THE windswept, rain-lashed island of St Kilda might seem an odd place to unlock the secret of happiness. But now, a study of the island's rare sheep has helped scientists understand why ordinary Scots might be feeling unhappy.
Certainly, the credit crunch, rising prices, economic uncertainty and war would be reason enough to feel a bit blue. But it now seems genes are also to blame for how down in the dumps we feel, particularly when winter arrives.
The research, carried out by Scottish scientists, suggests the chances of feeling depressed during the darker months can vary from person to person.
And the key to who is affected lies in whether their body contains the remnants of an ancient biological mechanism which once controlled the seasonal lives of mammals and invertebrates at least 350 million years ago.
Soay sheep were used by researchers from Aberdeen University because they are thought to be the most primitive species of domestic sheep found anywhere on the planet, and may have first arrived in the Hebrides with the first human settlers about 4,000 years ago.
Unaffected by breeding programmes, the Soay sheep's habits and behaviour are controlled by their bodily hormones and secretions.
The research has now identified a new role for a chemical known as the thyroid-stimulating hormone (TSH) – which is secreted by cells in the pituitary gland – in controlling the sheep's seasonal behaviour.
Dr David Hazlerigg, the leader of the research team and a reader in zoology at Aberdeen University explained: "In order for animals to breed seasonally at a higher latitude away from the equator, they use the annual cycle of day length to synchronise their annual clock.
"We were interested in working out how that programme of synchronisation leads to changes in the brain which, in turn, leads to changes in appetite, their metabolism and what hormones are secreted and switch on or off the breeding cycle.
"We've discovered there is a small group of cells in the pituitary gland which produce this TSH and use it in a way that wasn't perviously appreciated."
Dr Hazlerigg said the team's research challenged accepted wisdom on the relationship between the brain and the pituitary gland.
He said: "What we have is the pituitary controlling the brain instead of the brain controlling the pituitary.
"Instead of going off to the thyroid gland, the thyroid-stimulating hormone goes straight from the pituitary gland – just under the brain – back into the bottom of the brain where it is doing things that we don't yet properly understand, but which lead to changes in the reproductive activity in the sheep and probably to other wider changes in the sheep's metabolism."
The team is convinced these hormonal signals can be traced back through evolution at least 350 million years, to when mammals and birds diverged.
The mechanism could be connected to the occurrence of Seasonal Affective Disorder (Sad), a form of depression that is brought on by the shorter days during autumn and winter and is estimated to affect one in 20 Scots.
Dr Hazlerigg said: "We believe this mechanism is a survivor because it so important to timing the changes in your biology to the annual changes in the seasons.
"In our own ancient past, it is likely we had a very strong seasonal biology. Modern life has removed the need for that because we have central heating and street lights and so on. But evolution takes a long time to change, whereas social evolution can happens very quickly."
He added: "Perhaps there are some humans who have retained remnants of this ancient seasonal timing mechanism – a synchronisation to the natural light-dark cycle which means that they go into a winter-like state."
Forget the Soay, how do we stay happy as times get tougher?
TO IMPROVE your mood, you need to put your situation into context.
You have to think, "OK, we are in a credit crunch, but so is everyone else". It is not our economy which is suffering, it is the world's. In many ways, we are the best placed of the European countries. We have to be more positive.
You have to ask if your standard of living is really that bad.
Maybe things are not as good as they were two years ago – but they are a heck of a lot better than they could be.
People are feeling insecure financially and in their jobs. But if you look at the figures again, even where unemployment is increasing, it is not bad. People are retaining their employees.
The more optimistic you are, the better things will get.
But if you are really, really feeling bad about your job and you see people going, you should keep doing your best but also look around for other options so you have some control.
The more you are in control, the less you are going to be doom and gloom.
If you are all doom and gloom, you get doom and gloom – it is a self-fulfilling prophecy.
There are also other practical things you can do.
If you need some sun, you can still go away for four or five days. Just jump on a plane. We are still relatively well off.
Take a long weekend and go somewhere if the weather is going to be good in the UK.
You do not have to go far, but you will feel better.
You can also ask yourself, "What can I do that's a little bit different?"
Try something you don't normally do and organise it so you can look forward to it. That will really help.
Or why do you not just treat yourself to something enjoyable? People need a treat when they feel low.
There is the old wives' tale about the women who get their hair done when they feel down. Why should that not apply to all of us?
That would help the economy too – it would stimulate it and show that people are robust.
The most important thing in life is to take control.
What is worrying people now is that they feel they do not have control over events – but things could be a lot worse.
• Cary Cooper is a professor of occupational psychology and health at Lancaster University.