After watching this video I am left with this question.
The video ultimately claims that humans will not disappear, but doesn’t do a great job explaining why.
Correct me if I’m wrong, but for the (or a) population to be and remain stable, the total fertility rate needs to be equal to the global replacement rate (which recently was 2.3).
And since the total average fertility rate appears to be currently at this 2.3, any drop in the fertility rate in place A would have to be compensated with a rise in the fertility rate in place B (assuming that, at some point, we would like to stop population decline)?
I guess one way for a population to remain stable, while women are having fewer than 2.3 children, would be to have fewer men? If a population has 100 women and 10 men, each woman would only have to have on average (a bit more than) 1.1 child? (Which would of course also require a collective form of prenatal sex selection.)
I realize that would be bonkers and unethical. Just wondering out loud.
The replacement rate isn’t static. It depends on both how many people exist and how many people are having babies and how many babies they’re having. If the total number of babies per year stays constant, then whether it’s below or above the replacement rate depends on the size of the population. So for a hyper simplified example, if 100 babies are born per yer, that’s below replacement for a population of 110, but above replacement for a population of 90, but overall the population size will trend towards 100. Obviously real life is way more complicated, but even if the birth rate is low now, it’s far more likely we’re just moving towards a different population size, not a population of zero
Expressed as “the average number of babies that an individual woman needs to have for a certain population to stay the same size”, the replacement rate should not depend on population size, right?
If you express it as an absolute number (e.g. number of babies per year) than obviously it will depend on population size.
From what I understand, the replacement rate (expressed as the average number of babies that an individual woman needs to have for a certain population to stay the same size), depends mostly on what percentage of people die before they (can) have babies.