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========== Earth's ecosystems have always been changing,
with species mixing and mingling thanks to migrations, freak events, and slow creeping
expansions. But since we humans arrived on the scene, we've put things into fast-forward,
moving plants, animals, and other organisms around the globe -- whether intentionally
or not. Once in a while, one of these transplants
might have an evolutionary quirk -- like deadly poison, a lack of predators, or a voracious
appetite -- that unexpectedly helps it dominate its new territory. Earthworms, for example,
were introduced into North America by European settlers and have been inching across the continent
ever since - tilling soil and improving crop yields as they go. But if a newcomer starts to harm us or a part...