What is the minimum number of humans possible...

[SicOne]

...to re-establish the continued viability of the species, in the event of some planetary catastrophe?

For example, if you were to procreate within a family, there is a great risk of genetic problems, but the larger the available gene pool, the greatly reduced risk of genetic problems. I am wondering, for the scientifically-inclined of you (and I'm certain the less-scientifically-inclined among you will chime in with your $0.02-worth...), what the minimum number of humans possible is to basically repopulate the human race over time.

This question actually came up in relation to two TV episodes, one Trek and one not. The ENT episode "Twilight" had some 50,000 humans being convoyed to a planet in the Ceti Alpha system after the human race having been nearly exterminated by the Xindi. Pretty much the same theme recurs throughout the recent Battlestar Galactica series, though I remember a line in BSG about them thinking that the 48,000-odd survivors from the Colonies might not be enough to jump-start the human race after all.

The scenario I am imagining is similar to what could be expected of Voyager, stranded with permanently-inoperable propulsion in orbit of a suitable M-class planet. At first glance, the crew of Voyager appears to be predominately male, but there have been enough females mentioned that viability may be sustained for several generations, perhaps enough time for the Federation to find the nascent colony several decades or a few centuries down the line.

I know much depends upon the number of males versus number of females, respective ages and fertility...consider my question to be related to humans-only (no interspecies hybrids) of peak procreative age (early 20s to early 30s), in good health, with access to modern-Trek-times (2380s) medicine and technology (genetic/eugenic tampering/altering aside), and in equal gender numbers....though feel free to speculate on the results on, say, one male to every three females, etc.

 

[Timo]

Before the real-world experts chime in, I'd want to say the fictional medical technology of Star Trek would be the decisive factor. Five people would be too little, given 21st century tech, as "Up the Long Ladder" establishes; but ten, given 24th century tech, might do well in artificially broadening their genetic variety for future durability and flexibility of the species. Although to be sure, Pulaski never offered any 24th century medical technology solutions to the "replicative fading" problem inherent in the 21st century tech - but then again, she wasn't interested in helping out these people to start with.

If 24th century technology continued to be available, then genetic diversity need not be relevant, of course. The people could remain genetically inflexible and unable to adapt to changes in their environs, but the technology would prevent such changes, and would negate the problems of unfavorable genetic variation even when there was no favorable variety to compensate.

Timo Saloniemi

 

[Christopher]

http://en.wikipedia.org/wiki/Minimum_viable_population

http://ask.metafilter.com/50835/Oops-I-destroyed-the-worldagain

It could be anywhere from a couple dozen to a couple thousand, depending on whom you ask and what parameters you take into account. It's believed that humans were almost completely wiped out once and that all living humans descended from a group of just a few dozen individuals. But the larger the population, the safer from extinction it is.

Also the safer from mutation, which can be good or bad. It depends on whether you're willing to take a gamble on evolution. Near-extinctions can promote evolutionary change, because new mutations that are unnecessary for survival or overly complex tend to get outcompeted by simpler, more basic genes in a large population but have more chance of propagating widely in a small population. And sometimes those genes happen to introduce a new potential that proves beneficial. But they could also be harmful, which is why inbreeding is generally regarded as a bad thing. Small population size may have promoted the spread of mutations that led to us, but that doesn't mean the gamble's going to pay off most of the time. As a rule, you're safer sticking to a larger minimum population.

 

[USS Triumphant]

In jr. high, I calculated this question out, and came to the conclusion that you could repopulate the species with 8 males and 2 females, with broad genetic variation between the initial subjects. That would be a dangerous minimum, though, as it assumes continued good fertility and health for all involved, with no accidents, for at least the first two generations of offspring, and a willingness for everyone to mate with anyone not related to them closer than 5 generations. Conflicting personalities could kill the species, with the bare minimum number in play.

If asked to create an Ark project, without being allowed to do any additional consultation with experts (which I certainly would do, otherwise), I would probably try to do at least eight ships (or whatever) for redundancy, each containing at least 24 males and 24 females (also for redundancy). That would be a minimum total of 384 people.

 

[Miss Chicken]

I read somewhere, I am not sure where, that about 500 is a good number. Much below that number and there would be a good chance of an "evolutionary bottleneck" forming but with a minimum of 500 there would be enough genetic diversity for the population to stay reasonably healthy.

 

[ancient]

Before the real-world experts chime in, I'd want to say the fictional medical technology of Star Trek would be the decisive factor. Five people would be too little, given 21st century tech, as "Up the Long Ladder" establishes; but ten, given 24th century tech, might do well in artificially broadening their genetic variety for future durability and flexibility of the species. Although to be sure, Pulaski never offered any 24th century medical technology solutions to the "replicative fading" problem inherent in the 21st century tech - but then again, she wasn't interested in helping out these people to start with.

It's possible that those 5 survivors were related.

Say, 2 pairs of siblings and one other guy, that makes the gene pool even shallower.

 

[darkwing_duck1]

Something no one in this thread has yet considered is the difference between aboriginal man and modern man.

Modern man is far less ecologically integrated, not to mention in many ways less biologically capable, than his forbears, and thus the minimum population to sustain him is going to be much higher than mere genetic variability.

 

[SicOne]

Thank you to everyone who has participated thus far, and contributed links to several interesting sites. It would seem the numbers fall between the 150-ish crew of Voyager and the 50,000-ish survivors in Battlestar Galactica. Many variations occur also based on available resources and technology; the overall tech level of BSG (jump drive not withstanding) being roughly analogous to our own. Probably a better example of what I was looking at for Voyager was more of a "what if the Kazon were ultimately successful in stranding the crew on the planet in "Basics"?"

Christopher, the thorough answer you provided seemed to suggest you have thought about this topic as it related to Trek before...

T

 

[JNG]

I wonder to what extent alien genes in the mix would complicate the stranded-Voyager scenario.

 

[Christopher]

Christopher, the thorough answer you provided seemed to suggest you have thought about this topic as it related to Trek before...

Does it? No, I haven't. It's just a general-science answer. I mean, I based the discussion in real evolutionary science, which is about as disconnected from Star Trek as you can get.

 

[captcalhoun]

according to the Architect in Matrix Reloaded, 23. 16 female, 7 male.

 

[kv1at3485]

0 if you have a genebank and other technology (AI's/automation) to grow and raise the resulting vat grown individuals.

 

[SicOne]

Hmmm. Couldn't some of Khan's people have thrown a few hundred genetically enhanced humans into a sleeper ship and sent them on their merry way, programmed to come back to Earth in a few hundred years, in the chance that Khan thought he might lose the Eugenics War? I could see him deciding, if he were definitely losing, releasing some kind of plague to decimate the human race, and his sleepers coming back in Next Gen time to repopulate a quiet Earth.

 

[Bonzo the Fifth]

Hmmm. Couldn't some of Khan's people have thrown a few hundred genetically enhanced humans into a sleeper ship and sent them on their merry way, programmed to come back to Earth in a few hundred years, in the chance that Khan thought he might lose the Eugenics War? I could see him deciding, if he were definitely losing, releasing some kind of plague to decimate the human race, and his sleepers coming back in Next Gen time to repopulate a quiet Earth.

Khan was way too arrogant for something like that to have happened... In his eyes, his victory was inevitable, with no need for backup plans. Any 'sleepers' he sent off to come back at a later date would have only been seen as potential trouble down the road, especially if they grew ambitions in the meanwhile...

 

[Bonzo the Fifth]

It does sort of lead into a related question of 'what sort of genetic improvements could be naturally introduced into the human genome via breeding, as opposed to genetic engineering?'. In other words, what sorts of adaptations could future evolution of the human race involve? I had to do a paper on human brain evolution last semester and found, for example, that barring some novel innovation in design, our brains are likely as large as they're ever going to get (no Talosian superbrains in our future, sadly). I wonder what limits/potentials are still lurking around in the human design, waiting to express themselves... (and I don't mean silly X-men style adaptions. Real ones).

 

[Bonzo the Fifth]

Going back to the original question, there's a part in that that's intriguing from a theoretical standpoint. In BSG, they do have nearly 50,000 survivors, which, in theory, should be enough to keep things going, so to speak... However, being stuck on those ships in little enclaves, essentially, likely would severely inhibit gene flow for the majority of the population (since I'm sure they don't really have a huge amount of nonessential intership traffic for obvious reasons). I wonder what sort of founder effect that might set up in the long term, if they were forced to remain in space for generations (a very unlikely scenario, I know, but an interesting question from an evolutionary standpoint).... I've always had a fascination with future trends in human evolution, so I guess I spend more time thinking on these sort of things than most, though...

 

[Christopher]

It does sort of lead into a related question of 'what sort of genetic improvements could be naturally introduced into the human genome via breeding, as opposed to genetic engineering?'. In other words, what sorts of adaptations could future evolution of the human race involve? I had to do a paper on human brain evolution last semester and found, for example, that barring some novel innovation in design, our brains are likely as large as they're ever going to get (no Talosian superbrains in our future, sadly). I wonder what limits/potentials are still lurking around in the human design, waiting to express themselves... (and I don't mean silly X-men style adaptions. Real ones).

Well, there is no "upward" direction to evolution. It's simply a process of adaptation to one's environment. Where we evolve next depends on what demands our environment imposes. Since we became civilized, we've actually been evolving faster to adapt to that radical change in our lifestyle; for instance, the gene for lactose tolerance in adults has spread rapidly since the domestication of milk-producing livestock.

So one shouldn't expect "improvements," except in the sense of becoming better-adapted to whatever environment we're in. If anything, civilized living has led to a reduction in human strength and durability. Our bones are thinner, analogous to those of a domesticated animal in contrast to a wild one. Perhaps that's more nurture than genetics; since we don't need to exert ourselves as much to survive, we don't undergo the same amount of physical activity and stress that encourages the growth of heavier, stronger bones. But it shows that there's no reason to expect evolution to "improve" us in the conventional sense, like making us stronger or smarter or giving us keener senses. Except in the sense that the evolution of our brains and hands has given us the ability to invent technologies that increase our power. Since that's the evolutionary direction our species has taken, it's unlikely that we'd naturally acquire any new power within our own flesh.

In BSG, they do have nearly 50,000 survivors, which, in theory, should be enough to keep things going, so to speak...

Actually, as of last night's episode, it's down to 39,644.

 

[Bonzo the Fifth]

Well, there is no "upward" direction to evolution. It's simply a process of adaptation to one's environment. Where we evolve next depends on what demands our environment imposes. Since we became civilized, we've actually been evolving faster to adapt to that radical change in our lifestyle; for instance, the gene for lactose tolerance in adults has spread rapidly since the domestication of milk-producing livestock.

So one shouldn't expect "improvements," except in the sense of becoming better-adapted to whatever environment we're in. If anything, civilized living has led to a reduction in human strength and durability. Our bones are thinner, analogous to those of a domesticated animal in contrast to a wild one. Perhaps that's more nurture than genetics; since we don't need to exert ourselves as much to survive, we don't undergo the same amount of physical activity and stress that encourages the growth of heavier, stronger bones. But it shows that there's no reason to expect evolution to "improve" us in the conventional sense, like making us stronger or smarter or giving us keener senses. Except in the sense that the evolution of our brains and hands has given us the ability to invent technologies that increase our power. Since that's the evolutionary direction our species has taken, it's unlikely that we'd naturally acquire any new power within our own flesh.

Of course there's not a 'direction' for evolution (at least, not in the 'intentionality' sense of things. That doesn't mean that natural and artificial forces aren't setting things up for future adaptations to express themselves...

As your example of lactose tolerance goes, there are still selective pressures on humanity, even though we've managed to overcome many of our biological weaknesses over the last several thousand years. We also have the additional benefit of being able to 'manually' overcome our biology, with tools, creativity, etc., and not just be unwitting victims of it

I suppose talking about future human evolution from a strictly 'natural' standpoint is a bit of a flight of fancy, though, since, no matter what adaptations could have arisen naturally, it's pretty much inevitable that, barring some collapse of civilization, any significant developments in the human genotype are going to come from us, as natural evolution is far too slow to compete with our genetic engineering capacity.

And assuming that civilization DID collapse and we no longer had that benefit, then a whole new set of selective pressures would be driving us at that point.

I suppose, evolutionarily speaking, I like to think about what people 'project' our species could become and contrast it with how possible it is for it to be, especially since most people don't seem to understand how many of our biological limitations are things that simply won't be solved naturally, only artificially.

In BSG, they do have nearly 50,000 survivors, which, in theory, should be enough to keep things going, so to speak...

Actually, as of last night's episode, it's down to 39,644.

Good point... Still a sufficiently large number, though, I would think, especially if they'd just settle somewhere, already (I get the feeling they won't be staying on the planet they're on at the moment.)

 

[SicOne]

Good points, Bonzo and Christopher.

In relation to BSG, yes, they are stuck in little enclaves...and I have to wonder how many females of reproductive age Baltar has smuggled away in his little harem?

Or what the guys on the prison ship would do if they knew about it.

Roslin said, in the pilot, that they needed to get away from the Colonies and start having babies. One has to wonder if there is a section on Galactica dedicated to this purpose, a birthing area. Think about it...Galactica has a medical bay, whereas people are pretty much jam-packed on the RTF. Galactica is the best-protected ship in terms of armanent and armor, and I can see a plan in which an emergency situation would lead to females and babies being taken to Galactica in case the Cavil faction appears and starts lobbing nukes at the fleet. Granted, it would take time and effort; wouldn't be a Trek-thing, such as transporting all of them aboard at the last minute en masse.

OK, off-topic...is Ellen Tigh the last Cylon, or is Starbuck? Tigh said it was Ellen, yet we saw Thrace burn up her old body.

 

[Christopher]

That's way off-topic, but...

Spoiler: BSG

Ellen was the last of the Five; her original died 2000 years ago. But Kara seems to have been newly downloaded at the end of last season -- there were twelve known models, and she's a new addition, a thirteenth. At least, that's how I see it.