What is the minimum human population necessary for a sustainable colony?

Question

How many humans are needed in order to sustain and grow a steady population in a habitable area? Assume resources are adequate and the environment is favorable.

To further refine this question, let's assume this is an early spacefaring technology scenario, such as putting a colony on a neighboring planet (same system) with earth-like conditions with a technology level either current or near-future. Assume the population has a mix of professions suitable for the new environment (resource gatherers, physicians, etc.).

Answer 1

This is quite dependent on technological/medical knowledge.

For example it has been calculated at 160 for space exploration, provided the explorers return home after 20 generations. This of course assume pretty good medical availability and actually fairly low risks to individuals. The resultant reduction in genetic variability has been analyzed as not being very detrimental. Certainly it could but not guaranteed to and even small infusions of genetic material would majorly reduce negatives. Also starting out with high genetic variability will help reduce those risks.

A good example of a relatively genetically non-variable population is Ashkenazi jews; a recent study has suggested that in semi-recent history (25-30 generations) their total population was around 350 individuals; yes there are some genetic defects that are common but there is no generalized unhealthyness (or genetic unthriftyness); and some genetic defects are rare because they weren't very present in that initial population group.

I would say that 160 is a fairly good minimum; yes less than that may survive but any minor disaster has a unpleasantly high chance of wiping out the colony.

The lower the technology/medical treatment availability the higher the population would need to be to provide 'buffer' for injuries.

Answer 2

The answer by @Nick Wilde is very good, but the quoted number of 160 (the source actually claims 80 is possible with social engineering) refers to what is minimally required to sustain a stable population for 10 generations.

This could be relevant if your planet would be very far away, however if you look at the distance between Earth and Mars, it just takes about a year to move from one planet to the next. As such, the population that you would need to fit inside the spaceship could be reduced significantly, as you can simply let the population grow on arrival.

It is hard to quantify this effect, but as 80 already can be sufficient for a stable population, I dare say:

Starting out a growing population can be done with less than 80 people, if chosen carefully.

That being said, the main concern seems to be genetic diversity. Sources vary a bit on the subject, but it appears that with the current technology sperm can be frozen for at least 1 generation. So, let's do a quick calculation:

Suppose we need to reach a population with 80 unique genetic sets to go past the tipping point. Let's do a quick calculation on how this can be achieved if fertile women are able to give birth to 4 children on average and have taken a bunch of frozen sperm samples with them:

• Generation 0: 10 (fertile) women and 10 frozen samples
• Generation 1: 20 women and 20 men and 80 frozen samples
• Generation 2: 40 women and 40 men

From this point on the women of generation 2 could continue to expand the population with the men of generation 1 and 2. It is true that a little bit of bad luck could already mess up the system, but being on the safe side it seems like:

A spaceship with 20 women and a freezer full of sperm is likely enough to start a growing population.

Answer 3

15 individuals, 8 males and 7 females are certainly enough to create a sustainable population, capable of growth without any out-breeding, albeit with some genetic diseases due to in-breeding.

The reason we know this is because of a small island on the Atlantic Ocean, Tristan da Cuhna, which has a robust, growing population of 266 (May 2016), and have been inhabited for about 200 years. All people living on the island can derive themselves from 15 individuals, 8 males and 7 females. The population is a textbook example taught in genetics courses.

Tristan da Cunha - Demographics (Wikipedia)

Answer 4

This is known as the Minimum Viable Population, and many computer models and studies based on various circumstances and species have been run.

For Humans, including the desire to ward of genetic defects due to inbreeding the median MVP reported is 4,169 individuals. You can read up more on this on the wiki article here.

Answer 5

As well as the biological, social and genetic diversity issues of maintaining a viable population you also need to consider maintaining technology. Clearly a small colony on another planet is going to very very reliant on technology to survive.

Just for a start it is not difficult to imagine a situation where a new strain of a disease could cut a catastrophic swath through a small colony and even without anything catastrophic day to day illness and injury will be a big strain without adequate medical facilities.

Equally you will need engineers and technicians to keep the basic infrastructure going.

Automation can probably help with this to some extent but it would certainly seem risky not to have a reasonable depth of expertise in how it all works, especially as the generations go by and you want to expand and refurbish the facilities.

So if we hand-wave the technology of actually getting there and assume a level of technology similar to current with reasonably foreseeable developments on an earth-like planet then we can start to get at least some idea.

Medical

In the developed world there are hundreds of medical specialities and we probably have to accept that a small colony won't have the same breadth and depth of expertise and facilities. Here a good model might be a military field hospital as they are designed to be portable and versatile and are well equipped to deal with both traumatic injuries and primary healthcare as well as epidemics and natural disasters which seem reasonable priorities for a colony. So you might have :

• Surgeons
• Anesthetists
• Surgical nurses
• General practitioners
• Dentists
• Pharmacists
• Ward nurses
• Intensive care nurses
• Primary care nurses
• Paramedics
• Specialist cleaning and logistics staff

For a long duration colony you would probably also want lab technicians and medical researchers although these may be part of the science department. Obviously you would want personnel with a broad a range of expertise and experience as possible.

Similarly if you intend to use working animals and livestock you will want a few vets to look after them.

Government and administration

Clearly this depends on how you want the colony to be run but with a military type model you would have something like a regimental headquarters with a commander, adjutant, office staff and probably also heads of the various departments as technical advisers. Police and security may also come under this heading at least in part.

Regardless of the actual system of government you will need at least a few people with administrative and legal skills.

For obvious social and cultural reasons it may not be desirable not to have a purely military culture with absolute authority over the colony but it does make sense as an administrative structure even if you have other more democratic or decentralised checks and balances in place.

Engineering and Logistics

As mentioned the colony will depend a lot on technology which needs to be maintained and you will also need the technical expertise to develop natural resources, construct buildings and infrastructure and set up manufacturing facilities you could also argue that farming and food production falls broadly into this category. Again you have a huge array of specialisations to choose from and there will be compromises to be made between specialist expertise and more versatile generalists. Also each discipline will require theoretical knowledge, technical experience and management and planing. To start with you might set up :

• Maintenance : technicians who know how the various basic systems work and how to maintain them
• Machine and fabrication shop : supporting the other departments in making and repairing parts and eventually setting up a more comprehensive manufacturing base
• Infrastructure and mining : building roads and buildings, mapping and surveying, setting up power generation and distribution.
• Electronics and IT : maintaining and developing computer, electronic and communication systems.

Agriculture

Although you would probably want to mechanise a lot of food production if you end up a planet with indigenous life or at least the immediate ability to support it you will want some specific agricultural expertise. Equally if the planet is sufficiently earth-like some experts in more traditional skills of hunting and living off then land may significantly improve quality of life especially in the early stages.

Science and education

For a multi-generational colony education is clearly vital as you will need to educate the next generation to replace the skills you brought with you. Here you have the potential issue that you have a specific set of requirements in terms of skills but no idea what aptitudes and abilities the next generation will have so your education system will need to be flexible, effective and adaptable.

It will also be crucial that you have an effective way of storing and accessing as much accumulated knowledge as possible. The expertise will be thinly spread so libraries and librarians may be at the centre of the society and the job of librarian may end up as a very specific niche with a very broad spectrum of knowledge.

You would probably also want to have academic/research scientists representing the main branches of science. For reasonable completeness you might have representatives from

• Mathematics
• Chemistry
• Materials science
• Botany
• Zoology
• Medicine
• Physics
• Astrophysics
• Geology
• Meteorology
• Psychology

Obviously there would be additional expertise from the other technical divisions and they might be supplemented by lab technicians and assistants and eventually take on students as part of the education system.

Culture and Services

As well as the basic services required to keep a society running any permanent colony will need to develop culture and leisure facilities to keep the population effective and sane. It is reasonable to assume that these will develop organically to some extent but a few really good chefs and perhaps some resident artists, writers and musicians could well be a reasonable addition to a colony.

Just as an example typical commercial kitchen which could feed a few hundred people to a decent standard might include

• Head Chef
• Sous chef
• Pastry chef
• Assistant chefs (perhaps 3 or 4 to allow for 365 day operation)
• Kitchen assistants (could also be trainee chefs)

Numbers

I've suggested 5 main divisions of expertise and on average it looks like you might want perhaps a dozen or so lead experts in specific fields as well as at least the same number of assistants, technicians and support staff. You might also have a flexible pool of labour from the general population. This also allows for some cross training so there isn't too much reliance on any one individual.

So with this in mind we could perhaps guess that you might have

• 60 or so 'officers' with versatile technical expertise and administrative and organisational roles
• 150+ skilled, specialist technicians
• 300+ general and adaptable labour force with varying degrees of specialisation.

Again going back to a military model a battle-group is typically the basic unit which is more or less self sufficient and consists of around 500-800 soldiers with its own organic logistics and support. Obviously this isn't a very strong analogy to a space colony but it does represent a known structure which is able to function independently long term in a hostile environment with a good mix of specialist expertise and equipment, organisational structures, logistics and versatile labour.

Answer 6

I'm going to ignore genetic diversity because the necessary population to sustain a technological environment will always demand enough people to satisfy that requirement.

Assumptions:

• Maintenance of the basic technology that brought them to the new planet. Not necessarily rocketry... but vehicles, automation, manufacturing, etc. In other words, I'm assuming we didn't spend trillions of dollars to move a population to a new world so they could wear skins and fish with spears sharpened by broken rocks.

• Self-sustaining colony. All the mining, farming, logging, maintenance, manufacturing, etc. must exist within the colony.

• The colonization process brought a single set of all the tools needed to get through, say, a year, but after that the colonists must provide for themselves 100%.

• Automation is commensurate with what's available in 2017. Automation changes these numbers RADICALLY, but the OP doesn't really tell us anything other than it's a intrasystem space-faring society in the near future.

Family Size

Your average family in the United States is 2.53 people. I'm not even going to speculate on what 0.53 people looks like. Worse, even if you round it to 3, that's two parents and one child, which is a decreasing population. You need 4 to break even and 4.1 (better known as 5) to grow. Let's favor 5.

Out of that 5 people let's assume you have two adults, one sub-adult, and two children. That's 2 laborers, one laborer/secondary education, and 2 dependents requiring child care and education.

Your biggest problem is children. They can't be ignored. If you arrive with no children and expect to start making babies you need adults for child care immediately and both education and medical by age 5-6. Therefore, you really must account for children at the outset or your fooling yourself. You could squeeze my final number by minimizing children based on age distribution so that you're getting replacement adults "just in time," but that's much more complicated.

Farming

From here we learn that on average one farmer can feed 155 people. This assumes an established farm in 2010. If we assume the farmer has a family and that he can draw on a "basic labor pool" to get him up and running, then our farmer +4 (family) can feed 150 people or 5:155.

farming = 5T/155 where T = Total population (keep this in mind).

Logging

I thought I could assume if we can get this group to another planet then we can construct with plastic and metal and therefore there is no need for logging. However, it's likely you need crates, paper, rubber, composting, and who knows what other non-foodstuff organics. I can't find statistics for how many people are involved in this. Let's use the farming number and assume one family can serve an additional 150 people with non-food organics. So, another 5:155.

Logging = 5T/155

Mining

This is one of the more problematic issues. Different materials appear in different locations on a planet. This means our colony has many labor centers, all requiring administration, law enforcement, etc. I'm going to define mining as "anything we take from the ground that we can't eat," so it includes petrochemicals.

According to here the average citizen of the U.S. needs 40,000 pounds (20 tons) annually of materials of over 15 types. (I'm being optimistic about the "and other" categories and counting them as one each.)

Mining requires blasting/digging/drilling, hauling, and processing. I have friends who work the hard-rock mines in northern Idaho, and even with automation, they have hundreds of laborers. Granted, it's production mining rather than subsistence colony mining, but still.... Let's assume you need 2 blast/dig/drill, 1 haul, 2 processing for 5 people (25 with families). I must assume a massive ratio or this simply doesn't make sense, so let's assume 25:3000 per item on average.

Remember, that's 2 blasters/diggers/drillers producing their share of 60,000 tons per day. It can be done. I must be done, because...

Total: 825:3000 (see my problem?)

mining = 825T/3000

We need to sub-calculate the number of labor centers for later calculations. That would be T/150 + T/150 + T/2175 = 30T/2175.

Transportation

We need to get things from one place (e.g., farm or mining location) to someplace else (at least another farm or minining location). If we only assume two drivers + families (trucks or trains... pray we're not dealing with trains...) per labor center.

trans = 10(30T/2175)

Maintenance

Keeping the equipment running is a very difficult variable to define. Let's assume two full-time mechanics per labor center.

maint = 10(30T/2175)

Education

The United States has 5.49 teachers per thousand students. We have some austerity going on, so 5:1000. Secondary eduction is 5.5, but this is more important, so 6:1000. Plus families.

education = 55T/1000.

Medical

Keeping all these people alive will be a problem. Keeping them healthy an even bigger one. You've gotta love the CIA, who suggest 2.55 physicians per 1,000 people in the U.S. I doubt this includes specialists and it certainly doesn't account for multiple labor centers. So, 2:1000 MDs and 1 MD per 3 labor centers and 5:1000 specialists. Plus families.

medical = 2T/1000 + 10T/2175 + 5T/1000 ≅ 25T/2175 + families = 125T/2175

Administration

This includes everything from paper-pushing bureaucrats to police, firemen, code enforcement, phone answerers, etc. My right-big-toe tells me we need 3 per labor center + families.

admin = 3(30T/2175) = 90T/2175 + families = 450T/2175

Manufacturing

According to here, manufacturing jobs are 8.5% of the U.S. workforce. Let's assume that's only one parent in a family (like everything else).

manufacturing = (0.085)T/5 + family = 0.085T

I'm going to assume this number includes drivers, administrators, maintenance, etc. It's going to be a bit low because of the compounding affect of unassigned workers, but all that would happen is fewer unassigned workers increased by the same amount of additional manufacturing jobs. So the total population estimate should remain "accurate." (ahem).

Entertainment

I'm going to ignore entertainment of any and all kinds. Colonists should plan on bringing kazoos.

Unassigned Workers

I've intentionally not tried to compound the spouses or sub-adults into the workforce. This is because there will be jobs ranging from street sweeper to technical assistant that I'm not even going to try to estimate. All those jobs must draw from the unassigned labor force (and sub-adults, as necessary).

What am I missing? I'm missing retail outlets, which would presume some kind of town or village. For an initial colony, central distribution or coordinated transportation could solve this until the community begins to grow. I'm sure I'm overlooking/ignoring a lot of other things, but this is a long enough post.

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That's a mess... how do you calculate the minimum population?

• We're going to iterate through the equation.

• We'll use T=1 to find our starting point and ignore the divisors so we have one of each primary laborer plus their family, which means our "initial population" is 2,070. We know this isn't right because we don't have enough raw goods to feed/supply all those people.

• We want to assume that we never increase a number unless the population has actually exceeded the amount required for the increase. No fractional doctors, please, otherwise all the fractions add up to wholes that run out of control. However, this means people are a bit overworked... but that might be expected on a new colony.

• With the exception of our raw materials. We must have enough farmers, loggers, and miners. So we'll round those numbers rather than keeping them at the floor.

Total minimum population: 2,260

• Children: 904
• Sub-adults: 452
• Unassigned Workers: 452
• Farmers: 14
• Loggers: 14
• Miners: 123
• Transport: 61
• Maintenance: 61
• Education: 24
• Medical: 25
• Administration: 92
• Manufacturing: 38

Is this realistic? To be honest, in real life you probably need 10X this number of people... but I can't prove it without spending 10X the time to analyze the situation.

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My Program (PHP)

$a = 100; $t = 1; $ifar = 5; $ilog = 5; $imin = 825; $itra = 300; $imai = 300; $iedu = 55; $imed = 125; $iadm = 450; $iman = 5; $t = $ifar + $ilog + $imin + $itra + $imai + $iedu + $imed + $iadm + $iman; $count_check = 0; $count_max = 1000; while($a > 0.01){ $far = 5 * round($t/155); $log = 5 * round($t/155); $min = 5 * round(165*$t/3000); $tra = 5 * floor(60*$t/2175); $mai = 5 * floor(60*$t/2175); $edu = 5 * floor(11*$t/1000); $med = 5 * floor(25*$t/2175); $adm = 5 * floor(90*$t/2175); $man = 5 * floor(0.085*$t/5); $pop = $far + $log + $min + $tra + $mai + $edu + $med + $adm + $man; $a = abs(($pop - $t)/$t); $t = $pop; if($count_check >= $count_max){echo "\n\nFAILED TO CONVERGE!\n\n"; exit;} $count_check++; } echo "\n\n"; echo "Total Population:\t".$pop."\n"; $children = 2*$pop/5; echo "Children:\t\t".$children."\n"; $subad = $pop/5; echo "Sub-adults:\t\t".$subad."\n"; $spouses = $subad; echo "Unassigned Workers:\t".$spouses."\n"; $far /= 5; echo "Farmers:\t\t".$far."\n"; $log /= 5; echo "Loggers:\t\t".$log."\n"; $min /= 5; echo "Miners:\t\t\t".$min."\n"; $tra /= 5; echo "Transport:\t\t".$tra."\n"; $mai /= 5; echo "Maintenance:\t\t".$mai."\n"; $edu /= 5; echo "Education:\t\t".$edu."\n"; $med /= 5; echo "Medical:\t\t".$med."\n"; $adm /= 5; echo "Administration:\t\t".$adm."\n"; $man /= 5; echo "Manufacturing:\t\t".$man."\n"; echo "\n";

Answer 7

It would take quite a few indeed, potentially more than the 80-160 otherwise suggested. This isn't just about genetic diversity, "spares" and the like, but about all the tasks the colonists would have to do. Even travelling a short distance, you have to have someone up there for every specialist task possible.

Even assuming you don't take enough people to perform what we would now consider basic medical treatment (for example), you still need to have -someone- up there capable of diagnosing basic medical ailments, even if you've got no surgeons, anaesthetists, nurses, gynecologists, maternity staff, etc.

While people can be trained to do a job, they'll be sub-par, and you can expect a few more casualties as a result. Jobs like plumbers, engineers, builders and whatnot would all have to be trained on the new colony, or sent up to form it. Every field would need representation to ensure the success of the colony. I'd venture you'd need a lot more to cover all the things you'd need to get a proper colony running.

As you said, we're assuming all the proper training in the people sent up, but even then, I'd venture you'd need 300-odd to cover all the necessary professions of a colony.

Answer 8

What quality of life and technology level do you want your colonists to survive at?

The lower bound here is not the MVP it's the number of specialists required to maintain the society. If a society of 160 survives, ie the size of a small village, they'll have the technology of a small village, including medicine, education, and life span.

If you want to raise the standard, you'll need more individuals to specialise. It takes many (no idea) individuals doing farming and building before you can, for example, introduce a full time teacher. You will likely need several teachers before you can support some research and development.

Same for industry. You'll need a bunch of miners and lots of farmers before its economically possible to have a blacksmith. And you'll need a good thriving metalwork industry (plus all its consumers) before you can support advanced metalurgy. Technology and development only really takes off when people are able to specialize. In the village, everyones working their ass off in multiple roles just to survive, which makes it tough to advance.

If you want them to use near present day technology, and to keep that tech, you'll need a population of hundreds of thousands, probably many millions. you'll need plastics production, which needs oil wells, which needs engineers and steel construction, you'll need vast amounts of specialist material production (how are they gonna make integrated circuits), tools production, etc etc. eve\ if they start with all of this the stuff will break down and they won't have the tools and reserve parts to repair, until they're all back to Mad Max standards.

Answer 9

Theoretically, you could drive the number lower if you had artificial gestation technology and REALLY good record-keeping.

For example, 4 men (labeled A-D) and 4 women (W-Z) yields:

AW-Z, BW-BZ, CW-CZ, DW-DZ of each gender (assuming you use an X and a Y spem for each pairing).

Answer 10

Assuming the genetic diversity is random and you want them to eventually populate the planet, you want somewhere between 3-5000 individuals. that's the general rule for vertebrates. you need a wide genetic diversity to deal with disease, reduce unintentional inbreeding, and you want enough redundancy to survive a natural disaster cutting the population. the societal constraints are far easier than the genetic ones. http://www.sciencedirect.com/science/article/pii/S0006320707002534

Technological limits are really just having really good data storage and being able to produce enough food. As long as people know what they need to do they can rebuild anything. You assume a colony is going to have to rebuild infrastructure and produce more specialists over several generations. Now if they hand pick the people for genetic diversity you can get away with ~500 but they will be a high risk of failure if an a unanticipated natural (or artificial) disaster occurs. That is the risk with small island population one new diseases or drought can doom them.

Answer 11

If we are worried about genetic diversity, we can always bring with us some frozen sperm. All males then could be made infertile, so only insemination would work. Also, some females could be made to produce babies constantly. So, genetic diversity is not a problem, colony could be kickstarted (and sustained) with only one female and some medical staff. The problem is how to support technical society with such a small amount of people.

Answer 12

1...

There are examples of parthenogenesis and that's what you'd use. Have a genetically problem free female produce a colony of clones. Afterwards you could allow random genetic diversity to recombine sexually a la Komodo dragons. But you'd need a source of males at that point. Which I'd suggest some genetic manipulation for. You'd need facilities anyway at some point in the project to either produce the first parthenogenetic human or to provide self-fertilization facilities.

Now you're only limited by hostility of environment and availability of resources. So you might need more people to rule out chance deaths. But you can definitely go as low as 1. And you can model statistical death pretty well, so that number can be conjured pretty easily. Ex: death by drowning might be 10 per 325 million per day. So I you want a full 100 years of life...

$1 - (1-10/325million)^{(36500)} = .11\%$ chance of dying over your lifetime to drowning.

That seems reasonable. Ascertain all threats, and drive it below a few percent total and I'd say you're probably very well prepared.

But maybe...

0? If you start with no population... but have a robotic nurture-care facility. Then growth via artificial womb isn't a very large stretch. It was achieved in 2013 and the scientist stated the technology involved is as old as Dolly, meaning we could have been doing it since 1996 if not for ethical concerns. Furthermore in 2017 we repeated the experiment and presumably developed it further. So the hardest part in this case is having a robot raise a healthy child. The best part is accidental deaths are mostly inconsequential. As long as the facility remains running you can always try again and hope chance is on your side this time.

Answer 13

The American native peoples are believed to all be the descendants of about 70 individuals who crossed a land bridge from Asia during the last Ice Age (Hey, 2005):

Taken together, the analyses in this study suggest a recent founding of the New World Amerind-speaking peoples by a small population of effective size near 70, followed by population growth in the New World.

It's not my field, but I gather from that article that it doesn't mean there were necessarily 70 in one place at one time; these could represent multiple waves of migration, and of course these 70 "founders" may have come with their children, grandchildren, etc, so the original tribe may have been many more than 70.

These founders were enough to create a fairly diverse number of peoples and civilizations from the Eskimo to the Inca and everywhere in between. However, history has seemed to show that the native Americans were particularly vulnerable to diseases transmitted by European explorers (while the reverse was not true) so you might hypothesize that they had too little genetic diversity and a larger set of founders would have produced hardier descendants.

Bottom line, my answer is: you could do it with two people, but I'd send 100 (not closely related) colonists to give myself a better start.

Answer 14

If you have artificial gestation, then the minimum vital number drops significantly, because you can run all viable crosses each generation. The potential number of offspring (of each gender, assuming one of each) in such a case, can be expressed as (f^m)*2, where f is the number of women and m is the number of men. For example, (3^3)*2 = 18 (9 girls, 9 boys). Granted, a population that low wouldn’t survive, since each generation 2 female genome would have only 4 potential non-cousin matches, and a generation 3 female would have none, as they would all be second cousins). Still, this method has the advantage of reaching viability much more quickly the more “new blood” is added.

Answer 15

I haven't read all of the answers above so if I repeat someone I apologize.

For anyone that has read hard sci-fi the question of epigenetics comes into play and the available equipment/technology/knowledge base aboard this vessel.

What are the genetic "trees" of the people involved, including any recessive diseases etc. Is there the capability of "altering" genomes to increase heterozygosity. What are the dictating scientific social mores at the time and in the location regarding these things? These all affect the answer of the minimum healthy population.

Are we sending genetic samples from other people with them to semi-artificially increase the heterozygosity of the population? The age of the people being sent up (i.e. years of viable gestations). It is much less resource and supply intensive to have the capability to transport supplies, organic or non-organic than people themselves.

How diverse is the information base of available information and the skill sets of the explores themselves? The more "jack of all trades" included with a few "specialists" would be more optimal than many specialists and a few multi-potentialities.

I think with near future technology the number could be under the previously mentioned 160. There would need to be more women than men, preferably younger and all people involved, even specialists would need to be able to be trained and educated in multiple variety of roles.

If the near future has viable artificial wombs then the need for more females than males would no longer be necessary other than the potential for it possibly being a lower likelihood of aggressive behaviour.

I would say with appropriate technology, supplies and ingenuity that as few as 75 genetically diverse people would be more than enough, very likely even less. IMHO

Answer 16

The answer to this is a ~40 based on the Sentinelese tribe(s) that are located on an island numbers vary from about 40 to 500 people as far as researchers can tell. This number is estimated based on what researchers can see from a distance due to researchers not being able to get on the island. The group has apparently been around for about 55,000 years and has had no contact with the modern world save for possibly at a distance, seeing planes and helicopters.

Answer 17

We are not yet a spacefaring civilization. The moon doesn't count so Mars will be ur first test. We are getting close to having an artificial womb that will change the preceding answers considerably. In such a case every aspect of the journey, setting up on the planet and starting biological life could be robotic.

Answer 18

With genetic editing and modification to circumvent problems with inbreeding it is now possible to give rise to a world with only 2 people. Adam and Eve is possible.