Study: Climate Change trumps Natural Selection

A new wrinkle on the theory of evolution has been added as a result of 24 years worth of study of shrinking Scottish sheep from the Hirta Island. The average body size of the sheep has decreased by 5 percent during that time and the reason being posited by scientists is that the warmer climate is responsible.

Where only the largest and strongest sheep could survive the harsh winters before, the milder weather means that lambs don't require as much weight in their first year of life; slower growing sheep now have the opportunity to survive as well. Classic evolutionary theory indicates that the sheep should grow larger with the offspring resembling the parents while the opposite is occurring.

"Our findings have solved a paradox that has tormented biologists for years - why predictions did not match observation," stated Tim Coulson, researcher and lead author of the study from Imperial College London. "Biologists have realized that ecological and evolutionary processes are intricately intertwined, and they now have a way of dissecting out the contribution of each."

Another factor involved in the decreasing size of the sheep is the so-called "young mum effect". The researchers have observed that younger females produce smaller offspring than the parent was at birth. While they're uncertain of why this happens, they point out that the effect counters natural selection. "But it is not enough to explain why they're shrinking. We believe that this is down to climate change. These two factors are combining to override what we would expect through natural selection."

The increased availability of food for longer periods of the year combined with less severe winters mean that weaker sheep are surviving in larger numbers. The team used body weight measurements and key life milestones for analysis with a group of female sheep.

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