Most natural populations experience extremely stressful conditions. This book discusses how such conditions can cause periods of intense selection that increase both phenotypic and genetic variation, and allow organisms with novel characteristics to be first generated and then established in the population. Using evidence from the fossil record, the authors argue that stressful conditions can have a major impact on the environments. They also suggest that as a consequence, periods of stress must be taken into consideration when long term conservation strategies are planned, particularly as stressful conditions emerge as a result of human activities. This broad overview will be of great interest to students and researchers in the field of evolutionary biology, genetics, ecology, paleontology and conservation biology.