eLife Assessment
This important report describes the changing antiviral activity of IFIT1 across mammals and in response to distinct viruses, likely as a result of past arms races. One of the main strengths of the manuscript is the breadth of mammalian IFIT1 orthologs and viruses that were tested, as well as the thoroughness of the positive selection analysis. Overall the evidence is convincing, and the discussion conveys well the limitations due to physical interactions with other IFITs that are not accounted for.