In Science this week, an international team led by investigators at the University of Houston report the effects of epistatic interactions among mutations on fitness "for the first five mutations to fix in an experimental population of Escherichia coli." The team says that "epistasis depended on the effects of the combined mutations," such that "the larger the expected benefit, the more negative the epistatic effect." As a result, the team says that in its study, epistasis "tended to produc