Andrew Balmford of the University of Cambridge and his colleagues looked at case studies of the economic productivity of ecosystems before and after they were converted to human use. They found that in each case the value of the wild land far outweighed that of its altered counterpart. In fact, the team estimates that global conservation of the natural habitats that remain would have an overall benefit to cost ratio of at least 100 to 1.

"People are hearing a message that nature is being eroded, but it takes a while to sink in, even for me," Balmford remarks. "One third of the world's wild nature has been lost since I was a child and first heard the word 'conservation'--that's what keeps me awake at night."