LiveScience: The saber-toothed cat, large ground sloth and other ice age giants of South America didn't go extinct solely because of climate change or prehistoric human activity, but because of a perfect storm of the two that hit the giant beasts at the same time, a new study finds. For years, researchers have debated what felled many of the megafauna animals that weigh more than 100 lbs. (45 kilograms) shortly after the end of the last ice age. Some scientists blamed humans, who had newly colonized the...