How long would it take a space colony of 100 modern-day people, 50/50 m/f, to reach a 50 million population? Would there be rules for procreation? What about in vitro fertilization? Inbreeding? All humans are dead, except for the 100. All of them are scientist educated types. All men are virile and all women are fertile. The goal of the colony is to repopulate humanity.
Assuming that each family has four children on average, that would mean that the population will double each generation. As there will be four children to replace two adults. The reality will be more complex, but hopefully effects such as people who don't reproduce are balanced by families with larger numbers of children. That means that the population after n generations will be: 50 x 2^n x = multiply where ^ = "to the power of". We want to know when they will reach 50,000,000, so we create the equality 50,000,000 = 50 x 2^n To solve for the number of generations required, we solve the inequality for n: => 50,000,000 / 50 = 2^n => 1,000,000 = 2^n => n = log2( 1,000,000 ) where log2() is "logarithm to the base 2" => n = 19.9315685693 Or about 20 generations. Assuming that a generation is approximately 28 years on average, that would mean it would take approximately 20 * 28 = 460 years. Clearly different estimates can be found using different numbers for how much the population will increase each generation, and how long an average generation is. Minimum viable population is more difficult, and 50 seems too small. However, it's possible that your population could survive.
Wow, that was awesome. 460 years then. What would the population be in 3000 years for those same 100?
100 x 2^(3000/28) = 1.7914877 x 10^34 That's assuming exponential growth with no limit. I think that there is nothing in the universe big enough to hold a population of that size. BTW: Pitcairn Islanders founded a population with 12 men and 12 women, which has survived. BTW2: I made an error in my original calculations. It's 100 people originally, not 50. So, it would take one generation less to reach 50,000,000. Or about 432 years. In reality, populations don't grow that quickly as when the population gets large, other effects kick in. Like lack of food.
Thank you, sir. I'm setting up a situation in my story and I'm trying to figure out how to explain it. I wanted to say 3000 years, now it seems like too much. I wanted 100 people with modern technology to reach a population of 50 million with high technology in 3000 years. Now I'm thinking around 500 years.
I wouldn't worry about inbreeding. Anyone who can establish a permanent space colony can handle genetic engineering.
Maybe at one time they had to get rid of a chunk of the population because of genetic defects and they had to start over.... So it did take 3,000 years, ha!
It could easily take that long. The need to develop agriculture. Disease. War. There are lots of ways that human population growth can be curtailed or reversed, and we don't seem to ever stop coming up with new ways.
Great Work @DefinitelyMaybe ! However, just because you could reach your target population in 500 years doesn't mean that you would. OK, early generations would be strongly motivated to procreate as much as reasonably possible, but that motivation would erode as it faded from memory. Think about the economic and political drivers going forward. It's likely that smaller families would become more normal as parents tried to reduce the amount by which the family estate was diluted with each passing generation, so a single child might become attractive to retain wealth, and wealth tends to lead to political power... So there's no reason why the figure of 500 years wouldn't stretch out to 3,000 Incidentally, the population of England rose from 7,754,875 in 1801 to 30,072,180 by 1901. Could @DefinitelyMaybe check how accurately that reflects his growth model? ETA: Actually, @DefinitelyMaybe quoted a doubling every 28 years, England doubled every 50 years...OK, this was Victorian England, so any amount of filth-related diseases that - I assume - the advanced civilization posited by the OP would be able to manage without.
What if it were 100 conservatives to start with? 100 liberals? Who would take longer? What if it were 100 christians, or muslims? A 100 communist? How long would it take 100 gay people to reach 50 million in population? Hell, it could be any amount of years and a million ways to get there.
Am I the only one who immediately considers having 2 men take 25 women a year for breeding? If they are genetically different, then anything beyond first cousin status really does not have a significant increase in mortality. Furthermore, if the goal is to produce similar individuals, barring severe genetic flaws... inbreeding is probably fine. My setting does not have 50 million people, but the family lines of one group are very much based on a single male having about 25-30 children a year with women. With more men, this process essentially makes inbreeding a non-event. Furthermore, 28 years a generation? Hmm... If you want to breed a bunch, I'd cut that down and require 80% of women to reproduce once every 3-4 years outside the original population. Easy to hit that number in much shorter time, but resources are going to be the limiter on growth.
Put your limiters on where you want, but the baseline of resources and such will obviously pose a bigger issue then how the child is conceived. Aside from problematic inbreeding, the goal would be to have a higher number of women to men. If a technology exists to skew the normal numbers then by all means... all numbers change quickly. Conditions... conditions... that is where it all matters. Besides, if I was overseeing a breeding program... efficiency would be the ultimate goal. Things like childcare and such work themselves out pretty quickly if you have essentially uncontested expansion and access to plenty of resources. Children become useful for work at about age 7. Sure it would upend the "society" as we know it, but such a case would naturally be far beyond anything we understand now.
It very much has to do with culture as well. What is the society's culture? Is it Patriarchal? Matriarchal? Or is rearing done by a caste of selected eunuchs that are unable to bear children? If a father has many children, then they to may have many children, and so forth the society grows exponentially faster than the society that is with only two children each household. Those two have less genetic mates to choose from, they are culturally taught to think more about themselves than family (as there is only two children to focus on they can grow selfish), those children grow up to want equal to or less children, but on occasion more. If society frowns on any more than two children the growth of the society is stunted and they will die. If the colony has resource allocation problems and logistics cannot be established to compensate for a growing population, children will be limited and it will take longer. If in the former scenario, the family is the focus, then growth would be exponential. I image a world that crews its space fleet with family crews. The mother and father are the masters and commanders of their vessels, their children their crew. Of course, that would need some ironing out, but it could mean a huge society, maybe religious at core to hold such tight values, maybe space gave them a new religion, that breeding to grow into the endless void is necessary. It is culture that can drive or stymie growth over time, but it is one of the many factors involved.
What do you call a hundred scientists in a new space colony? Not a good start. It would be unlikely your colony would survive past a couple of generations in my opinion. Society doesn't exist on scientists alone, Hitchhikers Guide to the Galaxy actually hits on this subject nicely, all the "useful" types die due to a lack of telephone sanitizers or something like that. My point is just like endangered species on this planet, there is a threshold that if you go below there is no return, extinction is inevitable. To start a colony without future injections of humans you would probably need several thousand people with a vast mixture of talents. Where are they going to get new reading material? Scientific American is pretty boring, you are going to need some writingforums members to create new material.
A population of 100 adults is probably too small to be genetically viable. I suggest you put some artificial manipulation of the gene pool in there. Otherwise it won't be long before everyone is related to everyone and inbreeding could be a problem.
Not so well though: Pitcairn is left with the distinction of being the most inbred society on earth. So without contact with the outside world, it's not clear how long they would have survived.
I really have to disagree with that notion because it is not backed by science. Even without any technology, the population would exist just fine from a genetic stand point unless very deleterious problems were already present and were already shared. With a single generation the problem could be rectified and removed by many methods, including sterility or infertility.
With Pitcairn Island, there is the dreadful sexual abuse that was there. Perhaps I shouldn't have used that example due to the sexual abuse. If we use them as an example of a population, they have survived a number of generations. As the population has remained small, they will be far more inbred than they would have been had the population grown considerably. I'll leave that example there and talk about the general case. One problem with small populations is that genetic variability is lost. E.g. if you have two parents and they have only one child, then half the genetic variability of the parents is lost. If they have two children, then about 25% of the genetic variability is lost. If three children, then 12.5% is lost, four children, then 6.25% is lost. This ratio should apply both to a single couple and a population of couples. That's in one generation. If the population continues increasing exponentially, having four children per family on average, then as the number of people has doubled, in the second generation there will only be half the loss of genetic variability. Say, 3.125%. Then 1.5625%, and so on. If I had more time I'd work out the total loss of genetic variability, but it shouldn't be massive. Not like deliberately inbreeding mice so that you get populations where all individuals are genetically identical as all variation has been lost. The problem with loss of genetic variability is that adaptation to changed circumstances relies on genetic variability. If the population gets too small, then genetic variability will be lost, and evolution becomes much, much harder/slower. With lack of genetic variability there's also the risk that a disaster such as a plague may kill off everyone as nobody has rare genetic immunity. One advantage that humans have is that we're aware of these problems. So, it would be possible to be aware of it, and handle the situation. E.g. if they could make sure that everyone had at least one surviving clone, then no genetic variability would be lost.
It is scientific, not sure why you question that. That's a simplistic view of the problem. The reason a population of slowly reproducing life forms (as in years not minutes) will go extinct is not because they'll inbreed until all the recessive genetic defects will kill them off. It's because a small population with very little genetic diversity is at risk of being wiped out by a single outbreak of disease. The isolation on Pitcairn may have allowed them to survive with such significant inbreeding a few extra generations. But all it would take to wipe them out is a single pathogen reaching the island via a migrating bird, sea life, or a visiting human. Whatever the change in the environment from weather to invading species, a population with little genetic diversity is at serious risk of extinction. We have managed to bring back species on the verge of extinction but only with an intense effort. What is the minimum number of it would take to maintain a viable gene pool? With a richly resourced environment, few pathogens and a strong group of settlers, it's possible for a group as small as 70, but that's speculative at this point. North America Settled by Just 70 People, Study Concludes
It is not like we are beginning with 100 people of a single extended family with a pile of genetic defects. Yes, you will have different and various issues, but I do not think it is a fair comparison to draw this conclusion. Animals are different from people. Even if you have limited genetic diversity, it still would work. If you get a bunch of different ethnic backgrounds in the population and draw your lines carefully, inbreeding is not an issue in real life or in this situation. Consanguineous relationships are also practiced in many places and while hereditary hearing loss is part of the Qatari problem, it is an example of non-disasterous genetic faults. The Bedouin population is also full of consanguineous relationships through its history, variation needs to be introduced though a single generation or two is not going to bring doom to all.
I think all the talk of inbreeding, etc. is minor compared to how 100 people are going to interact with each other after even a short period of time. You will never get a group of that size together without a lot of infighting which would eventually escalate into violence and so on. A hundred souls but never a soul mate would be the rule. What a sad existence. Suicide would run rampant in a small period of time.
The populations you speak of have much larger populations they just don't live in the same family groups but they do interact and exchange members. As for, "Animals are different from people," do you not know that human is an animal species? We can take more deliberate actions to manage genetic problems, but I don't think you understand why inherent genetic variation matters. As for different ethnic groups, that may or may not mean you are capturing enough genetic diversity. And it presumes the 100 people were carefully chosen for their genomes. I don't think the survivors would be chosen like that but it could be written into the story that they were selected for their knowledge and their genetics. Qataris are becoming obese, passing on genetic disorders at an alarming rate It's an interesting article in the Atlantic. As for, "The Bedouin population is also full of consanguineous relationships", yes but we aren't talking about intermarriage between close relatives, we are talking about isolated gene pools, a completely different matter. The Bedouin consist of a very large population spread over a wide area. And you note that variation only need be introduced rarely, but that isn't suggested in the OP story premise. In addition, I think you might want to read more on the Bedouin because those tribes as most tribes in isolated areas of the planet have a lot of member exchanges. This is an older paper but we've understood the importance of genetic variation in a population for a long time. Importance of genetic diversity to the viability of mammalian populations
