The gene responsible for controlling the hours of sleep an individual gets and why some people have their own internal alarm clock has been identified by scientists.
Karla Allebrandt and her team from the Ludwig Maximilians University of Munich identified a gene called ABCC9 that can reduce the length of time we sleep.
The discovery is expected to explain why light sleepers, such as Margaret Thatcher, are able to get by on just four hours shut-eye a night.
The Europe-wide study of 4,000 people from seven different EU countries saw the volunteers fill out a questionnaire assessing their sleep habits.
The researchers then analysed their answers, as well as participants' genes.
They discovered that people who had two copies of one common variant of ABCC9 slept for "significantly shorter" periods than people with two copies of another version.
Having already established that the ABCC9 gene was also present in fruitflies, the team were able to modify it in the animal and shorten the length of time for which it slept.
"Apparently the relationships of sleep duration with other conditions such as heart disease and diabetes can be in part explained by an underlying common molecular mechanism," the Daily Mail quoted Allebrandt as saying.
"The ABCC9 gene is evolutionarily ancient, as a similar gene is present in fruitflies. Fruitflies also exhibit sleep-like behaviour.
"When we blocked the function of the ABCC9 homolog in the fly nervous system, the duration of nocturnal sleep was shortened," she added.