Things look black for isle sheep

Published on Thursday 17 January 2008 21:01

A FLOCK of sheep living on a remote Scottish island do not contradict Darwin's theory of evolution, a scientific study has found.

There were concerns that the number of dark brown Soay sheep on the island of Hirta in the St Kilda archipelago had decreased over the past 20 years, relative to those with sandy-coloured coats, even though the latter animals were smaller.

Large size is usually linked to survival and reproductive success, and this seemed to present a problem for Darwin's theory. However, researchers from Edinburgh and Sheffield universities and the Queensland Institute of Medical Research in Australia discovered the gene for the darker coat is usually co-inherited with a set of genes which increase size but decrease reproductive success.

The light-coat trait among the sheep, which live wild on the island, is usually co-inherited with genes which decrease size but increase reproductive success.

Dr Jacob Gratten, of Sheffield University, said: "The study addresses an important problem in evolutionary biology. It shows that predicting the evolutionary response to selection is difficult without knowledge of which genes are in close proximity to each other.

"It also highlights that an understanding of the underlying genetic basis of a highly visible trait was necessary in order to understand its evolution," he added.