St. Kilda, a tiny island off the coast of Scotland, has been home to a wild flock of dark-coated Soay sheep since 1932. Global warming is the suspected culprit that's causing the sheep to grow smaller in size, but according to the Independent, it’s not what's causing the animals' coats to get lighter.
Previous studies suggested that the physical changes in the sheep were due to a warming climate, but a group of scientists now says that is not the case.
According to the Independent, “A study last year by Shane Maloney of the University of Western Australia suggested that dark coats are more likely to absorb solar radiation, giving the darker sheep an advantage over their lighter-colored counterparts in cold conditions. The scientists argued that warmer conditions allowed more lighter-colored sheep to survive, gradually increasing from about 25 percent to 30 percent since the mid-1980s.”
Dr. John Slate of Sheffield University and his team of scientists say that for Maloney’s hypothesis to be true, it would require a difference in survival rates and breeding success in white and dark sheep.
According to genetic research on the St. Kilda flock, the dark coats come from two different genotypes or varieties. Both genotypes have the dark-colored coats, but only one of them has a higher breeding success.
"We're not saying that climate change is irrelevant to Soay sheep. It's just that it doesn't explain the change in coat color that we have observed," Slate said.
Slate went on to tell the Independent that a more probable explanation is that the genes determining coat color lie in a region of the sheep's chromosomes containing another, as-yet-unidentified gene that confers some advantage to the sheep. In this scenario, the change to the flock's coat color is occurring simply because it is "hitch-hiking" with the other mystery gene.
If Slate’s hypothesis fails, there’s always the possibility that the flock was just tired of being the black sheep of Scotland.