Shakespeare wrote in his tragic play Macbeth that slumber is a “Balm of hurt minds” and “Chief nourisher in life's feast.” In this issue's cover story, sleep researcher Robert Stickgold explains the many ways those statements are far more than pretty turns of phrase. In fact, it is physiologically vital that we spend about a third of our lives unconscious.

Dozing, Stickgold writes, is involved in a “multitude of biological processes—from the inner workings of the immune system to proper hormonal balance, to emotional and psychiatric health, to learning and memory, to the clearance of toxins from the brain.” Losing a few hours of shut-eye depresses various functions, reducing our cognitive and memory powers, souring our mood, even reducing our body's ability to defend against infections. If we did not snooze at all, eventually we would die. Click here to learn more about our remarkably restorative nightly visits to the land of Nod.

It has taken decades to develop even a rough understanding of the multiple benefits of catching 40 winks, but the weight of ongoing studies eventually has made the picture clearer. The clarifying effect of the gradual accumulation of data is a steady theme in the evolution of modern research in general and forms the underpinning of this year's “State of the World's Science” special report, organized by Fred Guterl, with editing support from Seth Fletcher and Mark Fischetti and graphic design by Jen Christiansen.

Data are the fuel for the engine known as Big Science—those bold projects that aim to tackle challenging large questions and to help make progress on some of humanity's toughest problems. In “Trouble in Mind,” for instance, journalist Stefan Theil looks at how researchers are trying to pry the operational secrets from the biological computing machines in our skulls. The uneven success to date of vast brain research projects in the European Union, the U.S. and elsewhere shows just how difficult managing large-scale efforts can be. Next, Dean Karlan asks in “More Evidence, Less Poverty,” do microloans really help the world's poorest? The answer will surprise you. In “An Antidote to Murder,” Rodrigo Guerrero Velasco describes his experiences as mayor of Cali, Colombia, where he used data to address an epidemic of violent homicides—with compelling results. And through the Nature Index, we showcase the top research institutions around the world; see “World Leaders,” (Scientific American is part of Springer Nature.)

The process of science can't solve all the world's problems, of course, but it is often deeply inspiring to me to realize how much it can help.