National Geographic: It's hard to be an optimist these days. We are living through what biologists call the sixth mass extinction, a time of dramatic depletion of species, from frogs to rhinos and butterflies. By the end of the century, it is estimated that one in six species will be extinct. The causes-human population growth, habitat loss, climate change-are complex and interlocking, fueling each other in an ever faster destructive spiral.
But E.O. Wilson, the esteemed biologist and National Geographic Hubbard Award...