In 2011, when the global population hit 7 billion, economist David Lam and demographer Stan Becker made a bet. Lam predicted food would get cheaper over the next decade, despite continuing population growth. Becker predicted that food prices would go up, because of the damage humans were doing to the planet, which meant that population growth would outstrip food supply. Becker won and, following his wishes, Lam has just written out a cheque for...