PERHAPS YOU RECALL A TIME when you took in more of the world. You were new and the world was new. As a boy, I would go out in the woods and sit under a tree, then lick my thumb and wet each nostril. I had read somewhere that people—perhaps pioneers or American Indians, I don't remember—did this in order to keen their sense of smell for approaching game or danger. I held perfectly still, my back against rough bark, all of my senses waiting. And slowly, animal life returned. A rabbit appeared under a bush, birds swooped low, an ant went on a walk­-about over my knee. I felt intensely alive.

Can we be new again? In 2005, when my book Last Child in the Woods was published, I wasn't prepared for the movement that would follow, and for the reaction of adults when they considered their own lives.

In the book, I introduced the term nature-deficit disorder—not as a medical diagnosis but as a way to describe the growing gap between children and nature. By its broadest interpretation, nature-deficit disorder is an atrophied awareness, a diminished ability to find meaning in the life that surrounds us. When we think of the nature deficit, we usually think of kids spending too much time indoors plugged into an outlet or computer screen. But after the book's publication, I heard adults speak with heartfelt emotion, even anger, about their own sense of loss.

One day after a talk in Seattle, a woman literally grabbed my lapels and said, "Listen to me: adults have nature-deficit disorder, too." She was right, of course. As a species, we are most animated when our days and nights are touched by the natural world. While individuals can find immeasurable joy in a great work of art, or by falling in love, all of life is rooted in nature, and a separation from it desensitizes and diminishes us.

That truth seems obvious to some of us, though it has yet to take root in the wider culture. However, in recent years an emerging body of research has begun to describe the restorative power of time spent in the natural world. Even in small doses, we are learning, exposure to nature can measurably improve our psychological and physical health.

While the study of the relationship between mental acuity, creativity, and time spent outdoors is still a frontier for science, new data suggests that exposure to the living world can even enhance intelligence. At least two factors are involved: first, our senses and sensibilities can be improved by spending time in nature; second, the natural environment seems to stimulate our ability to pay attention, think clearly, and be more creative.

In 2008, for the first time in history, more than half the world's population lived in towns and cities. The traditional ways that humans have experienced nature are vanishing along with biodiversity. At the same time, our culture's faith in technological immersion has no limits. We sink ever deeper into a sea of circuitry. We consume breathtaking accounts of the creation of synthetic life, combining bacteria with human DNA; of microscopic machines designed to enter our bodies to fight biological invaders; of computer-augmented reality. We even hear talk of a posthuman era in which people themselves are optimally enhanced by technology. Aren't we getting a little ahead of ourselves?

By contrast, I believe the future can be shaped by what I call the Nature Principle, which holds that in an age of environmental, economic, and social transformation, the future will belong to the nature-smart—those individuals, businesses, and political leaders who develop a deeper understanding of nature and balance the virtual with the real.