Scientists working on eScience environments use workflows to carry out their experiments. Since the workflows evolve as the research itself evolves, these workflows are a good tool to track the evolution of the research. Scientists can trace their research and associated results through time or even go back in time to a previous stage and fork to a new branch of research. In this paper we introduce the workflow evolution framework (EVF), which is implemented in the Trident workflow workbench. The primary contributions of the EVF include i) management of knowledge associated with workflow evolution and ii) enabling reproducible research. Since we believe evolution can be used for workflow attribution, our framework will encourage researchers to share their workflows and get the credit for their contributions.