Generally, we think that animals — including humans — that are protected and well fed will get bigger, not smaller. So the news last summer that some sheep are shrinking came as a surprise. The sheep live in relative isolation on an island off the western coast of Scotland — a remote place, but not so remote as to be unaffected by climate change. Life in the wild is, naturally, brutal: in a typical herd of sheep, a percentage will die during winter because they are too small to survive. Since it's the hardier, bigger animals that make it to spring — and reproduce — over generations, sheep get bigger overall. But thanks to global warming, which yields warmer winters and more abundant grass in Scotland, scrawny sheep are now living long enough to mate. As a result, the entire population on the island has gotten smaller over the past 25 years. Small sheep aren't necessarily a bad thing, but they emphasize the impact of climate change.