The Nigerian city of Igbo-Ora is home to so many twins, it organises an annual festival in celebration of doubles. Up-to-date stats are tricky to pin down, but a 2002 report from the BBC cited Igbo-Ora’s ‘twinning rate’ as high as 158 per 1,000 births (other countries are closer to 12 per 1,000). Locals believe the phenomenon has to
