【英语时差8,16】进化在行动（在线收听）

Evolution In Action Although rainforests cover less than two percent of Earth’s surface, they are home to more than half of all plant and animal species. How did rainforestsevolve so much more diversity than other parts of the globe? For starters, tropical species have had longer to evolve without extreme challenge from things like glaciers. Instead of destroying rainforests, climate changes like the ice ages usually just cause them to shrink. As a matter of fact, this periodic shrinkage might actually help generate more new species than it kills off.This is how it happens. When a rainforest shrinks, it sometimes fragments into isolated rainforest pockets. These pockets can stay separated long enough for the isolated plants and animals to begin developing into different species from their cousins next door. When the pockets grow back to form a single forest again, the forest can have twice the number of species that it started with. Scientists working in the Daintree and Atherton Tableland rainforests of Australia have uncovered strong evidence for this. These rainforests are connected now, but during ice ages they were separated by a dry area. The scientists studied the genes of birds and lizards living on opposite sides of this area. Almost all the bird species showed a significant amount of genetic difference. What’s more, scientists found that the genes of one lizard species–the prickly skink–were so different that these skink are well on their way to becoming two separate species. We usually think of climate disasters like ice ages as bad news for life everywhere. In rainforests however, they can be an engine which, over time, enriches the web of life on Earth.