Children have believed the legend forever: On one evening each year a jolly old elf and eight reindeer fly all night long to deliver gifts around the world. The fact is, solid evidence abounds. Robert Sullivan, a senior editor at Life magazine, diligently gathered documentation from scientists, historians, zoologists, and Arctic explorers to prove that Santa is not just a myth. First, the reindeer: Do they really fly? "We used to think it was just...