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Realistic Demographics - Proportional Pop Growth

NOTE: The 2.2.5 update shifted the pop growth values pretty much in line with those in this mod. I have been fairly happy with 2.2.5 growth rates, and with extensive testing I have not found an appreciably different result. However, I have updated the mod with some tweaked values (largely lowering influence of certain traits) due to popular demand.


This is a simple mod to change pop growth so it is more proportionally realistic.

It is NOT intended to prevent diverse civilisations or long-term changes in demographic balance. The game already provides many options for being xenophobic (no migration treaties, species rights, etc) and/or horrifically, fanatically xenophobic (genocide, being generally monstrous, etc).

Savegame compatible, but best results with restart.

Remember to think in RP terms!
- If your main species is slowbreeding, sedentary, and nonadaptive. And you intend to have migration treaties with fastbreeding, nomadic, adaptive. And they have the same planet preference. And you want to use no migration or pop controls. Then expect in the long run (100s of years, but depends on your existing pop numbers etc) that on new colonies they will outbreed the starting species. The ratio will shift slowly, though.
- Remember! Pop growth in ANOTHER empire can flow into YOURS, even if it is very sedate in your own. Overflow from other civilisations is more an AI problem than weighting one.
- If you want to keep some species EXCLUSIVELY on some planets, then use migration controls.

PLEASE NOTE: If you notice anything anomalous or odd or apparently bugged, please report it in the thread in the discussions tab of this page, providing as much exact information as possible.

Major rebalance:
The latest update has majorly adjusted the weighting to solve the problems of runaway exponential growth of species with growth/migration traits and/or slight numerical superiority. See changelog for details and number.

Examples:
Species A is a slowbreeding, sedentary species.
Species B is a fastbreeding, nomadic species.
Species C is a species with no growth-related traits.

With equal starting numbers, and all else being equal:
At 80 habitability for A vs 40 for B, A will fairly rapidly outbreed B (some B pops will grow at the start, but then stop).
At 40 habitability for A vs 80 for B, B will extremely rapidly outbreed A (very few A pops will grow).
At equal habitability, B will gradually outbreed A (after a few hundred years the ratio will be skewed maybe 3A:2B).
At equal habitability where both have the same homeworld, B will extremely gradually outbreed A.
At equal habitability where A has homeworld bonus weight and B does not, this is hard to test, but if numbers were equal to start then it would be close at the beginning, but A would eventually win out. If A already has numerical superiority they will maintain vast numerical superiority (although if they game ran for thousands of years who knows).

Introduced by migration treaty later on:
C will rarely migrate to worlds where it has 40% habitability.
At equal habitability C will never come to have a large pop-proportion on worlds with large numbers of A and B.
At equal habitability C will tend to be in the middle of numbers on new colonies.

External migration, refugees, and other sudden pop shifts will skew these demographics.
All of these numbers are also variable depending on growth techs, growth rates on different planets (and so internal migration).

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