A rod cell marker of nocturnal ancestry.

In a recent Cell article, Solovei et al. (2009) have shown that the rod cell nuclei of nocturnal and diurnal mammals (including primates) are organized in distinct patterns, and that the nocturnalassociated pattern likely facilitates efficient photon capture by the photoreceptors. Their research underscores the exceptional selective pressures placed on the visual system in low light environments and provides a new marker of nocturnal ancestry. This marker can be used to advance our understanding of activity pattern evolution, potentially including the behavioral ecology of ancestral primates.