By how much would a human population of say 2,000 grow in 100 years?

The situation is that 2,000 odd humans are stranded on an vastly inhabited planet (In the future) without contact back to Earth for at least 100 years. A few scenarios I have considered in the growth of population are...

1. The rapid loss of useable technology (what was taken over from Earth) due to lack of power

2. survival on a new planet - considering unknown dangers like predators and diseases, along with the hunt for food, warmth etc

3. Lack of medical supplies (not doctors, there would have been scientists etc within the original 2000 population) - so considering that many women may die in childbirth

4. Natural infertility - not every single woman will have two children (but some may have three or four)

5. human violence - Undoubtedly over one hundred years there must inevitably be fights and squabbles over food or shelter.

With all these considerations (please mention if I have missed any other important ones worth considering), I have come to a population from 2,000 to about 11,000 within one hundred years with some simple maths and calculations of reducing factors. Does this sound realistic given the humans are on a completely different planet without technology in the future?

Perhaps humans have come too far with technology to ever fully adapt and survive elsewhere without it, or may be our instincts will very quickly re-surface and after the first few years of getting used to it would start to re-build itself.

• Can you show some of your calculations? It's not necessary here; I'm just curious as to your methods. Commented Sep 6, 2015 at 18:10
• Did you consider the loss of contraception ? (which could be included in "lack of medical supplies") Commented Sep 6, 2015 at 18:21
• Sure, the method I did was very crude and cant consider all factors but its along these lines: Assume half the population are female and all have two children (safe number for now), then already there is an increase of 4,000, then in twenty or so years, with half of them being female they also have two children each etc etc. I say two children because some may have none and some may have five, so its seems a neutral number to choose. Then when I get to about 15-20,000 over 100 years I shall then put the reducing factors in and cut the population down :) I'm not great at maths I'm afraid ;) Commented Sep 6, 2015 at 18:26
• @Kolaru Thats true, I had not thought of this! I guess that would increase the birth rate higher than the current one quite drastically, BUT also may not have an effect on it due to birth related deaths levelling it off again - I think it would be a tricky calculation to find out which one of those factors has the biggest impact on long-term population. Thanks for your help c: Commented Sep 6, 2015 at 18:47
• All of the figures being quoted seem to assume that the only limitation on the population size is the birth rate. Surely the main limiting factor is the ability of these survivors to feed themselves. How many of the 2,000 have agricultural experience? How many have agricultural experience in an alien environment? I'd imagine that for the first 10-15 years they would simply be fighting for their own survival. Doubling the population early on would put a great strain on that ability (as well as reducing the number of people available for manual labor). Commented Sep 6, 2015 at 19:56

The highest population growth rate in the world at the moment is around 3% per year. This seems a reasonable starting point for you since you will have both negative and positive influences.

This would give you a population after 100 years using a compound interest calculator of 38,437.

In other words 11,000 is not just achievable but if anything low. This difference could easily be explained by the harshness of adjusting to the new environment though.

• Yes I was also getting a figure of over 30,000 when doing a simple calculation, but cut it down drastically by considering all the 'new' scenarios which may occur when on a new unknown planet. My major cut-downs were such things like: birth-deaths, starvation (within the first ten years anyway surely must cut the population by almost half?), and predation. Perhaps I was over estimating how many deaths there would be, may be boosting it up to something like 20,000 would be more realistic perhaps. Commented Sep 6, 2015 at 18:35
• @Sezaii You have to remember that people also increase birth rates to compensate. Consider for example the difference between Afghanistan and the United Kingdom in terms of infant mortality, life expectancy, etc. Then realize that the UK actually has a lower growth rate and most of that is due to immigration... Commented Sep 6, 2015 at 19:02

I know this is an old post but as I have a similar issue to calculate, so I thought I would put my two cents in. Did you take into account the loss/retention of medical (and other) knowledge into account?

For instance the first generation or two will still have 'modern' or ' future' day medical knowledge even if they do run out of medical supplies/technology. So at first there could be a slighter higher birth and survival rate than expected! This knowledge can then be lost over succeeding generations resulting in a decrease in birth and survival rates back to say 19th century Industrial Revolution equivalent and then even worsening to Medieval growth rates if you are particularly vindictive to your population.

Assuming that women accept their lot as broodmares for the survival of the community; You could work on the fact that women can survive an estimated 3 births (using similar reasons you used for 2) for a generation or two. Giving you a starting population of, um...hang on.

If you have a starting population of 2000 and assuming equal male to female ratio like you have you get 1000 a piece! You then have to take into account any older women or younger children who are not of child bearing age! Physically not possible! So for arguments sake you cut it 50/50 again, so you have roughly 250 old people, 250 kids and you get 500 women of childbearing age who have roughly 3 kids each over their lifespan. That's 1500 in the first generation (not taking into account any multiple births - apparently there are 32 twin sets per 1000 births).

For the second generation: You have two scenarios. If your starting population was mostly adults to start with you would have a large age gap between your first and second generation with a potentially large loss of knowledge etc occurring. If you had a normal demographic of young, adult and older people in your starting population you would have a more even retention of knowledge over time.

I'm using the even demographic scenario here for generation 2. These would be the ~250 kids who were born off planet and presumably had a good start in life health wise. So they would be robust, maybe having some medical procedures at birth making them more healthy than those born on planet. Let's be generous and say they get the 3 to 2 birth rate mentioned above. So 250/2 (male to female ratio) = 125 grown teenagers/20 something's ready for childbirth around 10-15 years after landing. That's roughly 250-375 more babies bums to wipe. Let's say 300 for the sake of easy numbers.

The third generation would be the children of your 1500 initial births. So, 1500/2 = 750 girls reading for childbirth 15-25 years after landing. Unfortunately for them, they have a higher chance of all those childbearing issues mentioned above so say only get the rate of 2 births per female. 750*2= back to 1500.

So after 25 years, you have gained: an initial population of 2000 First generation born on planet of ~1500 (fairly healthy infants - benefits of pre landing technology and tech) Second generation born on planet ~300 (fairly healthy infants - benefits of pre landing knowledge and maybe some tech) Third generation born on planet of ~1500 (starting to increase infant mortality - no to little pre landing tech and starting to lose knowledge)

That's 5300 people not including any losses, and that is optimistic! Let's say a third die to disease/predators/conflict/human stupidity. That's only ~3500 in 25 years. That's a fairly high growth rate of 1.75% (between 1950-2000AD we had a growth rate of 1.7%). It's from here that you could possibly have a level or downward rate to calculate your population over the next 75 years.

This older similar question may help especially the first answer with growth rates provided by the Real Population Problem

Factoring in the knowledge base of where your population comes from and the loss of tech and supplies I think we could adequately place them in the 1870 - 1950 AD era for the majority of the 100 years but for the first 25 I would say use the 1950 - 2000 AD growth rate (which pretty much lines up with my calculation above!)

•25 years at 1950 AD to 2000 AD rate of growth at 1.7%: 2000×1.017^25≈3048.

•75 years at 1870 AD to 1950 AD rate of growth at 0.82%: 3048×1.0082^75≈5623 people after 100 years.

This is against just using one growth rate of 0.82%, which results in just over double the starting population of 4525 people in 100 years. And remember, you won't have any incoming migration to boost your population numbers, it will be a closed system. So, in fact it looks like you were over estimating!

Obviously you can play around with the population growth rates depending on how hard a life you want to give your stranded victims.

• why so complex, why just not take historical data like that and go with them. Commented Jun 19, 2016 at 19:34
• or something simple like that in one of A of Q you have mention Commented Jun 19, 2016 at 19:47
• @MolbOrg I actually only found the graph for the last 5000 years after I had done comment. And most of the A of the 900 years Q that I linked where using huge numbers that I thought where a bit unrealistic in this situation. What I wanted to show was that each generation builds from the past or loses from the past. If you had a space going civilisation stranded, you wouldn't immediately start with a 1000AD population growth rate. There would be decline from their starting population rate that they had been at before they levelled out as they settled into the situation. Does that make sense? Commented Jun 19, 2016 at 21:11
• Small or big number does not matter, math matters. I'm ok with your answer, people are different and it may be very helpful for someone. First part of your A is simulation trough description by words. Everything is simply - they extinct in time from 5 min to 10000 years or they prosper and grow. There is only 2 q to answer how fast they may potentially grow and how long may take extinction. So you do not need graph from beginning of time - not extinction means grow at 0% to highest number we have seen 3+%. Big number are ok thats exponent - if opportunity is given we may inhabit universe fast. Commented Jun 19, 2016 at 22:17
• 3rd generation born after only 25 years? How can the first generation born be grandparents at 24? Commented Jun 20, 2016 at 9:05

Just for fun consider that this population has technology exceeding our current technology and that the colonists were initially six women for each man with the intent of growing the colony as fast as possible. They would have brought no disease with them to that new world. The new world would have been tested as disease free before building the colony there. All of the colonists would have been tested as extremely healthy and fertile with the first generation having six children per female, but gradually leveling off where the men and women are equal in number but still intent on having as many children as health allowed. No one has any genetic problems. Ages initially would be between 20 and 30. Unlimited food, shelter, and electrical power with a stock of seed and animal embryos as well as edible wild plants and animals and a very benign climate. The colony would have highly skilled doctors who would continue training new doctors and the equipment to synthesize replacement medicine. They would have arrived with machine shops, farming equipment, etc. and the knowledge to mine and refine ore and build factories. See my "Ancient Destiny" series of books where the initial colonists on this virgin world actually number 50,000 or more as the result of a mass exodus from Earth. My grandmother, an early pioneer in Oklahoma, had 9 healthy children without doctors available. Kept wanting more boys to help farm. The first was a boy followed by 8 girls who helped farm plowing fields, etc. The average American couple today has 2.4 children and they don't need children to deliberately increase the number of people. If they were farmers farming by hand the number of children would again be very high. If a woman does not average two children, the population will actually diminish in that country which is why Europe needs immigrants to work the factories. search for "ancient destiny by albert clark"

• Welcome to WorldBuilding.SE! First of all, please break this up into paragraphs to make it easier to read. It's currently an unreadable wall of text, and it's hard to tell how well it answers the question. I will thank you, however, for disclosing that you are the author of the book you cited; if you didn't, this might have been deleted as spam. Commented Feb 21, 2019 at 21:21

For fun (well, a kind of :) ), I've tried to make a spreadsheet estimate of population growth. My figures brought to a figure of about 12k people after 100 years, so your numbers seem fully logical.

What I did (very difficult to explain without showing the actual spreadsheet):
* I subdivided the population into 3-years ranges, starting from 0-2 yrs up to 81-83 yrs; for every range, I speculated a numer of colonist: from 13 colonist, for the older ranges, up to 130-150 colonists on the higher fertility ranges (20s and 30s), and 60-70 colonist for every under 20 range, so that the total number of colonists is 2000; so every row of the excel is a range of age
* Every column of the Excel is a 3-years period of time (so, year 0, year 3, year 6...)
* I created a formula to populate every cell (= estimate the population of every age range at every 3 years milestone): for every cell in the column, the population of a range equals the population of the previous range in the previous column, multiplied for the percentage of survival (I took a rough estimate from World Health Organization tables, but anyway it is in the order of 99-98% for the infant and adult ages); for instance, if in the year 30 I have 100 people aged 30-32, in the year 33 I will have 99 people aged 33-35
* In the cell of the 0-2 years I placed the number of new born in the 3 years period; my formula is 95% of half of the 21-23 age range (half because estimate half females and half males), 85% of half of 24-26, 75% of 27-29 ... down to 15% of the couples 39-41. Rather than estimating the effective age at which a baby is born, this formula tries to estimate how many sons a couple will have in its life: for instance, 15% of the couples will have 7 sons or 75% will have 3 or more sons... I speculated a higher-than-average fertility.

By extending this calculations up to the year 99, I found a population of 12433 (2000 of whom aged 0-5...), which is fully coherent with your estimate.
But varying the age composition of the starting sample of colonist, the estimations of the number of son/couple or the mortality for range of ages, I can find very varying values (either higher or lower).
Of course I should have considered also an increase in mortality beacuse of loss of knowledge and medicinals, but I think it would affect more the mortality in the older population, so it would have a small effect on the increase of population itself.