While humans and many land animals possess eyelashes for eye protection, sharks do not. These aquatic predators have evolved distinct and highly specialized adaptations suited for their underwater environment, which negate the need for such features.
Anatomy Without Eyelashes
Eyelashes in terrestrial animals primarily shield eyes from airborne particles like dust, debris, and sweat. They also help spread tear film and maintain lubrication. In a marine environment, these functions are not necessary; continuous water flow over a shark’s eyes provides natural lubrication and cleaning, washing away irritants. Constant immersion removes the evolutionary pressure for sharks to develop eyelashes. Given their environment, eyelashes would offer no practical benefit and could even become a hindrance, potentially trapping small particles or creating drag.
Specialized Eye Protection
Despite lacking eyelashes, sharks possess sophisticated mechanisms to safeguard their eyes. Many shark species utilize a nictitating membrane, or “third eyelid.” This translucent or opaque membrane rapidly slides across the eye, providing a protective shield during aggressive encounters, feeding, or when navigating abrasive environments. For example, a tiger shark closes this membrane when attacking prey to prevent injury from struggling animals.
Some shark species, including the great white shark, do not possess a nictitating membrane. Instead, they protect their eyes by rolling them backward into their sockets, exposing a tough area. This “eye-roll” occurs just before or during an impact, such as when biting prey, guarding the delicate eye from sharp teeth, claws, or bone fragments. The shark’s cornea is also tough, contributing to the resilience of their eyes in a high-pressure aquatic environment.
The Role of Shark Vision
Shark eyes are specialized for underwater conditions, allowing them to navigate and hunt. Their visual systems excel in low-light environments, enhanced by a reflective layer behind the retina called the tapetum lucidum. This tissue reflects light back through the retina, improving their ability to see in dim or murky waters, similar to cat night vision. Some shark species can see an object’s contrast against the background rather than color.
While vision is important, sharks do not rely on it exclusively. They possess other senses that work with sight for hunting and navigation. These include a keen sense of smell, detecting traces of substances in the water over long distances. Their lateral line system detects water movement and vibrations, and the ampullae of Lorenzini detect electrical fields produced by living organisms, even those buried in sand. This multi-sensory approach ensures sharks remain effective predators, even without eyelashes.