Darwinian evolution is a robustly supported scientific theory. Yet creationists continue to challenge its teaching in American public schools. Biology teachers in all 50 states are responsible for teaching science content standards that include evolution. As products of their backgrounds and affiliations teachers bring personal attitudes and beliefs to their teaching. The purpose of this study was to explore how biology teachers perceive, describe, and value their teaching of evolution. This research question was explored through a heuristic qualitative methodology. Eight veteran California high school biology teachers were queried as to their beliefs, perceptions, experiences and practices of teaching evolution. Both personal and professional documents were collected. Data was presented in the form of biographical essays that highlight teachers' backgrounds, experiences, perspectives and practices of teaching evolution. Of special interest was how they describe pressure over teaching evolution during a decade of standards and No Child Left Behind high-stakes testing mandates. Five common themes emerged. Standards have increased the overall "amount" of evolution that is taught. High-stakes testing has decreased the "depth" at which evolution is taught. Teacher belief systems strongly influence "how" evolution is taught. Fear of creationist challenges effect evolution teaching strategies. And lastly, concern over the potential effects of teaching evolution on student worldviews was mixed. Three categories of teacher concern over the potential impact of evolution on student worldviews were identified: Concerned, Strategist, and Carefree. In the final analysis teacher beliefs and attitudes still appeared to he the most important factor influencing how evolution is taught. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]