Can science explain why I'm a pessimist?
Many of us categorise ourselves as either optimist or pessimist, but what can science tell us about how we got that way and can we change, asks Michael Mosley.
Debbie and Trudi are identical twins.
They have much in common, except that Trudi is cheerful and optimistic while Debbie is prone to bouts of profound depression.
By studying a group of identical twins like Debbie and Trudi, Prof Tim Spector, based at St Thomas' hospital in London, has been trying to answer fundamental questions about how our personality is formed. Why are some people more positive about life than others?
Twin studies suggest that, when it comes to personality, about half the differences between us are because of genetic factors. But Spector points out that throughout our lives, in response to environmental factors, our genes are constantly being dialled up and down as with a dimmer switch, a process known as epigenetics.
With twins like Trudi and Debbie they have found changes in just five genes in the brain's hippocampus which they believe have triggered depression in Debbie.
"We used to say," Spector told me, "that we can't change our genes. We now know there are these mini mechanisms that can switch them on and off. We're regaining control, if you like, of our genes."
From: http://www.bbc.co.uk/news/magazine-23229014