In public estimation, sloths have undergone an astonishing transformation in the course of the past few years. Thanks largely to YouTube clips posted by the sloth orphanage in Costa Rica, sloths have attracted a vast audience of admirers. Instead of seeing them as ridiculous anachronisms of which we know little, they have turned into creatures considered by many to be the most endearing on earth. Over much the same period, scientific investigations have also changed our view of sloths. No longer are they seen as total misfits in the modern world but, in the words of one specialist sloth investigator, they are "masters of an alternative lifestyle." This wonderfully entertaining book reveals the fascinating history of the sloth, from the prehistoric ground sloth to modern pygmy sloths in Panama, explores the current state of the science of sloths, and reveals the truth behind sloth behavior.

A playful and diverting, yet always scientifically rigorous look at those simple mysteries that are yet to be solved Why are so many giraffes gay? Has human evolution stopped? Where did our alphabet come from? Can robots become self-aware? Can lobsters recognize other lobsters by sight? What goes on inside a black hole? Are cell phones bad for us? Why can't we remember anything from our earliest years? Full of the mysteries of life, the universe, and everything, this is a fascinating and unputdownable exploration of the limits of human knowledge of our planet, its history and culture, and the universe beyond.

There are many, many more things that nobody knows. Do animals have a sense of humor? Why do we have five fingers? How long can humans live? What did Jesus do in his youth? Which speech did Lincoln deliver at Gettysburg? Does the appendix have any use? Is there an odd perfect number? In this witty and enlightening follow-up to The Things that Nobody Know s, William Hartston takes us on a guided tour of 501 further gaps in our knowledge of cosmology, mathematics, animal behavior, medical science, music, art, and literature.