Just look at humans. In the tallest nation, the Netherlands, men reach on average 184cm (6ft) and women 170cm (5ft 7in), while in the shortest nation, Timor Leste, men stand at 160cm (5 ft 3in) and women 153cm (5ft). Diet and environment play a large part in why the Dutch have added 20cm (7.9in) to their average height in the past two centuries, but a big part is also played by sexual selection. Being tall in the Netherlands is more attractive, and so the Dutch keep getting taller. (Learn more about why the Dutch are the tallest people in the world on BBC Reel.)