Evolutionary advantage often makes for show-stopping stuff--a cheetah's speed, for example, or a moth's almost perfect mimicry of tree bark. In some snails, however, it's simply down to a poor fit ...

Knocking out one gene in the snail Lymnaea stagnalis reverses shell coiling. In contrast to the wild-type dextral snail (right), a CRISPR-created snail shows sinistral coiling (left). Disclaimer: AAAS ...