Also in several counties and cities, and some parts of Busan and Seoul the fertility rates have reached 0.30 children per woman (And still falling quickly nationwide). How bad and severe this is for SK?
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Let’s say if you have 500 men and women, who are all 30 years old. And let’s ignore things like infertility, premature deaths, and assume everybody lives till 60 and then dies.
With a fertility rate of 2.0, each woman gives birth to 2 babies. Again, let’s assume it’s perfectly 50% sex ratio. So this group of 1000 will have produced 1000 babies, 500 girls and 500 boys. Now you have a population of 2000.
Thirty years later, your first generation dies off. And the 1000 babies have grown into adults, who then produce another 1000 babies. So, with a fertility rate of 2.0, your population stays constant at 2000.
But what about 0.68?
It means your first generation 1000 people produced only 500×0.68 = 340 babies, with 170 boys and 170 girls. You have a population of 1340.
Thirty years later, your first generation of 1000 people dies. The second generation of 340 produces 170×0.68=116 babies, with 58 girls. Your population just dropped from 1340 to 456. That’s a 66% decline in one generation.
Another 30 years passes, the 3rd gen of 58 women produces 58×0.68=40 babies. Second gen of 340 dies off, so you’re left with a population of 156. Similarly, one generation later, with only 20×0.68=14 new babies, your population is now only 54. After another 30 years, you’re at 19.
So a 66% drop in one generation, 88% drop in two, 96% drop in three, and 99% drop in four. Your population practically goes extinct within 3 to 4 generations.
It’s actually worse than this, cuz not all babies make it to adulthood. So the actual replacement rate (fertility rate needed to maintain population) is going to be higher than 2.0.
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