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nry David Thoreau. He pares today’s Walden Pond with that of Thoreau’s day. Wilson will use such parisons for the rest of the book. The problem is clean: man has done great damage to his home over the years. Can the earth, with human help, be made to return to biodiversity levels that will be able to support us in the future? Biodiversity, Wilson argues, is the key to settling many problems the earth faces today. Even our agricultural crops can gain advantages from it. A mere hundred species (物種) are the basis of our food supply, of which but twenty carry the load. Wilson suggests changi