BERLIN -- Some human traits that are linked to sunlight -- including mood and sleep patterns -- may be influenced by a person's Neanderthal forefathers, according to a study published Thursday.

Researchers examined the genome of more than 100,000 Britons who inherited DNA from Neanderthal ancestors and found they reported higher rates of listlessness, loneliness, staying up late and smoking.

The study by scientists at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, also confirmed that some Neanderthal DNA found in people of non-African descent affects their skin and hair colour, though not in any single direction.

The findings suggest Neanderthals were already well-adapted to low and variable levels of sunlight in Europe when modern humans first arrived there from Africa some 50,000 years ago, said Michael Dannemann, who co-authored the study published in the American Journal of Human Genetics.

Scientists have known for years that Neanderthals and modern humans interbred. About 2 per cent of the DNA of people of non-African descent comes from Neanderthals, a species that became extinct about 40,000 years ago.

Previous studies have examined the link between diseases and Neanderthal DNA, concluding that the ancient DNA can influence illnesses such as diabetes.

Dannemann and his colleague Janet Kelso decided to look at the impact of Neanderthal DNA on non-disease traits in modern humans. They compared DNA patterns from 112,338 people of British ancestry stored in a databased called the U.K. Biobank with the genome of a Neanderthal found in southern Siberia, near the Russia-Mongolia border.

They were able to link 15 physical traits to Neanderthal DNA, including several traits for hair and skin colour but also behaviour, such as a person's 'chronotype' -- that is, whether they are a morning or an evening person. Those with specific sections of Neanderthal DNA were noticeably more likely to describe themselves as an evening person.

"What we could see is that most of them correlate to how much exposure to sunlight you have," said Dannemann.

In a separate study, published Thursday in the journal Science, researchers examined the DNA of a Neanderthal genome found in a cave in Croatia.

The paper, also co-authored by scientists from the Max Planck Institute for Evolutionary Anthropology in Leipzig, describes Neanderthal DNA found in modern humans that has been linked to eating disorders, rheumatoid arthritis and schizophrenia.

"This adds to mounting evidence that Neanderthal ancestry influences disease risk in present-day humans, particularly with respect to neurological, psychiatric, immunological, and dermatological phenotypes," the authors conclude.