would become an issue in a few generations.
But grab a random sample of the billions of humans worldwide, you’d have the same number of “dangerous” recessives, just different ones. That would take a long time to spread within the new population.
It’s not like similar DNA is bad, it’s just compounding of recessive genes when there’s no natural selection. Which is why all the big examples of inbreeding is medieval royalty. They didn’t need to be physically/mentally capable of surviving, because they had inherited wealth.
Even better if the sample is not random, but at least screened for some genetic issues.
In the Galaxy’s Edge series this is tangentially addressed, the TLDR is that there are other implications of being on a ship for generations that outweigh the genetic problems. The Savages have a well earned title fwiw both in origin and action. It is a bleak outlook on the concept but I don’t think it is farfetched given everything we are living through right now.
There are actually two issues:
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The most obvious effect of inbreeding is the increase in homozygosity for deleterious mutations, causing more birth defects.
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A subtler effect is the loss of genetic diversity reducing a population’s ability to continue to evolve in response to future selection pressures. This would be especially important when migrating to a new environment with new selection pressures the species has never encountered before.
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