The European blackcap, above, is evolving in response to climate change. Shorter and milder winters are allowing more blackcaps to overwinter in Britain rather than on the Iberian Peninsula. These British birds mate only with each other and are becoming genetically distinct from the larger population--the possible beginnings of a speciation event. The blackcap is one of many animals expressing heritable genetic changes as a result of altered seasonal events, including other birds, squirrels and mosquitos. The evolution of these species is being driven by changes in the timing of the seasons or in season length, rather than simply warmer temperatures. The mounting evidence for climate change-induced evolution is discussed in an article in the perspectives section of this week's Science.