In relation to my other questions, the earth gets destroyed in 2165 and the humans that would have survived go to a new planet.

Now, context is that the humans have been into interstellar travel for about 80-90 years after their warp development and before the planet's demise. So, in that time they have founded a few colonies with a few thousand colonists (mining and agriculture), They'd have already established a new planet as their main colony planet with about 50,000 -70,000 colonists before the earth-death.

Now, with two weeks warning, the humans and their alien allies start to evacuate earth.

The population of the earth at the time would be about 10 billion (to why they set up other colonies, overpopulation was a major factor) and would significantly drop (this low-key makes me wonder if humans would be classed as an endangered species) My thoughts would be that approximately 19 million would be saved at this time. Full ships are carted off to the new homeworld and returned for the next lot.

After the planet is gone, survivors are taken to the new homeworld and allied worlds. There they'd all be registered for a head-count of survivors and assigned supplies while they deal with the mess. Since humans are quite advanced and would rely heavily on their alien allies for aid, they'd have access to medical supplies, emergency homes and advanced technological equipment.

Abortions would be illegalised (but it's possible to transfer the child into an artificial womb after a certain time of original gestation) and care for infants would be considerably higher. Most people would be expected to donate their genetics to a genetic medical facility; to keep more genetic material available for later down the line.

So, 200 years later, the human population would have grown and they would be back on their feet. But I'm not sure what sort of figures I'll be looking at in terms of an approximation of the human population in that time.

I suck at maths so I hope the numbers I have are reasonable.

So, What would the approximate human population be in 2365?

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    $\begingroup$ This depends crucially on how much infrastructure and support humanity has (from both their colonies and the friendly aliens). With 20 million people crammed into colonies that were formerly supporting a few hundred thousand people, total, the question isn't how to have enough kids but how to feed, house, and clothe people - even just the people you have right now, let alone children. $\endgroup$ – Cadence Jul 3 at 11:00
  • $\begingroup$ Are there any Government Incentives programs to increase birth rates? Should we take "average" human population growth, Baby Boomers growth rate, or "medically induced octuplets" growth rates? How are you counting hybrids (offspring of human + other)? $\endgroup$ – Michael Kutz Jul 3 at 11:07
  • $\begingroup$ There would be a basis of a government that maintains the colony, each one would have slight differences based on their original culture but each colony would answer to someone, possibly the equivalent of the president. With the mass of people introduced, it takes several decades for things to settle down so at first, it's average at first, including death as a result of crime rates, accidents and natural causes. The second half of the first century would have a baby boom (no medical induced more than two by willing females) Hybrids aren't yet part of the equation here. @MichaelKutz $\endgroup$ – SKKennell Jul 3 at 11:27
  • $\begingroup$ Birth rates depend upon many cultural and policy factors that are not defined in the Question, and seem likely to change over 200 years. Folks tend to have more children when they can afford to, when children's mortality is high, when children's support is required for eldercare, when women have little power, and other various factors. $\endgroup$ – user535733 Jul 3 at 11:55
  • $\begingroup$ How soon into pregnancy could the embryos be transferred to the artificial wombs? $\endgroup$ – Wiggo the Wookie Jul 3 at 12:54

Current avarage human population grouth is about 1% per year, wich doubling every 70 years.

By this condition your population would be around 20 000 000 * (1,01)^200 = 146 000 000 (almost like Russia)

If you put all efforts in ... breeding, you could get up to 5 grown up children per family. To many children per grownup leads to lack of control and care. And this greatly encreases probability of different accidents. So even if family on average "produce" 10 children (this is a lot - it means that a lot of families has about 20 children) 2-3-5 of them would die before marrige (on avarage).

Since one "production cycle" is about 40 years (your need time born all them) it gives doubling population every 8 years. In 200 years there would be 25 doublings and total increase factor would be 33 554 432 times, thus given total population of 600*10^12 wich is like total humanity (or maybe Orcs?) from WH40K

So this is you "working interval" where you can take any number you want for your narration: from Russia (140 millions) to WH40k (600 trillions). Anything between is possible in appropriate conditions.

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Human populations can easily double in 30 years in good conditions absent any new technology. 200 years is roughly 7 doublings, so you would expect to have 128 times as many as you started. Your 19 million would have grown to roughly two and a half billion.

Some individual countries are currently growing much faster, eg Southern Sudan with a growth rate of over 3.5%. Compounding this over 200 years = a factor of 972 so 19 million is now 18 billion.

However, given SF technology you might expect very much more rapid growth if there was a cultural/political will and the economy to support it -- make all children female and parthenogenic and with multiple births being the norm rather than exceptions. Population could easily be 180 billion or more...

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I would start from @Cadence 's comment to the question:

With 20 million people crammed into colonies that were formerly supporting a few hundred thousand people, total, the question isn't how to have enough kids but how to feed, house, and clothe people - even just the people you have right now, let alone children.

So, unless the friendly aliens are willing to help without limitations and without strings attached (but why would they do that, especially considering how dangerous we, as a species, are ?), increasing population will not be the most important issue until the infrastructure to sustain a 20 million population is built and surpassed.

Second, what kind of people are those 20 million ? The rich, who can buy their way into the fleeing spaceships ? The yound and healthy, who can do physical work and reproduce (and fight their way into the ships if necessary) ? The old and wise, who know technology and skills ? Or, of course, a mix of those ? (Who gets do decide ? The already established colony, the aliens, the Earthbound establishment ?)

If this imported population is not young enough, it won't reproduce or build new facilities as fast, but it will probably help in planning the future and preserving important Earthan technology and general lore. If it is very young, it will reproduce and help building things more, but it can be a threat of itself, either due to ignorance, entitlement, or turbulence. If it is skewed to the upper classes, it might prompt conflict with the pre-apocaliptical colonial establishment. If not, it might become an underclass and pose another, more radical, threat to that establishment.

Plus: how is this selected ? Are they all Americans, or Anglospherans in general ? If not, how many different languages do they speak ? How comfortable are they with cultural meltpots ? What are their reproductive habits (I take in 2165, they will mostly be used to having few children, and to be sexually free, including from reproductive collateral effects of sex) ?

All of those issues might have a much bigger impact than mere mathematics... so chose any figure you wish, but be prepared to discuss how that figure was arrived at, including:

  • The Rebellion Against Sexual Laws

  • The Great Reproductive Strike

  • The African Revolution

  • The Alien Withdrawal

  • The Advent of the Theocracy

  • The Reintroduction of Slavery

  • The War among the Languages


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