[markwkw]

These two effects are not similar in scale. Fertility across the globe is falling by a lot. Africa went from 6.7 to 4.2 in a span of 50 years. Asia went from 6 to 1.9.

Anywhere but least developed countries child mortality is low, such that fertility replacement level is estimated at 2.1 (vs 2.0 if everyone survived until reproductive age).

We used to have 5-6 kids, with one dying if you were a bit unlucky (statistically speaking). Now we have 2 or less.

[smeej]

Sure, it's not the full cause of the fall in birth rates.

Somehow it had just never occurred to me that of course any family that has an "ideal size" is going to have fewer births if all the children survive than it will if one or more of them die, and now I'm trying to figure out what terms I would even look up to find out how much of the effect could be attributed to that.

In other words, how much of the decline in birth rate is due to parents reaching their ideal family size without the death of any children? I'm reasonably sure it's small, but are we talking <1% small or 10% small?

Edit: typo