Two polished stone balls shaped about 5,500 years ago – linked to a mysterious practice almost unique to Neolithic Britain – have been discovered in an ancient tomb on the island of Sanday, in the Orkney Islands north of mainland Scotland. Hundreds of similar stone balls, each about the size of a baseball, have been found at Neolithic sites mainly in Scotland and the Orkney Islands, but also in England, Ireland, and Norway, Live Science previously reported. Some are ornately carved – such as the famous Towie ball discovered in northeast Scotland in 1860 – but others are studded with...