The recovery of black-footed ferrets is one of the success stories of conservation biology. Photo by USFWS Mountain-Prairie, used under Creative Commons licensing.It's always a treat to read about a field from one of the people who helped found it. That's exactly what we offer in this week's installment of #ForewordFriday. Michael E. Soulé is one of the founding fathers of conservation biology. In this extract from his new book, Collected Papers of Michael E. Soulé, he shares the conception of conservation biology he developed in 1985. He explains how conservation biology is the crisis side of biology and explores the principles underlying it.