The third in our occasional series on the ecological sciences looks at biodiversity and the extinction of species. What is biodiversity and why is it important? What do the numbers tell us about how much of it we’re losing and why? Answering these and other question is Dr. Peter Raven, an active member of the Pontifical Academy of Sciences and one of the world’s leading botanists and advocates of conservation and biodiversity. Described by Time magazine as a “Hero for the Planet,” Dr. Raven champions research around the world to preserve endangered plants and is a leading advocate for conservation and a sustainable environment.