For the fourteenth year running, Japan's population has slumped to a record low. The non-foreign population dropped by nearly 900,000 — an unprecedented fall.
Let’s assume for a second that in society X every couple has one child at the age of 30 on average, and that child mortality doesn’t exist. In that case the average couple has to care for one child and four grandparents for a total of 2.5 dependents per working adult. That’s an inverse pyramid; there are more old people than young people. The older humans are the more likely they are to die, but also when they die new old people come to take their place so it cancels out. Anyway for comparison let’s consider society Y where every couple has two children on average. In that case two sets of grandparents will give birth to four children who will then have four children in total, producing a cuboid and a ratio of 2 dependents per working adult. More than 2 and you get a pyramid at the bottom.
People are always born with the same age namely 0, but they do not all die at the same age. In fact getting older increases chances of death. Hence 2 babies per mother ends up in a pyramid too.
Even if you presume people all die at the same age, things will be stable. If say people all get childten at 30 and only work between 30-60 and then all die at 90. If we then assume 1 child per couple and everybody has a child at 30, we would get a stable dependency ratio of 2.5 dependents per worker. Obviously those numbers are not realistic. Btw that also is not a pyramid, but a trapezoid.
Let’s assume for a second that in society X every couple has one child at the age of 30 on average, and that child mortality doesn’t exist. In that case the average couple has to care for one child and four grandparents for a total of 2.5 dependents per working adult. That’s an inverse pyramid; there are more old people than young people. The older humans are the more likely they are to die, but also when they die new old people come to take their place so it cancels out. Anyway for comparison let’s consider society Y where every couple has two children on average. In that case two sets of grandparents will give birth to four children who will then have four children in total, producing a cuboid and a ratio of 2 dependents per working adult. More than 2 and you get a pyramid at the bottom.
People are always born with the same age namely 0, but they do not all die at the same age. In fact getting older increases chances of death. Hence 2 babies per mother ends up in a pyramid too.
Even if you presume people all die at the same age, things will be stable. If say people all get childten at 30 and only work between 30-60 and then all die at 90. If we then assume 1 child per couple and everybody has a child at 30, we would get a stable dependency ratio of 2.5 dependents per worker. Obviously those numbers are not realistic. Btw that also is not a pyramid, but a trapezoid.