> When more children live, you get one generation that’s relatively big.
> Then, when families decide to have fewer children, the next generation is much smaller.
> Eventually, a country ends up with relatively more people in the labor force producing economically—and relatively fewer dependents (very old or very young people).
What happened to the now old people in the bigger first generation?
On a more serious note, I assume that they compare the situation with the previous generation.
Generation one dependents: 2 parents, 4 grandparent's, 6 kids, let's say.
Generation two dependents: 2 parents, 4 grandparents, 2 kids.
I'm guessing this is what they mean, maybe I misread it?
There's a large gap that a society must cross to go from third-world to developed. Education, infrastructure, technology, culture, and politics, and career changes take time and money, and when you're competing against other nations making the same transition, and others exploiting the system through corruption, black markets, disguised slavery, wealth extraction by foreign corporations, etc. it's very difficult to make the transition.
I believe that the assumption is that after making the transition, the resulting society will have sufficient economic excess that it will be able to support the large elderly population and will be better off in the end.
Lets say that the average number of surviving children per couple is 2, then 4, then 2 again. The children/parents ratio for the 2nd/1st generation is 4/2=2. The next generation is 2/2=1.
Assuming that the average number of surviving children was about 2 per couple before all this, then the ratio basically returns to normal. The only abnormal ratio is the large generation compared to the previous one.
After the large generation, the population is just bigger. But the gen1/gen2 ratio is normal. The population doesn't shrink back down to pre-boom levels.
Previous: 2 Old / 4 Adult / 20 children born, of which 10 survive = 3 dependents per adult
"1. bigger gen" = 2 Old / 4 Adult / 20 children, all surviving = 5.5 dependent / adult
"Next generation" = 4 Old / 20 Adult / 60 children = 3.2 dependent / adult
"eventually" = 20 Old / 20 Adult / 20 Children = 2 dependent / adult
(Real numbers are better than this b/c productive adulthood is more than 1/3 of life. It's simplified here to make the math easier to follow).