My model was only allowing for people 26-40 to "breed". I expanded it to reflect contemporary US breeding ages of 18-44, which helped.
TLDR:
Equilibrium Birth Rate: To maintain a population of ~100,000 (the baseline amount in this example) (±5%) over 100, 200, and 300 years:
100 Years: ~2.4 children per couple (final pop: 98,765)
200 Years: ~2.45 children per couple (final pop: 99,231)
300 Years: ~2.45 children per couple (final pop: 101,124)
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Equilibrium Birth Rates, revised for infant mortality and variable mortality:
100 Years: ~2.55 children per couple (final pop: 99,876)
200 Years: ~2.60 children per couple (final pop: 100,342)
300 Years: ~2.60 children per couple (final pop: 101,567)
Explanation
Impact of New Factors:
Infant Mortality: Reduces births by 0.56%, slightly increasing the required birth rate.
Variable Mortality: Higher mortality in older age groups (60+) shifts the age distribution younger, requiring a slightly higher birth rate to compensate for faster elderly population decline.
=========================
So 2.6 seems to be the magic number for long term stability of a population WITHOUT the need for migration, and barring any (((wars))).
I have 3 so I guess I've done my part. Everyone else needs to get fucking.
My model was only allowing for people 26-40 to "breed". I expanded it to reflect contemporary US breeding ages of 18-44, which helped.
TLDR: Equilibrium Birth Rate: To maintain a population of ~100,000 (the baseline amount in this example) (±5%) over 100, 200, and 300 years:
100 Years: ~2.4 children per couple (final pop: 98,765)
200 Years: ~2.45 children per couple (final pop: 99,231)
300 Years: ~2.45 children per couple (final pop: 101,124)
=========================
Equilibrium Birth Rates, revised for infant mortality and variable mortality:
100 Years: ~2.55 children per couple (final pop: 99,876)
200 Years: ~2.60 children per couple (final pop: 100,342)
300 Years: ~2.60 children per couple (final pop: 101,567)
Explanation Impact of New Factors: Infant Mortality: Reduces births by 0.56%, slightly increasing the required birth rate. Variable Mortality: Higher mortality in older age groups (60+) shifts the age distribution younger, requiring a slightly higher birth rate to compensate for faster elderly population decline.
=========================
So 2.6 seems to be the magic number for long term stability of a population WITHOUT the need for migration, and barring any (((wars))).
I have 3 so I guess I've done my part. Everyone else needs to get fucking.