COSMOLOGY18 Does the Multiverse Really Exist? The answer could be unknowable. By George F. R. EllisHUMAN ORIGINS24 The Evolution of Grandparents Senior citizens may have been the secret of our species’ success. By Rachel CaspariNEUROSCIENCE30 How to Build a Better Learner Brain studies suggest new ways to improve reading, writing, arithmetic—and even social skills. By Gary StixENERGY38 The False Promise of Biofuels They were to save us from our dependence on oil, but the breakthroughs are not forthcoming. By David BielloLIFE SCIENCE46 Treasure in the Trees Birds’ nests offer clues about natural history, climate change and their owners’ mating habits. By Nina BaiMEDICINE48 A Breath of Fresh Air Fundamental understanding of basic biology has set the stage for new treatments for cystic fibrosis. By Steven M. Rowe, J. P. Clancy and Eric J. SorscherSOCIOLOGY54 How New York Beat Crime The Big Apple has rewritten the rules on fighting homicides, muggings and other urban ills. By Franklin E. ZimringPHILOSOPHY OF SCIENCE60 Why Math Works The answer turns on knowing whether math is invented or discovered. By Mario LivioARCHAEOLOGY64 Guardian of the Pharoahs Egypt’s minister of antiquities has a personal history every bit as tumultuous as his country’s recent past. Interview by Jeffrey Bartholet