Arlin Stoltzfus is a Fellow of the Institute for Bioscience and Biotechnology Research, and a Research Biologist at the National Institute of Standards and Technology in Gaithersburg, Maryland, USA . He is an evolutionary biologist who uses computer-based approaches to study evolution at the molecular level. His primary interest has been to develop and evaluate theories about evolutionary factors other than natural selection. He and his coworkers proposed the theory of Constructive Neutral Evolution, and showed theoretically that biases in the introduction of variation may impose biases on evolution without requiring neutrality.