According to Dr Sinclair's theory, which he calls xenohormesis, animals rely on such botanical stress signals to give them extra information about their own environments, in the same way that the alarm calls of one species warn others of danger.

ECONOMIST: How to live longer��maybe

Critics warn of the danger of so many young people having their formative experiences of alcohol without the supervision of bar staff and bouncers.

BBC: Why fake ID is an American rite of passage

Twitter is emphasising that it acted rapidly to warn people the moment that it spotted the danger - but there is still little information about the nature of the attack or why just one small section of users is in danger.

BBC: Twitter's most serious security crisis

One of the officials said Obama challenged his economic team to "think bolder" as some economists warn there is danger in the government doing too little to curb the recession.

CNN: Obama ups jobs goal to 3 million on bad economic news