While most organisms have biological clocks synchronized with the day-night cycle (circadian rhythms), marine animals in tidal areas have also developed circatidal rhythms to align with the tidal cycle. Comparing the activity and genetic expression of snails from tidal and non-tidal areas, researchers demonstrate that circatidal rhythms develop as snails adapt to tidal environments. These findings highlight the flexibility of biological clocks, enabling organisms to adjust their rhythms according to the environment.