Our bodies reverberate to an exquisitely regulated rhythm, an ebb and flow dictated by a biological master clock in our brains. It influences when we sleep and wake, the rise and fall of body temperature and digestive enzymes, and when we reach our performance zenith and nadir.
Despite the fundamental control over the biological rhythms of our bodies, how this system operates has remained something of a mystery until recent times, according to Prof Russell Foster, who delivered a Science Today lecture on the subject last night in Dublin.
"It is a fundamental part of all life," Prof Foster told his audience yesterday evening in the RDS Library, Ballsbridge. The event was organised jointly by The Irish Times and the Royal Dublin Society, one of an ongoing series of free public lectures on science and scientific research.
The biological clocks that set the pace of life "evolved shortly after life evolved on Earth", Prof Foster said. "The molecular clock in all life that has been studied so far relies on a core set of genes," he said. The 14 or so genes linked to our biological clocks are the same in the human or a dog, a chimp or a fruit fly.
Research has tracked down the master clock in humans to a tiny cluster of cells in the brain known as the suprachiasmatic nuclei (CSN), he said. "The SCN is the master clock, but it must be adjusted to the local time and the light/dark cycle does that".
Not unexpectedly, our bioclocks match the rise and fall of the sun, a natural rhythm that would have exerted a "massive selection pressure" on the evolution of life on earth, he said. Yet the two remain just slightly out of step.
"It is driven by the light/dark cycle. On average, the human clock under constant conditions gives a day of 24 hours 11 minutes, a little bit longer than an astronomical day," Prof Foster explained.
Prof Foster explained how our biological clocks could influence our daily lives by varying cellular activity through the day. "When driving between four to six in the morning, your ability to make decisions is as hard as if you have had a couple of whiskeys," he stated. Sporting performance tends to peak in the early evening, while decision making is strongest at midday.
He and colleagues discovered how time discrepancies between clock and sun are ironed out. Special cells in the eye not connected with vision help keep the master clock synchronised with night and day.
