In many countries, a gap obtains between the actual fertility rate and what is perceived as the optimal fertility rate. In some cases, fertility is deemed too high, typically out of concern for the ability of our natural environment to cope with such an anthropic pressure (climate change being a possible example) or for the capacity of the land to feed and provide enough space to so many people (a motive present, among others, in China's one-child policy, see Greenhalgh (2003)). In other cases, the actual fertility is perceived as too low. It can be due to the need to be numerous enough to support an endangered cultural identity, for example. In some cases, it is the relative size of the various cohorts coexisting in a country that is at stake, a low fertility rate being one of the factors threatening the financial viability of pension schemes and health care systems. Other concerns about relative size of different groups within a population arise as well with respect to ethnic composition or educational level, fertility and mortality rates differing along such characteristics.

In the presence of under-population, various measures have been proposed and adopted. For example, at least in some contexts such as post-World War Two, one justification for the introduction of family benefits was a pro-natalist one. Other measures include extensive parental (paid or unpaid) leave schemes, parent-friendly workplaces or the public provision of day-care. More recently, it has been argued that linking pension benefits to fertility would be a way to restore optimality (see Schoonbroodt and Tertilt (2011)).