What is a realistic growth rate for a space colony?

Question

I am starting a theorycrafting thread in a video game forum. It deals with the creation of a Hegemony created by the descendants of a colony ship that was cut off from returning to Earth (wormhole collapse) and needed to establish themselves in a new part of space.

Link to the thread found here: Artemis Theory: The Artemisian Hegemony

What would be an appropriate growth rate for a space-faring civilization given the following parameters:

1. Nearly fully functioning/intact colony ship upon arrival at destination (85%-90% intact) containing all necessary equipment and supplies to establish a colony
2. Unable to re-establish contact with Earth or other Earth Colonies;
3. Tech level: Space-faring (no warp/ftl capability but ships can travel at 0.1 c), maintain level of technology consistent with humans in the year 2232 in regards to medicine, agriculture, research, manufacturing and processing.
4. Time period for growth: Approximately 600 years
5. Encountered Predatory Species, Diseases, Social Unrest: Low to moderate chances. Colony would have been cut off so probably would have taken an isolationst stance; excellent medical preparation should keep disesase rates to average or below average; Due to nature of location colonists would have kept civil unrest to a low to moderately low state.
6. Starting population 5,000 people (sorry I knew I forgot something important)

Thank you in advance

Answer 1

I don't think they'll retain their space faring technology for long. Modern space-tech is so complex there are only a few industrialized nations on Earth capable of doing it. Your population of 5000 simply won't be able to produce the raw materials, nor be able to maintain the high tech tooling required to maintain and repair their high-tech tooling.

Pick any modern convenience. Like a microwave oven. After a few years, it'll break. What do you need to build a new one? A magnatron, a flyback transformer, metal and glass plates, electrical components. What do you need to produce those? Fine tools, metalwork and glass for the magnetron. Vacuum pump. Fine, high purity copper wire for the transformer, iron, steel. This requires mines, ore smelting, purification. Fabrication facilities. Smelters and kilns. What do you need to make all those? What tools do you need to make those tools?

So stuff will break, and the tools to repair things will break, all the machines the colony starts with will break, they will run out of duct tape. How do you make new duct tape? And so the society will slowly slide backwards until an equilibrium is reached with what they can reasonably produce and sustain themselves. Sustainability is the key thing here, anything the colonists bring with them won't last long, only the things they can constantly produce themselves will matter after a few generations.

Where is that equilibrium point for a society of a few thousand? Probably living in mud or stone huts, dressed in animal skins, using tools made from bones and pointy rocks, malnourished, hunting animals or working 18 hours a day in an iron mine, and dying at 30.

The modern society tech tree is extremely large with massive inter-dependencies. It takes a population of hundreds of thousands, maybe millions, before it becomes economically viable to produce things like industrial weaving machines and internal combustion engines. In a resource and food rich land (best case scenario) your colonists would need to focus on survival and breeding, and over many generations increase the population to millions before there is time over so they can start to support specialized professionals like metalurgists or chemists or electrical engineers, which is when technology really starts to take off. Until then its just a very, very long slog through the mud (a few tens of thousands of years if our own civilization is anything to go by).

Answer 2

I think that the fact you stated that it is a "colony ship" auto-negates the "omg! Decay to the stone age in ten years!" scenario. A COLONY ship would be equipped to establish a COLONY. That means it wouldn't be packed with the 23rd century version of ignorant valley girls and frat boys. Look at the training modern astronauts have to go through just to float above earth for a bit and maybe spacewalk. I'd wager that a colonist would be a mid-late 20s fertile individual who, regardless of sexual orientation, aggrees to participate in manual population growth until fertilization clinics can be established AND has completed the equivalent of a doctoral course including:

Survival, Psychological toughening, Technological interrelated history (like the old tv show "Connections" but on a much deeper level), Staggered specialization (medical, mechanics, applied sciences, etc. And each colonist would have a primary specialty), Overlapping familiarity with several other specialties.

Likewise, the colonization process would be planned, not improvised:

The colony ship would probably be designed to at the very least be cannibalized for shelters and machinery construction, if not designed to permanently land and become a small city/fortress at the colony's core once scout craft found its landing site. The ship's reactor would become the planet's first power plant. Engines vecome turbines to generate additional power or perform rapid excavation. Birthing becomes sheltered lodging. Hydroponics is now a giant greenhouse with preestablished familiar flora. Medical bay is an instant hospital . . . you get the idea.

After initial food, shelter, and safety are started, the very next project would be population control. Long before they boarded, each colonist should have a paired mate, and the couple assigned a place in rotation for reproduction. Especially once they know they have been cut off from emigrants/reinforcements, breeding becomes a matter of the group's survival, and would be kept as a priority at least through the first generation.

Your 5000 arrivals would likely close to double their number (each couple having roughly 4 children in a span of 10-15 years of remaining fertility is not unreasonable if it is a focus of the group as a whole). After that, population would still probably be at least that of 19th century England. Another part of that preparedness would probably include the medical knowledge of now+200 years having packed along some rather reliable fertility treatments.

Add to that the fact that your colonists could easily have the knowledge (or have come up with it in another 600 years) to create cloning facilities and artificial wombs . . .the 12 million estimate is conservative. You could just about make them have spread to numerous sub-colonies by now, and could number in the 10s or even hundreds of millions.

Answer 3

There's 2 factors you need to consider:

1) What are the resource limitations of your colonies? On Earth humans have basically reached the point where carrying capacity doesn't really apply in the short term (long term problems like global warming are still an unknown, but I suspect modern technology will be enough to prevent a population collapse). In space you need to worry about rationing spaceships and food, which really comes down to the initial colonies industrial base (aka, how quickly they can build more colonies). Here there's really no theoretical limit, as most of the factories will be automated at that point. Plus on earth like planets there's not even those constraints. Ultimately it's just a matter of how much they prioritize making new colonies vs, say, making barbecues, toys, and space cars.

The only big limiting factor is growth will have to stop during interstellar travel (maybe they freeze everybody), but when they arrive exponential growth can continue. This travel time delay would basically be just that, travel time, nothing more (assuming they start near the middle of the galaxy, crossing it would take 50 million years ish, but that's an engine problem, not a population one).

2) The real limiting factor for a modern society is the number of children people choose to have. In much of the rich world population is going down because women (and men) would rather focus on education and careers than having children. Presumably an advance space faring society would face a similar issue, and could possibly never even expand beyond their colony. Niger has the world's highest fertility rates at the moment at 7.6 births per woman. With that kind of growth, and a society focused entirely on expansion, then you could have a population be ~1000x larger every century, continuing exponentially. However, this is unlikely as they probably wouldn't want to have that many kids. Really it depends on their society though, is this 40k or Star Trek?

Answer 4

Peaceful scenario: 600 000.

Action scenario: 12 million.

Modern history shows that birth rates decline towards replacement level when things are going well. Picking a typical post-war western growth rate of 0.8 percentage per year, we get 600 000 people from a starting population of 5000.

A more interesting scenario is where there is something causing people to have more children, in the face of good or at least increasing levels of health care. The population of England grew from 8.3 to 30.5 million people between 1801 and 1901, giving a growth rate of 1.3 percentage per year. That is: 8.3 * (1 + 0.01309)^100 = 30.5

If we apply the same growth rate to your scenario, we get 12 million in 600 years.

Answer 5

Too many variables, I'd say: 250.000 citizens

There's no telling how human technology will evolve in the next 200+ years. We went from the first mass produced car (Ford Model-T) to walking on the moon in 60 years. Many jobs will get automated over the next 50-100 years, robots already fill our factories, and as time passes they will become more and more sophisticated. I don't think that, as state in other answers, resources will be a major hindrance.

Usually a colony ship doesn't return to earth, and you don't start a colony if you can't provide it with resources or the knowledge to acquire them independently on its destination planet. Especially since interstellar communication is almost like time travel (very difficult to achieve effectively), a colony will need to be self sufficient right from the start.

In the end, as stated above, there are too many variables for me to give an educated answer. But...

I'd say, since it seems a pretty nice planet they found and 600 years are more or less 24 generations, that there could be more or less 250.000 people living there after that time period. This means that every colonist will have at least 2 children by the age of 25, which will then have 2 children on their own, and so on...

BTW, if your colony starts with only 5000 people, and will never get immigrants from earth, then you will get gene pool issues after a while.

Answer 6

Considering the comments about a colony degrading technology wise, I would use the growth rate of the New England Colonies. Wikipedia gives the rate of 3% per year for births, and 1% per year from new emigrants.

Having women bear children, for the sake of the colony, probably won't 'sell'. But if the space colony was like our American colonies where your retirement plan was having enough children to support you in your old age, then having children is very important.

Although having a child takes a woman out of the workforce, for a while, the workforce will be dominated by low skilled, manual labor for several generations. Expect to see men and women working on the farm with babies on their back.

Preschool and Kindergarten will be replaced with chores and growing responsibilities. Children will have to work the farm and help their parents with some cottage industry after dark. When the colony grows to the point to support factories, expect children to be there too.

https://en.wikipedia.org/wiki/Demographic_history_of_the_United_States#Earlier_Colonial_era

Answer 7

Starting population of 5000 - I will assume 2.500 males and 2500 females, all heterosexual and under 30 years old.

A woman can have one child per year - so in theory your 2500 couples, can have one child every year.

I will assume that in first year, no children will be born - colonist will be focused on setting up the colony and obtaining constant supply of food and water.

From second year on, after colony is stable, we can assume that most couples will try to have a child (lets say one, ignoring twins). Since not all attempts will be successful (natural births only, no extra medical assistance), we can assume 1000 newborns out of 2500 possible. That's 20% increase by the 3rd year (at minimum).

After that, it depends on your society. If you keep similar to modern western societies, the original couples will stick to 1 or 2 children on average. If you have them simulate old America colonization, or even medieval Europe, then each couple can have 5 to 9 (or more) children - these societies depended on new children for growth (not to mention that there was no tv or internet then).

Also, as your colony grows, so must your food production and water supply.

I think for a starting colony 2-4 children per couple will be acceptable. This rate will drop to 1-3 for second/third generation settlers.

With that in mind you will have an estimated average population growth of 30%-40% for your first generation colonists.