At the risk of sounding cynical, one of the reasons why population growth attracts more attention is because it shifts the discourse away from more substantive issues of 'access to and ownership of assets by the poor' and distribution of resources.
As Mark as had pointed out, investing in women - through education and health care - can lead to substantive reductions in family size but despite evidence to this effect the preference for male children and the patriarchal mind-set that is pervasive, inhibits adequate investment in women. We need to invest in young people and particularly young women - given the demographic transition in many countries - and we need to ensure property rights and access to commons for the poor.