Survival of the less fit

摘要

On the remote island of Hirta, in the St Kilda archipelago beyond the Outer Hebrides, live hundreds of wild Soay sheep. Over the past 20 years biologists studying this primitive breed, which has not changed much since the Bronze Age, have noticed that the sheep are getting smaller. This was a puzzle because, in general, bigger animals are usually much better at surviving the island's extremely cold winters. The biologists now think that climate change could be involved.rnTim Coulson of Imperial College, London, and his colleagues examined the weights of about 2,000 female sheep that lived on the island in the two decades of their study. They combined this information with detailed histories of individual animals. They found that daughters were, on average, lighter than their mothers had been at the same age. Their legs were shorter, too, suggesting that the breed really was shrinking.