Yes, the idea that 50 men and 50 women would make matching pairs would have to be addressed in the story, because it's unlikely. My story is about a small population and the resulting smaller population of teenagers means there is an issue with pairs.
Actually, changing my response. Assuming control over breeding (not the same as love) then 25 couples is sufficient for livestock and such. This is why I was struggling to try and think of cross-generational and other math that accounted for delaying a homogeneous gene pool. Outside of First Cousins, it is not particularly dangerous and by the time the population has sufficient variation then everything would be fine. Such controls and maximizing off spring are most important in the first 3 generations by my thinking, such that afterwards it could open up and be more "natural".
You have a very negative impression of the human condition, and one which seems to be off-topic. The OP was on how quickly a breeding pool of 100 would reach 50 million, not how happy they'd be along the way. I can accept that e.g. intergroup violence could lead to loss of life that would slow down the growth rate, but the OP was looking for justification to reach the target within 3,000 years, whereas @DefinitelyMaybe showed that, given reasonable assumptions, the target COULD be reached in fewer than 500 years; so the premise can cope with a few factors that would slow that rate down. The tone of the post above seems to suggest that 100 people is a group that is especially prone to infighting...but on reflection, it's more likely that 100 people will get on better (or no worse) than 7 billion...so it seems that what you're actually saying is that the current human condition is a sad existence, with rampant suicide. @GingerCoffee , what would be the smallest geneticaly viable population pool? As @DefinitelyMaybe says, Pitcairn started with 24. OK, you've dismissed that as being the most inbred, and likely to be wiped out with some innocent pathogen, but so far that hasn't happened. In the OP's SF future, there may be some form of detector for an invading pathogen, which can be neutralized it before it has a chance to have an impact (Star Trek's Transporter...A transporter is a fictional teleportation machine used in the Star Trek universe. .... and a bio-filter to remove contagious microbes or viruses)
I would have to disagree with your argument, I am saying that is unlikely that 100 people would successfully establish a lasting and thriving colony, despite the best preparation. There have been references to small populations that have survived however we have no data on how many times a small group has been isolated and failed, the occasional success would be expected but cannot be used as justification that it would be repeatable. Now if the OP said they sent out 100 colonies and hopefully one will be successful, the odds are vastly improved. Variety is the spice of life, one hundred people would not provide much variety. We are human and need more than just daily chores to survive in my opinion. Unless you can wind back our mental development to a simpler time, way beyond something like the Amish for example, any colony is going to expect more from life than just exist to continue to exist. For such a small group to get to a space colony, assuming a planet, where millions could survive, that is more than a huge space station, requires advanced technology and it would have to continue to function to provide support for a small group of scientists who have specific skill sets. Life as we now live it requires thousands of skill sets. I think "Lord of the Flies" addressed this particular issue rather well, just one author's opinion of course. The recent TV show "Wayward Pines" also addressed this same issue, their solution was to have a lot of back ups of people in cold storage.
Oh, you must not have read her whole post, where she quotes this thing: What is the minimum number of it would take to maintain a viable gene pool? (emphasis added)
Another issue, the ages of the 100 people. Again it could be written into the story but if these are adults of all ages, some females will be too old to reproduce. I believe numbers like 160 are looking specifically at adults that produced offspring. Even looking at the genetic study suggesting 70 people populated the Americas (and there were Polynesians who made it to South America so I'm not sure what the Native American gene study looked at), that study would be of how many inhabitants had children whose family lines went on to reproduce. And genetic dead ends would not be accounted for in the study of ancestry of the current indigenous populations. In other words the 70 people that all indigenous people (who were looked at) can trace their ancestry back to doesn't include members of the population whose descendants didn't survive to reproduce. For example, if your grandkids had no kids, your genetic line would be a dead end. That could easily happen if something wiped out a large number of children before they reached child bearing age. An influenza epidemic or any other number of disasters could account for only finding 70 ancestors. The initial populations that entered across the bearing straight could have initially been larger but early on only 70 lived long enough to have descendants still alive today.
Cloning would be a game-changer. If people can be cloned, then genetic variability can be preserved. That's even without genetic engineering. EDIT: Cloning may also be able to preserve the genetic material of people who are too old to reproduce, or don't reproduce for other reasons. Also, 160 may give a good chance of survival without cloning. That doesn't mean that 100 is impossible, just that it's less likely. Note that sizeable population increase will help preserve genetic variability compared to a small population that stays small. As less genetic variation will be lost. Personally I think that the OP's scenario is plausible.
I was just looking for a couple of lines of exposition and I got a whole lot more. Thanks you all. Here's the set up for my world. In the nearest foreseeable future, Earth advances enough to establish a self-sufficient colony on Mars. The Earth explodes leaving only the colony on Mars, a couple space stations, maybe a base on the Moon, and a couple of ships. The population might be closer to 200-300? people that are left over. A couple years later a benevolent race of aliens show up and induct what is left of humanity into a galactic federation. My story takes place 3,000 years after that. A 50 million population in 3000 years sound possible to me. Now a couple more questions, while I have you here... Is it possible for the Earth to explode? How? If the Earth exploded would the moon survive? What would happen to it? Does a planet that explodes turn into an asteroid belt? If so, in how long? I'm googling...
Not exactly. It's not that the group would all become the same like stirring a mix and getting a uniform result, though that would happen to some extent. The human genome has about 3 billion base pairs of nucleotides. The smaller the population the less variation that exists in that population to begin with. Preserving individual variation is not going to expand the variation. Think of it this way, it's a bit oversimplified but it's roughly what happens: Say you are a microorganism and you are exposed to a lethal toxin. Because you multiply so rapidly, a million mutations might occur in your offspring before the toxin can wipe you out. Of those million mutations one might provide resistance to the toxin allowing that single organism to repopulate the place with toxin resistant offspring. Now take a human population exposed to a lethal toxin (or infection). There is no time for a million offspring to be born for that one mutation to emerge before the population is wiped out. So you need those million mutations to already exist within the population in order for some people to survive the toxin. People tend to think of mutations as resulting in major birth defects but that is only a relatively few major defects. Minor mutations may do nothing more than slightly alter a protein surface of a white blood cell like the CCR5 deletion does. It is believed that alteration offered some resistance to the plague back in the Middle Ages, amplifying the existence of the mutation in the population. Fast forward a few centuries and it turns out that minor protein variation offers some resistance to HIV being able to enter the cell it needs to access to initiate infection. It's not 100% protective, but it's possible another mutation if it exists within the population, might be even more protective. The point is, the resistance has to already be in the population before the exposure to the toxin, because with slowly reproducing animals there is not enough time for a resistant mutation to emerge. Therefore genetic variation within a population is a critical feature for survival of a species.
I think you misunderstand me. Cloning will not expand the genetic variation of the population; I never claimed that it would. Cloning can prevent genetic variation being lost. The problem with small founder populations is that genetic variation is lost.
I didn't misunderstand you. Losing genetic variation is not the problem. Not having enough of it in the first place is the problem. The genetic variation is lost by the fact the population is too small to contain much of it. Cloning is even worse as you really limit variation when you do that.
This hits on my point with culture. 100 souls would have a frigid culture. Selfish, isolated, dependent, and controlled. Freedom comes from masses, control comes from few. A king rules a small kingdom, but the people rule the world in numbers.
100 people would have a reasonable amount of genetic variation. If there wasn't any loss of genetic variation, a population of 100 would have a good chance of growing to a large size population. It's because genetic variation is lost through random effects that larger founding population sizes are needed. If genetic variation is not lost, there is no reason why the eventual population of 50,000,000 people wouldn't be as healthy, on average, as the original 100. I wasn't suggesting cloning as the sole means of reproduction but in addition to standard reproduction. To prevent genetic loss. If you make sure that clones of every original human are present in the population, then no genetic material has been lost. The clones and those conceived naturally could still continue to mate. Though, as the population continued to expand, assuming the populations aren't reproductively isolated, cloning would become less important very quickly. Wild animals have more need for genetic variation that an advanced species such as humans. This is because wild animals need to be able to adapt to changes in the environment. We can mould the environment to suit us using our technology. Wild animals do not have medicine, nor medical technology, and hence cannot cure illnesses and plagues. Wild animals also live in environments with limited carrying size, so they cannot grow to large sizes. The OP's scenario, which I still think is plausible, plunks them down in an environment that can support 50,000,000 individuals.
Top of my head: I'm sure it's possible for the Earth to explode, but I can't imagine how its own internal forces could cause such a thing. It would have to be through impacting a much larger body, e.g. maybe a rogue gas giant wanders into the solar system and Earth is sucked into a collision. But, that would almost certainly destroy the moon as well. Also, it would be hard to not see such a thing coming from a long way off, so maybe Earth would have time to evacuate at least some people. And it might affect the orbits of other bodies in the solar system, depending on the path it took. If somehow the Earth exploded from internal causes (or maybe humans develop and misuse the Illudium Q-36 Explosive Space Modulator to cause this?), the moon would probably be intact, but without the Earth to orbit around it would go zooming off in a random direction. I imagine it would eventually settle into a new, stable orbit around the Sun (or maybe another planet, but I doubt it) but not until it got done pinballing around the solar system for a while. There are also small but non-zero chances that it would impact the sun, another planet, or be gravitationally ejected out of the solar system. Again assuming the Earth is destroyed by something other than impacting a larger planet, depending on the force of whatever blew it up it would form a rubble field generally expanding outward. Some (but certainly not most) of the leftover bits might form a small-to-medium sized asteroid field in Earth's former orbit, but I imagine most of it would disperse into a bunch of new heliocentric orbits, or crash into other stuff. Anyway. This is all just gut feelings about what would happen, I haven't done any calculations but a lot depends on the initial set up, where the other objects of the solar system are etc. And of course it assumes you want to keep things within the known laws of physics.
Any small population is at risk of being wiped out. You are arguing that nothing untoward would happen. I don't agree. I do agree to disagree and it's time to end this debate.
Actually, I just thought of a correction to my above post. The rubble field left over from Earth exploding wouldn't necessarily disperse into an asteroid field. It would if the explosion were powerful enough, but a less-powerful explosion could shatter the Earth but leave the fragments traveling slowly enough to re-coalesce into a somewhat smaller-than-Earth-sized lump. The atmosphere, magnetic field etc. would be gone and it would just be a dead lump of rock, and its orbit might change a bit as well. I also think the moon would still wander off before it re-coalesced. But it is a possibility, depending on how powerful the initial explosion is.
I am not arguing that nothing untoward would happen. I'm just saying that provided that the loss of genetic variability is avoided, that a population of 100, 50 males and 50 females, could expand in the way that the OP suggests. It's plausible, which is all I am saying. There is no guarantee that any sized population would survive anywhere, but that is not the topic of discussion here. The OP asked whether it was plausible that a population of 100 could grow to 50,000,000, and how long that would take. One of the problems in this thread is that you have paraphrased what I'm saying, but done so inaccurately. That does make it difficult to 'agree to disagree', as you are disagreeing with things that I never said.
@DefinitelyMaybe. You've failed to address the key issue, the genetic variability doesn't exist in a small group. Preserving what doesn't exist is not responsive to what I've posted. That's why I see the discussion going nowhere.
I did address what you said. Up further in your last substantive post, you gave an example of bacteria mutating allowing the species to survive a toxin because mutations in the population may allow some individuals to have gained immunity. In direct response to this, I pointed out that animals do not have the ability to manipulate their environment, and are therefore more suspectable to changes in the environment. The animal needs to adapt. To adapt, they need genetic variability. Humans who have intelligence and high technology are different because we can adapt our environment to suit ourselves. We also have medical technology, and are therefore much more capable of meeting biological threats. Etc. It's very different for humans than it is for even other mammals, let alone bacteria. We have technology, culture, we have species memory where things learned can be spread around. Even a simple technology such as building fences can allow us to meet certain types of threats, and we have far, far more advanced capabilities than that. Provided that the genetic variability in the population is maintained, there is no reason why the average genetic fitness of the population must decrease over time. Note that at all times I am saying that it is plausible that the population could survive and increase in numbers as wanted by the OP. Since we are talking fiction, we don't need it to be probable that this would happen, only that it be reasonably plausible. Now, you're saying that decrease in genetic variability isn't the issue, but the small amount of variability in the initial population. If the discussion is to continue, what I think needs to happen is that you need to explain why a human population of 100 which has technology and an understanding of genetics wouldn't be able to survive. Examples from the animal kingdom where mutations are required to adapt to threats are not, in my opinion, sufficient because we as humans have other ways of responding to threats other than biological adaptation. E.g. developing new technologies, developing different ways of living off the land. I'm not ignoring your point, I am addressing it. What I would like from you if you are to continue the discussion is the description of why the small amount of initial genetic variability must mean that the population cannot grow.
Easy answer: Schizophrenia. We don't know what causes it, but there are indications that a simple viral infection (any virus) during pregnancy might be the cause. Once that develops a scizophrenic has a 25% of passing it on, and a 30% chance of passing on a different mental illness. If both parents have it the chance tripples.
Since the OP has given us a lot more critical detail about the storyline the question of whether 50 couples could eventually grow to fifty million over a long period of time seems feasible. Having an advanced alien life form taking them in and nurturing them along certainly changes the issue. At this point I think the OP was just looking at how the Earth's population has grown over many millennia and trying to parallel that to some extent, just my opinion. As far as the new questions that Vito has posed sounds a lot like the Hitchhikers Guide to the Galaxy premise with the hyperspace bypass construction crew having a bit of remorse. And for DefinitelyMaybe maybe you should work out your math for the old TV show Destination Moonbase Alpha (1978), what would their population be now?
@tonguetied That's exactly what I did. I just looked at a world population graph over the past couple of centuries and made a guesstimate. I read Douglas Adams when I was in high school. I knew I was subconsciously ripping off the idea from somewhere, ha. I picked 3,000 years because I figured that was a good length of time for people to forget about what happened to Earth. They view old Earth as mythical with a questionable past. No one really knows how life on Earth was before the explosion.
We differ in that I believe you are overestimating the ability of humans to overcome newly emerging pathogenic microorganisms with technology. You could certainly write a fictional story where we can. But in the real world technology is a long way from achieving such feats. We have examples in recent history of what happens to small populations when new highly pathogenic microorganisms are introduced. A strain of influenza wiped out whole populations in small villages in AK in 1918. The 1918 flu pandemic: If a new epidemic pathogen emerged such as it does on a recurring basis with influenza, those 100 people could become 10 long before a treatment or vaccine for the pathogen was developed. Lest you think 100 years has passed, that couldn't happen today, you'd be wrong. And you are assuming 100 people can carry on medical research that today takes thousands of people and many months to develop a treatment for a single new pathogen. We have yet to conquer the threat of a newly emerged influenza strain. SARS was a recently emerged virus that killed a couple thousand people before we got a handle on it, including killing 800 health care workers who were knowledgable about infection control measures. Despite ebola not being the risk to the general population that the news media hyped it up to be, the fact two nurses in modern equipped hospitals were infected highlighted just how flawed our infection control procedures were. In addition to the variation not existing in the initial population of 100 people, it takes thousands of years for that variation to become reestablished even when the initial 100 people grow into a larger population. What happens to a population that starts out with a small initial gene pool? Again you have to consider what is likely vs what is remotely possible if one draws all the right cards. Realistically, a small population of any mammalian species, including humans, faces tremendous odds. We write fiction. To make such a story believable, I would consider what is likely to happen and note how it was dealt with. Otherwise people will see the plot holes and fault you for them.
This was calculated back in 2002, but I think this is just what you ordered OP. "Magic number" for space pioneers calculated But they also mentioned that to prevent inbreeding problems, an original group of 160 should interact with an outside population (i.e. returning to Earth) after 200 years. Like some other people pointed out, otherwise everyone eventually will be related. If you look at royal families and the breeding of endangered animals by zoos for example, they end up with many hereditary illnesses since "weak" genes are passed on and amplified. For a closer example, just look at dog purebreds like the golden retriever.
@GingerCoffee I went and re-checked the original post, and we are talking about a space colony. This means that the disease situation is very, very different from what it is for isolated human populations on Earth. On Earth, there are reservoirs of infection and infectious agents that have evolved to attack humans and other mammals. Reservoirs of infection can be human populations, but for many diseases (e.g. the flu) reservoirs of infection are found in animal populations as well, e.g. birds. A space colony would only have the diseases that they take with them. If none of the 100 have the flu when they go, or at any time all of them are free of the flu, then that disease will not be present in the founding population, and hence will never be a threat. Even diseases that they did take with them can be eradicated if all members of the population recovered at one time. Some can survive for a long time in graves, e.g. anthrax, but careful treatment, e.g. cremation of corpses could assist here. It's plausible that the population will be clean of infection, even unto the common cold, at some point before or soon after colonisation. If there are native organisms on the planet where the colony is established, then it is very unlikely that they will be able to attack humans. E.g. viruses use the host cell's mechanisms to reproduce. Retroviruses actually insert their DNA into the host DNA to reproduce. Extra-terrestrial viruses would be extremely unlikely to be able to infect humans as it seems unlikely that the biological mechanisms and materials (e.g. the DNA, RNA, proteins, or what takes their place in extraterrestrial organisms) will be compatible. Even if we're talking about bacterial infection, or similar more independent extraterrestrial organisms, the organisms that infect us are evolved to do so. Depending on how different the underlying biology is, it could be reasonably easy, up to near impossible, for alien bacteria to evolve to be able to infect us depending on the biologies in question. E.g. I'm not sure that I think that silicon based life is possible, I think that all life in the universe is likely to be carbon based. But if we did have a silicon based biology, humans would be highly inorganic to them and it may be that such life will never evolve to infect humans. Let alone in 500 years or less. Even carbon based space life may be different enough from us that it may take a long time for extra-terrestrial bacteria to be able to use us as hosts. We will take organisms with us, e.g. in our guts. But, the emergence of brand new infectious bacteria is rare, even with the numbers of humans we have. Diseases which are new to us typically have jumped a species barrier, and Certainly it's plausible that this could be difficult enough for an initial population of 100 to remain disease free for five hundred years. Bacterial diseases new to us typically have jumped species barriers or have changed their method of transmission so that a rare disease becomes an epidemic. A space colony may take livestock with them, or companion animals. But, they could set up a purely vegetarian colony. Or, they could take steps to make sure that their seed livestock population is clean, either on arrival or at some time after arrival. There are ways that a space colony could be set up as a disease free environment without external reservoirs of disease, deliberately or fortuitously. Saying what would happen to an isolated population on Earth is only partially relevant, as we're talking about a space colony with a small founding population. The situations are very different. Depending on the alien biology that the founders find themselves in (colonising a lifeless planet would be difficult as it's unlikely there would be a breathable atmosphere), it's highly plausible that there would be no infectious agents that could attack them, and it may well take a very, very long time for such agents to emerge. This is one reason why the "magic numbers" of population sizes may not apply to a space colony, is because these numbers are calculated for species on Earth, and the situation of a space colonly could be very different. I agree that there is the potential for unstoppable epidemics on Earth even with modern medicine, but the same does not have to apply to a space colony due to plausible lack of disease reservoirs and potentially disease-causing organisms.
