Gladstone Institute of Cardiovascular Disease, San Francisco, California

A geneticist wonders why we need to sleep.

Scientists can have a love–hate relationship with sleep. We know that it is vital for our health, but not the reasons why. We celebrate dreams that provide inspiration, but often dismiss sleep as a chore.

Yet deep sleep can provide insight into vexing problems. In 1920, pharmacologist Otto Loewi famously had a recurring dream that suggested how he could demonstrate neurotransmission in the lab. The key experimental details escaped him until he captured the dream in a bedside notebook. Later that day, he performed his Nobel-prizewinning experiments with the aid of a few frog hearts and a water bath.

Now, a team led by Ying-Hui Fu reports that a single mutation in a gene called DEC2 can cause people to sleep for only about six hours per night instead of the usual eight (Y. He et al. Science 325, 866–870; 2009). This mutation seems to be exceedingly rare, with only two carriers found so far. Only by introducing this mutation into transgenic mice and fruitflies could the researchers show compelling evidence of the mutation's effect. These two additional waking hours each day are quite remarkable when you consider that, over 80 years, this would add up to more than 8 years of extra productivity!

Why are extreme short sleepers so rare? Surely evolutionary pressures should favour less sleep? In prehistoric times, short sleepers would have had more time to hunt, gather food and guard against predators. In modern society, we must constantly balance home, work and other demands. Sleep is often sacrificed, so a drug that could provide hours of extra productivity would be hugely popular.

A better understanding of the reasons for sleep could provide a rationale for getting more of it. In the meantime, I will keep a notebook by my bedside as a dream catcher.