The team found that the component in human DNA, which activates depression, was also present in dinosaurs and would have helped determine their moods.

Using revolutionary technology, the scientists identified the genetic "switches" they believe turn off and on genes that control our behaviour and moods.

According to the team, the switches, also known as "enhancers", have not changed in human genes for hundreds of millions of years.

To make the link between humans and dinosaurs, the researchers examined the DNA structures of other species of animals and birds.

They believe that these enhancers may hold the key to understanding the causes of depression and shed light on why some people develop the illness while others, with a similar genetic make-up, do not.

Though the enhancers are found in every animal alive today, their position has remained unknown until now.

"It appears the switch that drives the gene (which causes depression] seems to have controlled feelings of fear and anxiety in our ancestors 300 million years ago," the Scotsman quoted Dr Alasdair MacKenzie, senior lecturer at Aberdeen University, who is leading the study, as saying.

"The difference is that, originally, it was part of our survival system. The pathology of this gene now is people suffer these same feelings of fear and anxiety when they don't need them," he added.