Shearing The Shrinking Sheep Myth

An article from the French press recently made headlines by outlining the “case of the shrinking sheep“.  It seems that the wild Soay sheep in a little place called Hirta, in the St. Kilda archipelago in the Outer Hebrides of Scotland, are defying Darwin and the evolutionists by becoming smaller in size as their population ages.

Hirta is a little storm-battered island only just over 2 miles square and when its last small settlement of human inhabitants finally left in 1930, taking their sheep with them, the only fauna remaining behind were the seabirds, seals, and the St. Kilda wood mouse.   The Soay sheep were introduced in 1932 to roam freely and the area eventually became a wildlife refuge.

The average person just doesn’t spend much time thinking about biological diversity and the reasons for it, and brave little sheep on a wind-swept isle in romantic Scotland make for wonderfully guilt-inducing photo ops.   But there is something wrong with this picture.

Every ecosystem has an inherent set of checks and balances and in the case of Hirta, what is missing from the traditional and expected picture is a natural predator of the sheep.  The wild Soay sheep on Hirta have lived with no pressure from anything except their physical surroundings and, naturally, this increases the chances of survival for the small and the weak.  But despite their unpressured existence, studies have shown the population fluctuates with “periodic population crashes, during which up to 60% of the population may die. The adult sex ratio is strongly female biased due to heavily male biased mortality during population crashes.” 

There is also the matter of inbreeding, and although one study shows Soay sheep to be less likely than other species to mate with close relatives, the inherent small numbers of the population and limited habitat naturally depresses the availability of genetic diversity over time.

The fear-mongers who beat the voodoo drums of global warming to conjure up their own future financial windfalls want you to believe that the wild Soay sheep are shrinking like a wool sweater because of being tumbled in a hot man-made dryer, but don’t let them pull the wool over your eyes.  Common sense looks for an explanation that actually meets the criteria of reality; because of my own work I know that there are numerous exceptions in this wonderful world to what is called “Bergman’s Rule”, a biological observation that says members of a species tend to be larger in the cooler part of their range.  When you look at the circumstances in which the wild Soay sheep live on Hirta their slightly smaller size today – a phenomena still unfolding – is far more likely due to a naturally-belated exception-to-Bergman’s-Rule response to the previous, slight warming trend the Earth has recently experienced, then combined with a previously-unneeded but hearty “small size” gene becoming dominent due to the naturally slow rate of inbreeding combined with the lack of natural predation.

And such exceptions do not conclusions make.  Unless, of course, you’re out to fleece someone.