A British tree thought to be up to 5,000 years old has started to change sex, a "rare and unusual" phenomenon not fully understood by scientists, a botanist said Monday. The Fortingall Yew, in Perthshire, central Scotland has for hundreds of years been recorded as male, but has recently begun sprouting berries, suggesting that at least part of the tree is changing gender. "It's a rare occurence ... rare and unusual and not fully understood," said Max Coleman of Royal Botanic Garden Edinburgh, who spotted the berries. "It's thought that there's a shift in the balance of hormone-like compounds that...