Sore little heads ... If it's just a headache, the right treatment will have your child soon back to their normal happy self.

My father had dark eyebrows that would descend lower and lower over his sad brown eyes when fate struck him a particularly vicious blow. So as he sat spooning up his soup on those black nights when my mother announced that each of the five children needed a new school uniform, his head would drop almost into his plate until all we could see was the top of his dark head and those thick eyebrows.

The night she told him we had dug a swimming pool in the backyard into which our neighbour had backed his car, he sat for a long time, his hand motionless, the spoon still in his soup. He finally said with a low groan, ''Oh, well, we'll all be dead soon.'' This cheered him up just enough to finish his soup.

I thought of him as I watched a video of one of John Berryman's Dream Songs:

''There sat down, once, a thing on Henry's heart/so heavy.''

It's bad news for all of you with a similarly gloomy parent, because the evidence is in - we do have a genetic tendency to that thing that sits on the heart so heavy, or to its opposite, the bird that perches so lightly on, or in, the heart. The scientific jury is still out on the exact mechanisms, but consensus is that at least 50 per cent of our tendency to be happy or sad is genetically based. And recent research suggests that we have a set point to which we return after a period of particular happiness or sadness. Say on a scale of one to 10 your set point is three - you're a Henry. If it's eight, you're light-hearted. How lucky you are.

Let's be grave about lightness just for a moment. For Aristotle, fire and air had a natural lightness so that they moved upward, while earth and water had a natural heaviness and moved downward towards the centre of the universe. Not much has changed in the way we think of them. With the weight of the element goes a sense of its energy. Fire and air are bright, quick, ethereal, while earth and water are heavy, slow-moving, tangible. And the upper regions, the ether, where, in most if not all religions, the higher beings dwell, are luminous. We can't even say the word ''light'' without being flooded not only with the visual sensation of it, but with a sensation of lift felt in the whole body.

So it is with light-heartedness. It is quick, bright, lithe. Clods of clayey earth - life, friends, as Berryman says - may be flung at it, but they do not clump and cling. Light-heartedness is the cat walking along the splintery fence-top of life, the hair that curls in the rain no matter how hard life puts on the straighteners. It's the chi in the belly of the leaping dancer. And it's tough, the way that cats and hair and dancers are tough. It's tough the way Perseus is, flying on winged sandals, using his lightness and his balance on the winds, to cut off Medusa's head.

Balance on the winds: what a good way of describing this lively and mobile form of emotional intelligence. Balance is the difference in the way a bird uses the wind and a feather is used by it. Light-heartedness is the lightness of the bird, not of the feather.

My father was one of those oil-soaked pelicans, bowing its beak under the weight of its sodden feathers, unable to break the surly bonds of earth.

Can you learn to be light-hearted? Can you get the oil out of the pelican? Proponents of the learned optimism school say you can teach yourself to be more optimistic. The irrepressible Albert Ellis, guru of the rational-emotive school of psychology, wrote a book called How to stubbornly refuse to make yourself miserable about anything. Yes, anything. OK, and thank you, Albert. You've got me out of a few tight spots. You've shown me how to keep away from the oil.

But it isn't the same thing. Light-heartedness is a gift, like the innate physical co-ordination of the dancer, the tunefulness of a good voice. If you missed out on it at birth, remember it the next time you find a stoppered jar cast up on the seashore. Open it. If a genie comes furling out in a cloud of smoke and offers you just one wish, you know what to ask for.