Nine hundred kilometers off the east coast of Madagascar lies the tiny island paradise of Mauritius. The waters are pristine, the beaches bright white, and the average temperature hovers between 22°C and 28°C (72°F to 82°F) year-round. But conditions there may not have always been so idyllic. A new study suggests that about 4000 years ago, a prolonged drought on the island left many of the native species, such as dodo birds and giant tortoises, dead in a soup of poisonous algae and their own feces. The die-off happened in an area known as Mare aux Songes, which once held...