How many humans would it take to save the species?

In a hypothetical situation where, for some reason, the earth becomes unsuitable for inhabitance, what is the minimum number of humans that should be contained in some sort of ‘ark’ to ensure survival of the human race?

Of course, this is accepting they have enough food, water, oxygen. I realise that numbers may change depending on how long they have to stay in the ‘ark’, so for some starting point lets say, 2 years, 5 years and 10 years. After this time whatever crisis it was is over and they can live survive on earth as before, but they are the only ones left. To make it easier, lets forget the animals and plants for a second.

I have no idea where to begin with this. I guess that it must be enough people to not screw up the gene pool. If the time were a lot longer than 10 years I assume the community would start growing and all sorts of crazy new needs would have to be accounted for. Guesses from my family have ranged from 2000 to 15,000 people, so any help would be appreciated.

  1. Barring an abundance of bad recessive genes.

Yes, the implications are gross, I know.

Other species have come back from the single digits. They’ve gone through a severely limiting genetic funnel, but they’re still around. I can’t for the life of me recall any species at the moment though. some bear… somewhere…

I’m no population biologist, but I think you’re guesses are a bit high. I’ve read several times that a few dozen people (30 or so) would provide enough genetic diversity to mitigate the problems associated with inbreeding.

Empirically speaking:

" The Bounty left Tahiti for its Pitcairn Island quest in 1789. Accompanying the nine mutineers were 6 Polynesian men and 12 Polynesian women. Each of the Englishmen had a wife or female companion. It is uncertain which of the natives joined the Englishmen by choice. "

Of course, it immediately descended into a lot of murder and suicide in the first few years:

"The natives resented this unfair treatment, which caused relationships between the Englishmen and the Polynesians to deteriorate. The hostility increased when Jack William’s wife died, and one of the Polynesians’ consorts was “given” to Williams as a “replacement”. Despite Fletcher Christian’s efforts to maintain peace, the Polynesian men revolted against their English oppressors in 1794. Several mutineers were killed, among them Fletcher Christian. The revolt of the natives enraged the widows of the dead mutineers. To avenge their husbands’ deaths, the Tahitian women killed the remaining Polynesian men. "

Sixty-one years later:

“By 1855, the population had grown to nearly 200, and the tiny island, with only 88 acres of flat land, could no longer sustain its people.”


The human species could survive passing through a VERY narrow bottleneck- even the “2” suggested earlier. More important would be how soon and how much the population could reexpand later. Studies of isolated Pacific islander populations suggest that in the long term you need a population of about 100,000 or more to avoid a buildup of harmful recessives.

I would say you could get by with 2 or 3 dozen will few problems, especially if you screen the group for ‘bad’ genes. Also, you could try to include a group with as much genetic diversity as possible (Include a couple west Africans, east Africans, northern Europeans, eastern Asians, ect.).

According to this site, it appears the lowland subspecies of lowland European bison got down to 36 at the end of WWII - all in captivity. Now, roughly 1,000 animals exist - mostly in the wild in Poland.

IIRC, and I can’t get a cite for this immediately, there is a theory that our ancestors passed through such a genetic bottle-neck on the way out of Africa. Apparently everyone in the world can be traced by mtDNA back to one (?) female primate “Eve” from South Western Africa, between 1 - 2 Million years ago.

That’s not the case with appropriate social safeguards against inbreeding. The Tasmanian Aboriginal population existed at around 5, 000 individuals for over 10, 000 years with no buildup of recessive genes. For a population that was able to increase rather than remaining static far lower numbers would be needed.

It wasn’t 1 million years, but that’s irrelevant. The mitochondrial even has nothing to do with a bottleneck. There were probably tens of or hundreds of thousands of women alive at the same time as ‘Eve’. ‘Eve’ probably didn’t even have more daughters than any of the others and in fact she may have only had one surviving duaghter. All that the existence of ‘Eve’ tells us is that her female descendents subsequently managed to marry into every bloodline on Earth. That may not have happened for hundreds of thousands of years after Eve died. For all we know it may not have happened until this generation.

Granted, but it does prove that if, at the time of “Eve”, she had been the only female primate in existance on the planet, we would still be here, since we are all descended from her and her offspring.

Surely not. Her offspring still needed others with whom to mate, did they not?

Yes, the male primates. There were surely other female primates around at the time, but their offspring are not around today - only the descendants of “Eve” still exist.

The descendants of those other females are certainly still alive. Those other women left many offpsring and could well have many more surviving descendants than Eve. Many of them also had far more surviving duaghters than Eve. And more surviving granddaughters, and great graddaughters and so forth.

Imagine a simplified scenario. The are 4 people in the world: Eve, 1 other women and 2 men. Eve has one female offspring. The other two women have 4 offspring each, 2 male and 2 female. Eve’s daughter marries one of those male offspring and has 8 daughters. The other women of her generation have 2 offpring, all male. Eve’s daughters marry them. Eve is now the only common female ancestor of every family on Earth.

But you will notice that the other women alive at the same time as Eve have left also left descendants. In fact they left far more offspring than Eve did.
I really can’t stress enough that “Eve’ is COMPLETELY irrelevant to the question at hand. Her existence tells us nothing at all about minimum population sizes. You can not use her, as you are doing, as evidence that the human race can repopulate from one female because that is not what her existence tells us. You really do need to understand that at Eve was never the only woman on Earth, nor was she ever mother to all the women on Earth. It was probably only after hundreds or thousands of generations that she became ancestral to all humans. For tens of thousands of years after Eve died there were millions of women to whom she was NOT an ancestor. I really can’t stress that point enough. Eve only became ancestral to all of humanity AFTER all here descendants had mutated so much that they could no longer possibly inbreed. At the point when Eve became the common ancestor her descendants were probably no more similar to each other genetically than you are to a random man from Africa. The only genetic similarity they shared was in fact one tiny section of mitochondrial DNA. In all other respects Eve’s descendants had mutated into completely unrelated individuals.

If you took a cup of water and poured it into the ocean then after a thousand years every glass of water on Earth would contain some of the molecules found in that glass, no matter where you collected it. What you are trying to do Achilles is use that fact as proof that you can produce an ocean from one glass of water. Of course you can’t do any such thing. The glass didn’t give rise to the ocean, it just got mixed into every part of it. In exactly the same way Eve didn’t give rise to humanity, she just got mixed into every part of it.

Thanks for the explanation Blake. Always wondered about that.

You don’t really need all that many people to establish a viable post-crisis population…a few hundred would easily be enough.

However, the main problem is that a technological society would be impossible at that level. Oh sure, you could teach the kids to read, teach them how to fix the gadgets and such, but there would be no more science, no more engineering. Within a few generations people wouldn’t be able to maintain the technology they had.

That’s a fair enough point Lemur. It’s amazing how fast technology can vanish even in fairly large populations. The Tasmanians Aborigines managed to lose even basic Neolithic technology like spear throwers, boomerangs, clothing and even the ability to make fire. That was pretty basic human technology and the population numbered in the thousands, and yet the technology was lost. Reading would help, but reading is so difficult to learn that it would be lost itself in sort order. Agriculture would also help because it gives society the ability to designate some people as official learners and teachers of certain skill.
I would say there is hope of maintaining higher technology levels without a population numbering in the tens of thousands at the very least.

or any number of sci fi authors but clarke has probably done a fair amount of research,lol and yes it wouldnt take many but the question is how much loss would u be willing to accept left that descion. I mean hypothetically if we were all to die how many representatives of each culture would be included , who excluded, would theyre be a special interest group to lobby for lets say inclusion of the eskimos as a cause celeb?
my thought is related to my answer to the dude who wanted to know why there are different version s of the playboy centerfold ya know?? lol

Thanks to all for your answers, very useful stuff. I find it amazing that it could be as little as a few dozen, but of course entirely possible. So am I correct in saying that 500 to 1000 people carefully selected people with genetic diversity would do the job nicely?

Lemur866 I would agree that a society of that size would not be able to maintain the level of technology we have, but with proper documentation, I would think future generations could at least be aware of what is possible and how to achieve when they could or if need be. I’ve thought of many other problems that could occur if this particular situation arose, so I’m solving them one by one. (:

Oh and Blake, the metaphor at the end of your last post is excellent.

Sorry, I’m being slow, second to last.

Uh, jraybebop, what?