‘The problem with the gene pool is that there is no lifeguard.’

So, if we're programmed to be negative, cautious and pessimistic, why on Earth was happiness invented?

I love Barbara Fredrickson's model of ‘broaden and build’ because, at last, there's an academic argument that explains the evolutionary significance of happiness. It seems that positive emotion works in exactly the same way that negativity doesn't.

Negative emotions close down your thinking. Danger, for example, narrows down your choices to just two: ‘fight’ or ‘flight’.

Fredrickson argues that the experience of positive emotions opens the mind and enhances our choices. Positivity enhances creativity. Positive emotions fuel enthusiasm, innovation, optimism and drive. They enhance our ability to take in information, increase our capacity for intellectual complexity and our ability to explore alternatives.

Positive emotions generate what Kim Cameron calls ‘upward spirals’ towards optimal functioning. Phew! As well as enabling us to feel good in the now, it seems there might be a valid evolutionary role for happiness and positivity after all.

So, if your ancestors were sitting around in the cold, tearing at pieces of raw meat but managing to feel good about their day's hunting, their minds would open up to possibilities about the future. ‘Hey,’ says your great-great (to the power of 500) grandpa, ‘I've got an idea. What do you reckon would happen if I rubbed these two sticks together?’

And, whoosh, McDonalds is born!

And, once again, this kind of fits with your own experience. When you're feeling down, the world closes in and you can't think of a way out. That's essentially the feeling of depression; locked into negativity, trapped in a world of self-pity, with seemingly no way out.

When you're upbeat, your brain fires off with all sorts of creative solutions. Just about anything's possible.

The big question we want to grapple with is, how? How do we get into a state where our brain is firing and energy zinging? Nobody's ever got to the bottom of this before because they haven't studied deeply enough. Brace yourself, because in the next chapter we're immersing you in the grey goo of quantum mechanics.