"Today, an ancient world is vanishing right before our eyes: the age of giant animals. Over 40,000 years ago, the earth was ruled by megafauna: mammoths and mastodons, saber-toothed tigers and giant sloths. Of course, those creatures no longer exist, and there is only one likely reason for that: the evolution and arrival of the earth's only tool-wielding hunter, the wildly adaptive, comparatively pint-sized human species. Many more of the world's...