In nocturnal mammals, which photoreceptor type is more abundant?

• A. More cones than rods
• B. More rods than cones
• C. Equal numbers
• D. No rods exist

Answer: (B)

Rod-dominant retinas optimize vision in low light. Rods are extremely sensitive to small amounts of light and can detect single photons, which helps nocturnal mammals see in dim conditions. Cones, on the other hand, require brighter light and provide color vision and fine detail, which isn’t as useful at night. As a result, nocturnal species have many more rods than cones, boosting night-time sensitivity even though color and sharpness are sacrificed. If there were more cones or equal numbers, night vision would be poorer; having no rods would leave the animal unable to detect faint light at all.