Researchers are studying the habits of primitive sheep to better understand how the seasons affect human beings.
Soay lambs look like young deer
The University of Edinburgh has begun studies into Soay, which are found on Scotland's St Kilda island archipelago and are unaffected by cross-breeding.
Scientists have already found that they have a 10-month cycle that regulates appetite, when they fatten and moult.
The study could reveal the secrets of the human "body clock" and how it is affected by winter and night shifts.
Scientists have been investigating the biology of a herd of 50 Soay sheep in Fife.
The breed comes from Soay in the St Kilda group of islands, about 41 miles (65km) from the Western Isles.
The National Trust of Scotland, which owns St Kilda, said the origins of the sheep were uncertain and believed they were brought there by Vikings in the 9th and 10th Centuries.
Dr Gerald Lincoln, of the university's Centre for Reproductive Biology, said the animals' body clocks appeared to be a wild-type unaffected by cross breeding throughout the centuries.
He said: "While our daily - or circadian - body clocks anticipate the change between day and night, our circannual clocks anticipate the seasons as we orbit the sun.
"As our clocks are pre-set and individual, this explains why some people are larks and others owls, and why some suffer severely in winter."
Dr Lincoln said researchers had identified the cells that co-ordinate the human body clock and were now trying to find the specific genes that regulate the body's long-term timing.
He said: "By doing this, we hope to find new clinical treatments.
"It could be beneficial to those working night shift, who suffer poor health and have reduced life expectancy, as well as looking at how our metabolism is regulated throughout the year.
"The calendar genes could even provide new insight into the most basic timed mechanisms of DNA repair and aging."