Brebner asks whether if GDP started growing at phenomenally higher rates than expected, wouldn't that challenge Ferguson's framework about warfare being the primary signal of historical development?

The possibility that economic constraints might be removed for large populations, shifting whether people have more children, depends on understanding the actual preference function for children independent of economics.

Jonathan raises the question of whether there is a 'natural' preference for children when economic constraints are removed, suggesting that the relationship between fertility and economic incentives may be more complex than Ferguson's deterministic account.