Why isnt it just 2? What factors make up the 0.1?
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> Why isnt it just 2? What factors make up the 0.1?
It takes two people to have a baby. Specifically it requires a man and a woman… anyway, I don’t think this is the time for that talk. So everyone who has children needs to make 2 children to keep the chain going.
However, sometimes people don’t have children. They might just not ever decide to do so, or they might die, or they might be infertile or sterile, etc. Whatever the reason some people won’t have offspring and those that *do* have offspring will need to make up that slack to keep the population stable. On average that is generally understood to be the 0.1 births.
.1 is to make up for deaths.
So 2 replicates the mother and father, and .1 hedges against deaths that take place in children, those who are sterile, etc.
If you want to grow your population, 3 is a better number. There’s more losses than .1 covers for sustainability.
Just under half the population born is female. If every woman has two children, then a population would be sustained. However, not every woman survives to have children, and not every woman chooses to have children. Therefore, the number of births required to sustain a population has to be higher than two, and 0.1 just happens to be a reasonable increase to sustain most populations with low amounts of child mortality.
That’s not to say 2.1 births per woman would sustain all population levels. If an area has higher child mortality rates, for example, then more people would die before reaching reproductive age, requiring the surviving women to bear more children to sustain the population.
Takes 2 people to make a baby.
1 baby to replace the dad. 1 baby to replace the mom, .1 is making more.
Not every one person can have 1 child each due to a variety of reasons. Some of them include Death/ sterility/ buttuglyhood/ not wanting to have children/ alien invasion/ joing a cult/ etc.
Everyone is right that women who die will already be counted among the ones who will have no children.
The real reason is that slightly more men than women are born.
I am amazed that out of everybody commenting, nobody has managed to properly address the issue.
2.1 is the number necessary as a “prospective” metric. Technically, an average of 2 would equate to equilibrium, but that does not factor in those of the coming generation that will be sterile or die at young age etc. If all 4.x billion women on earth each had two twins coming out today and then the people currently alive would all magically vanish, we would have a sustained rate. But the correct frame of reference is not earth today but rather earth + 20 years.
Sometimes kids die before making it to reproductive age. It’s a sad truth but that’s why you need a little above 2 kids per couple in order to guarantee you can replace the current population and then some. To give concrete numbers, last year in the US 3.6 million babies were born. However, 37,000 children below the age of 18 died, or 1% of the number of children born.
Not every kid makes it to adulthood or has children of their own. You need the extra 0.1 to make up for the 5% of kids that die or never reproduce.
If everyone only had 1 child, then that would only replace 1 of the parents, meaning by the time the parents passed, the population would have a net decrease of 1. If everyone had 3 children, that would replace the parents and leave one extra, meaning when the parents passed, the population would have a net growth of 1. If everyone has 2 children, that would perfectly replace the parents. When the parents pass, the net change on population would be 0.
The extra .1 is there because we also need to account for the fact that some people will pass away before having children, so in order to replace those people, another family will need to pick up the slack and have 3 children instead of just 2. Assuming the 2.1 number you gave is accurate, then that .1 is accounting for the rate at which people pass away without having children. It would mean the *average* of all families having children should be 2.1. Some families could have more while others could have less.
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