This Crooked Timber post on declining population has prompted me to get started on what I plan, in the end, to be a lengthy critique of the pro-natalist position that dominates public debate at the moment. My initial motivation to do this reflected long-standing concerns about human impacts on the environment but I don’t have any particular expertise on that topic, or anything new to say. Instead, I want to address the economic and social issues, making the case that a move to a below-replacement fertility rate is both inevitable and desirable.
I’m going to start with a claim that came up in discussion here and is raised pretty often. The claim is that the more children are born, the greater the chance that some of them will be Mozarts, Einsteins, or Mandelas who will contribute greatly to human advancement. My response was pre-figured hundreds of years ago by Thomas Gray’s Elegy Written in a Country Churchyard. Gray reflects that those buried in the churchyard may include some “mute inglorious Milton” whose poetic genius was never given the chance to flower because of poverty and unremitting labour
But Knowledge to their eyes her ample page
Rich with the spoils of time did ne’er unroll;
Chill Penury repress’d their noble rage,
And froze the genial current of the soul.
Billions of people alive today (the majority of whom are women) are in the same situation today, with their potential unrealised through lack of access to education and resources to express themselves. Rather than adding to their numbers, or diverting yet more resources away from them, we ought to be focusing on making a world where everyone has a chance to be a great poet or inventor.
Foreshadowing future argument
The political difficulties of achieving the necessary redistribution are immense. We are unlike to achieve even the basic targets set out in the Sustainable Development Goals for 2030. But even supposing that the world were a fairer place, it is unlikely that we can provide the kind of education necessary for full participation in a modern economy while having more than two children each (that is, more than one child per parent) on average. The fact that fertility rates in all development countries are below this level is a reflection of economic reality, not the product of social decadence. I’ll be expanding on this point a lot, so I’d welcome it if the discussion focused on the main part of the post.
John Quiggin 
There is a famous legend about the boyhood of Carl Friedrich Gauss that illustrates Gray’s and JQ’s point with a happy ending, with the additional advantage of being basically true. One modern retelling:
“In the 1780s a provincial German schoolmaster gave his class the tedious assignment of summing the first 100 integers. The teacher’s aim was to keep the kids quiet for half an hour, but one young pupil almost immediately produced an answer: 1 + 2 + 3 + … + 98 + 99 + 100 = 5,050. The smart aleck was Carl Friedrich Gauss, who would go on to join the short list of candidates for greatest mathematician ever. Gauss was not a calculating prodigy who added up all those numbers in his head. He had a deeper insight: If you “fold” the series of numbers in the middle and add them in pairs—1 + 100, 2 + 99, 3 + 98, and so on—all the pairs sum to 101. There are 50 such pairs, and so the grand total is simply 50×101. The more general formula, for a list of consecutive numbers from 1 through n, is n(n + 1)/2.”
I say this legend is true because Gauss came from a working-class family. Wikipedia: “His father … worked in several jobs, as butcher, bricklayer, gardener, and as treasurer of a death-benefit fund.[…] his wife Dorothea, Carl Friedrich’s mother, was nearly illiterate.” Boys went to school in the duchy of Hannover, but it was a pretty basic school. Gifted kids like Carl Friedrich are a problem for teachers, and it was against the odds that this particular schoolmaster recognized that this boy was not just bright - there is at least one in every class – but a one-in-a-million talent, and gave him the first essential push up he first rung of a very high ladder. He could just as easily have crushed the talent with ridicule and neglect, as surely often happens. Interesting that as a famous scholar, Gauss worked like his father on the problems of a pension fund, inventing statistics on the way.
PS. You can have a go at putting a number to the Gray undercount. Assume that potential genius is 100% genetic and randomly distributed. Draw up a list of fulfilled geniuses and allocate their family background to an income class, say rich (Darwin, Maxwell, Tolstoy), middle (Newton, Shakespeare, Bach) and working (Gauss, Faraday, Mendeleev). Estimate the shares of these classes in the general population. Compare with the class ratios of the geniuses. The difference is the Gray undercount. One problem is that class ratios change overtime, and the geniuses are too few to break up by period. Herr Professor Dr. Gauss may have a fix.