How early mammals evolved night vision to avoid predators
Cell Press
To investigate the origin of rods in mammals, Swaroop and his team examined rod and cone cells taken from mice at different stages of development. A majority of the photoreceptors (97%) in the retina are rods (black). Credit: Jung-Woong Kim The researchers saw that in early stages, two days after the mice were born, developing rod cells expressed genes normally seen in mature short-wavelength cones (which are used in other animals to detect ultraviolet light). (Counter-intuitively, humans depend more on cones for our vision, but that’s because our ancestors later evolved to take advantage of the daylight hours again.) The evolution of rod-dominant retinas was a critical adaptation, allowing mammalian ancestors to survive a nocturnal bottleneck.