Looking at the experience of industrial countries, the best way to cut population growth is through economic growth, increasing lifespan and by ensuring that people have something other than their children to see them through old age.

And before you go sterilizing 12 year olds, from a biological point of view, increased competition for the right to breed and killing off those who cannot breed would both be better for the species.

Thank God our values are not purely Darwinistic.