The definition of biological advantage is having a large number of offspring rather than a small one! (Simplifying a bit; said offspring should also reproduce,

The definition of biological advantage is having a large number of offspring rather than a small one! (Simplifying a bit; said offspring should also reproduce, recursively, but it's a decent approximation to just consider offspring.) What kind of weird question is that? It also depends on whether there are malthusian limits applicable specifically to the population that is growing. It's unclear if this is the case in the modern world, but it certainly was the case in the past (availability of food in one place didn't prevent famine in another). In this case, a higher birthrate could technically continue for centuries (or even millennia) before a reckoning, so you might have to go well beyond a single iteration of offspring to know. There's plenty of debate about whether science can save humanity from malthusian limits, so the scenario I described might never come to pass. There are also other ways (wars, territorial conquest, mass immigration) for a high growth population to find a release valve. All in all, though, I'm hopeful that the economist has this right - a non-coercive reduction in birth rates brought on as a natural response to increasing levels of global wealth, peace, and prosperity. Man, that would be an awfully nice way to avoid malthusian catastrophe. And while there's plenty to debate and disagree about, it's encouraging that the data does at least to some extent support this hope.