Climate change is causing a breed of wild sheep in Scotland to shrink, according to research. Scientists say milder winters help smaller sheep to survive, resulting in this "paradoxical decrease in size". Classic evolutionary theory would predict that wild sheep gradually get bigger, as the stronger, larger animals survive into adulthood and reproduce. Since 1985, the sheep have decreased in size by 5% - their legs getting steadily shorter and their body weight decreasing.
This strange phenomenon was first reported in 2007, but the reason for it remained under debate. "In the past, only the big, healthy sheep and large lambs that had piled on weight in their first summer could survive the harsh winters on Hirta." Because of climate change, grass for food is now available for more months of the year on the island. "Survival conditions are not so challenging - even the slower growing sheep have a chance of making it, and this means smaller individuals are becoming increasingly prevalent in the population." As for the future of the sheep, the team believes that they are still shrinking. "But it's too early to say if, in 100 years, we will have chihuahuas herding pocket-sized sheep."