Comment on "Divergent induced responses to an invasive predator in marine mussel populations".

Freeman and Byers (Reports, 11 August 2006, p. 831) presented evidence for the rapid evolution of antipredator defenses in the mussel Mytilus edulis. However, their analysis is confounded by three issues. Samples from some sites are likely to have included a second species, M. trossulus; their manipulation of chemical cues does not preclude other interpretations; and they failed to establish an adaptive significance to shell thickening.