Paul Allen (listed by Forbes as the world’s 37th richest man) has pledged to hand over at least half of his estimated $13.5bn (£8.8bn) fortune to charitable causes. The move comes just one month after his one-time business partner Bill Gates and billionaire investor Warren Buffet initiated a campaign to encourage billionaires to give more money to charity ( the ‘giving pledge’). Allen has highlighted not-for-profit scientific research as a field in which he would like to see a significant proportion of his wealth invested in.