Every day is a happy one

'At no point in history has a smile been so pronounced or carried so much importance. While this makes me feel uncomfortable, it will probably suit Astrid just fine.'

Employees at the Keihin Express Railway in Japan are scanned by cameras and judged by computers to ensure they smile enough at work. The Omron Smile Scan system analyses the faces of more than 500 staff at 15 train stations on the company's network in Tokyo and awards them a score between zero and 100. Smiling, the company says, creates a more relaxed atmosphere and helps staff to deal with customers more effectively.

I was in the car when I heard this news on the radio. I was not smiling at the time because there's not much to smile about while driving around Abu Dhabi. I might have mustered a rictus a few minutes earlier when a bus veered into my lane at a roundabout, but in general I remained glum throughout the journey. When I glanced in the rear-view mirror, Astrid, on the other hand, was beaming. She would have excelled at the Omron Smile Scan. I'm often told she is "a very smiley baby". She smiles when she wakes up. She smiles when she is playing. She smiles when she is eating. Sometimes she even smiles when she is sleeping. It is possible to stem her tears with a persistent bout of smiling or defuse a bad event, such as knocking her head on the table or skidding on the tiled floor, with a parental grin. Equally, Astrid can lift my flagging spirits and fatigued limbs with a smile.

Smiling is a complicated and primal gesture. In a famous and oft-quoted experiment, two rhesus monkeys trapped together in a cage were at first very wary of each other, then they became a bit aggressive and finally they showed their teeth - forming something akin to a smile - to express fear and convey good intentions. The display of teeth, a close relation of the human smile, defused a tense situation.

In fact, we start to smile before we are born. Babies smile, cry and blink in the womb. In 2003 Professor Stuart Campbell pioneered new scanning techniques which picked up a range of facial expressions by unborn babies. Smiling, he said, could turn out to be a reflex, rather than learnt behaviour. Turning the corners of our mouths upwards is a gesture which gives "some indication of contentment in a stress-free environment".

We are, I feel, heading into a smilier future. Portraits in the 17th century by painters such as Rembrandt and Velásquez did not depict much smiling. Almost without exception, subjects were serious and flinty. Even one of art's most famous smiles - the 16th-century portrait of Mona Lisa by Leonardo da Vinci - is profoundly ambiguous. It turns out to be a trick of the brain, which has recently been explained by Spanish neuroscientists. Apparently the reason the subject in the painting appears to waver between smiling one moment and being serious the next has something to do with the different visual channels in our brains and which one is dominant at a particular moment.

Perhaps photography is partly responsible for rise of the grin in the 20th century. "Smile for the camera" or "say cheese" prelude most snapshots. Celebrities smirk and simper for the lens. The sombre aesthetics of Rembrandt are reworked in his dazzling 21st-century namesake: Rembrandt Lightening Gel promises to "restore your smile to its natural luster". At no point in history has a smile been so pronounced or carried so much importance. While this brave new world makes me feel a bit uncomfortable, it will probably suit Astrid just fine.

Astrid is unfazed by fireworks. It was as if seeing the sky explode in cascades of light and colour was something that happened every day. At the next table a child sat on a woman's knee. The woman had her hands over the child's ears to protect her from the noise and stop her from being frightened. Meanwhile, Astrid was getting bored. After five minutes she started playing with the tablecloth and only glanced up now and again when a particularly booming sequence exploded.

It is often surprising what Astrid finds surprising. Earlier she noticed the light fade and the onset of darkness. Clearly being out at a time when she is often in bed was unusual. She kept craning her neck and arching her back to look upwards at the night sky. She was fascinated. At the moment Astrid has a glut of potential wonder: fireworks displays cannot compete with the daily sinking of the sun.