Agreed. 'Biggest tribe wins' is a dominant instinct and probably the hardest to tame. It has been noted here (and elsewhere I'm sure) that an enlightened society that restricted it's population might nevertheless be overwhelmed by a society with a natalist ideology. It has also been noted that prosperous and secure societies tend to have lower birthrates. But this effect may not in its natural course be strong enough to achieve sustainable population, and in any event our run of prosperity may be challenged in the coming decades.

Strong population controls can have an impact, and quickly, perhaps 1-2 generations. China's current ascendancy has at least a little to do with the better alignment of population and resources that began in the 1970s with the 'one child' policy. It would be ironic if China gives that up in their current expansive phase, as the more prosperous push for larger families.

I believe China is exceptional in its ability to adopt broad policies across such a large population and geographic area. Further, one child per family is extreme, and creates a lot of distortions such as female infanticide and sex-selective abortions.

If restricting reproductive rights is at all possible, I think it has to involve a tradeable ration or permit system. Each female gets, say, 2.2 permits at the time of their birth, and surrenders 1.0 permits when they bear a child. Permits could be traded, with the price providing an implicit value allocating the preference for large vs. small families. Reduced allocations over time would reflect long-term sustainable population goals.

I would favor allocating all the permits to girls, to counter the observed bias toward boys.

Plenty of holes exist in such a scheme. People may try to have more children than they carry permits for, raising the question of enforcement. If one society implements such a scheme and others don't, sustainable population goals may not be reached.

However, reproductive rights and ultimate population are thorny questions. If we are going to address them at all we should be looking at plans that make the highest allowance possible for individual preferences. I think we have a better chance of adapting to a tradeable permit system than to a one woman/one child-type mandate.

A quick google shows Rwanda is the most densely populated country in Africa - 183 per sq km in 1981 and 345 per sq km in 2000.

Jared Diamond talks about this in Collapse but I thought I'd just check the figures. I wonder if they're encouraging smaller families for everyone?