1) is life expectancy. Suppose the average life expectancy is 40, and every two people have two children at age 20. Population would be stable. However, suppose nothing changes about fertility rates or replacement rates, but the life expectancy grows to say 60. You'll find that the population for some time will grow, merely because inflow (births) don't change, but outflow (deaths) are lower as they are delayed.
As such, population growth can occur despite a below-replacement rate fertility without any immigration.
2) Immigrants tend to be more fertile. Welcoming immigrants and then chalking up the subsequent population growth from their high-birth rate as being an example of the country having sufficiently high birth rates for population growth without immigration is faulty reasoning. Births in the US would've been a lot lower if it admitted no immigrants, particularly hispanic.
Fact is total fertility rates in the US are around 1.7 children per woman now, and are even lower for people who's families have been in the US for multiple generations (non-recent immigrants). US would be declining in population size this century if it wasn't for migration, ceteris paribus.
Similar story all over Europe. Just look at fertility rates of native-born populations and the necessary replacement rate, the former is typically below the latter. [0] Most OECD countries would be shrinking without immigration.
1) is life expectancy. Suppose the average life expectancy is 40, and every two people have two children at age 20. Population would be stable. However, suppose nothing changes about fertility rates or replacement rates, but the life expectancy grows to say 60. You'll find that the population for some time will grow, merely because inflow (births) don't change, but outflow (deaths) are lower as they are delayed.
As such, population growth can occur despite a below-replacement rate fertility without any immigration.
2) Immigrants tend to be more fertile. Welcoming immigrants and then chalking up the subsequent population growth from their high-birth rate as being an example of the country having sufficiently high birth rates for population growth without immigration is faulty reasoning. Births in the US would've been a lot lower if it admitted no immigrants, particularly hispanic.
Fact is total fertility rates in the US are around 1.7 children per woman now, and are even lower for people who's families have been in the US for multiple generations (non-recent immigrants). US would be declining in population size this century if it wasn't for migration, ceteris paribus.
Similar story all over Europe. Just look at fertility rates of native-born populations and the necessary replacement rate, the former is typically below the latter. [0] Most OECD countries would be shrinking without immigration.
[0] https://en.wikipedia.org/wiki/Total_fertility_rate