Two recent studies in BMC Biology and Evolution raise important
questions about a textbook case of frequency-dependent selection
in scale-eating cichlid fishes. They also suggest a fascinating
new line of research testing the effects of handed behavior on
morphological asymmetry. The twisted smiles of left- and right-
bending scale-eating cichlids (Figure 1) have achieved near-
legendary status among evolutionary biologists since their
explosion onto the scene in 1993 . As more data have
accumulated, though, the story has become both more interesting
and decidedly more puzzling. Two recent papers, by Stewart and
Albertson in BMC Biology  and Van Dooren et al. in Evolution ,
add valuable new perspectives, including the exciting
possibility that handed behavior may amplify mouth asymmetry
during growth. But these and other studies also raise important
questions about this textbook case of frequency-dependent
selection. Figure 1. Conspicuously asymmetrical left-bending
(left) and right-bending (right) individuals