I understand that many women will not have kids or will have only one kid, or that child mortality is involved but still a fertility rate of 2 means that ON AVERAGE every woman will have 2 kids. This means that every woman and man will be replaced, including the children that die young if the rate of 2 lasts (the newborn females will also have on average two kids). So why isn’t a fertility rate of 2 enough to replace the population?
In: 701
Remember Timmy who got killed by running his motorbike too hard when he was 15, or Chloe that died at the hand of a hit and run?
That’s the .1
Even if every child born reaches maturity and have 2 offspring of their own, you will have a stagnant population. 1:1 parent:child does not allow for population growth. Having more children is ultimately necessary for continued population growth which under fiat style capitalism, is required.
If it was as simple as replacement, 2 would be fine. The population becomes static.
But imagine if something happens that kills a lot of people. Like, I don’t know, a pandemic.
The population won’t bounce back. It remains static. The lower number is forever.
A century later, another pandemic.
The population won’t bounce back. It remains static at the lower number.
And so on, and so forth. As long as the birth rate and the death rate match, disasters will steadily chip away at the population. In order to keep the population up and thriving, you need to have a slightly higher birth rate to account for these things.
If two people have two kids, population stays equal. And that’s assuming every child lives to adulthood, which they won’t. Two people having three kids increases the population.
Assume that the replacement rate considers women of child-bearing age. Then factor in the women who die before they actually have children. They were still of child-bearing age, so they through off the total count, but didn’t have kids, so reduce the replacement numbers. E.G. a woman, aged 55, dies childless. She was of childbearing age, but had no children. Another woman, also of child-bearing age, has to take up that slack.
Not everybody reproduces. Not everybody lives long enough to reproduce. Not everybody is able to reproduce. You have to make up for that difference.
Two reasons:
The first, which a lot of people have commented on, is because some people die before reaching reproductive age, thus the average acros all woman who have reached reproductive age needs to slightly greater than two to account for these early death.
The second, is because more more men are born than women. The natural ratio is 106 male births for every 100 female births. So for 1 million women to give birth to 1million girls they would need to have 2.06 million babies, or 2.06 births per women.
Combine those two factors gets you to 2.1
It is worth noting that sex selective abortion is bad enough in some places that it is up to 125 or so male births for every 100 female births.
Because not all children make it to reproductive age, or find a mate/reproduce once they get there.
If each woman only produced exactly 2 offspring, then on average there would not be enough to replace the previous generation AND compensate for the ones who fail to have children of their own.
Easy math is that in non-replicating species such as humans it takes production of two offspring to merely replace the parents in the grander population perspective. A third production is required to affect a positive population increase at the individual (or couple, really) level, and it’s subsequent generation surviving until they they themselves reproduce effectively (again, with 2 children being replacement, one or none having reductionist influence, and 3 or more contributing to an overall increase in population).
If two parents have two kids, then the population will stagnate. Remember, someone else’s kids share two kids, so in practice a grand parent would have two kids and share 4 grandkids.
Latest Answers