As the nature deficit grows, another emerging body of scientific evidence indicates that direct exposure to nature is essential for physical and emotional health. For example, new studies suggest that exposure to nature may reduce the symptoms of Attention Deficit Hyperactivity Disorder (ADHD), and that it can improve all children's cognitive abilities and resistance to negative stresses and depression.

Today's children are living a childhood of firsts. They are the first daycare generation; the first truly multicultural generation; the first generation to grow up in the electronic bubble, the environment defined by computers and new forms of television; the first post-sexual revolution generation; the first generation for which nature is more abstraction than reality; the first generation to grow up in new kinds of dispersed, deconcentrated cities, not quite urban, rural, or suburban.

A natural environment is far more complex than any playing field.

In medieval times, if someone displayed the symptoms we now identify as boredom, that person was thought to be committing something called acedia, a 'dangerous form of spiritual alienation' -- a devaluing of the world and its creator.

This seems clear enough: When truly present in nature, we do use all our senses at the same time, which is the optimum state of learning.

In our bones we need the natural curves of hills, the scent of chaparral, the whisper of pines, the possibility of wildness.

What if a tree fell in the forest and no one knew it's biological name? Did it exist?