How to defuse the population time bomb and save humanity from ourselves

The Earth’s too crowded, so better family planning may be humanity’s last hope to save us from ourselves, write Zo Schlanger and Elijah Wolfson

When night falls on Kibera, it is like a door slamming shut.

When the sun is up, things are hectic and loud, rough and fetid, but always safe and even welcoming: Bright colours abound and so do offers of nyama choma (roasted meat, usually goat) and bottles of Tusker, the local lager.