The human body is a machine whose many parts – from the microscopic details of our cells to our limbs, eyes, liver and brain – have been assembled in fits and starts over the 4 billion years of our ...

If you don't have testicles, chances are you are fascinated by them. C'mon guys, I know I'm not the only one who finds them utterly baffling. Despite having seen a fair few (sorry Mum!), I don't know ...