2.5-minute read
One aspect of this lockdown situation that we hadn’t anticipated, out of a long list of things that we hadn’t anticipated, because we’ve never done this before, was the staring. The uninterrupted (except by naps), somewhat guilt-inducing house cat staring. Since we’ve been “inside,” we can’t shake the feeling that we’re being watched—and that’s because we are. Watched from the bookshelves, watched from the windowsill—from the stairs, from the hallway, from inside the closet. Those innocent gold-green eyes track our every move and seem to be saying, “We’ve noticed that you are here all of the time now. Since you are here all of the time now—umm, more food?”
The cat staring got us thinking about eyes in general and pupils of eyes in particular and why cat pupils are shaped differently than human pupils. As it turns out, pupil shape is primarily a function of the predator-prey relationship—whether a species hunts or is hunted, is an herbivore or a carnivore, and what time of day it’s active. Through evolutionary adaptation, animals have developed optical superpowers that will maximize the odds of finding food or minimize the odds of becoming food.
According to researchers at UC Berkeley, ambush predators like house cats, tigers, and crocodiles that are either nocturnal or hunt both during day and night are highly likely to have vertically slit or vertically elongated pupils. Animals more likely to become prey like sheep, horses, and goats tend to have horizontally elongated pupils. Pupil shape is an adaptation that increases survival in the environment where a species evolved. Vertically elongated pupils give ambush predators laser-sharp focus on vertical shapes and greater perception of depth and distance so they can choose the ideal path to their next meal. The horizontally elongated pupils of prey species enable them to have a nearly panoramic view ahead and behind to detect approaching predators and make a quick getaway. Both vertically and horizontally slit pupils can expand up to 300 times for better vision in low light.
The location of eyes on an animal’s head also determines how they perceive depth and distance. Ambush predators with frontally-placed eyes like cats and tigers combine visual information from both eyes to home in on their target. Scientists believe some prey animals with lateral eyes that don’t have overlapping fields of view, including pigeons, quails, and doves, bob their heads to visually perceive their environment. However, head movement in ambush predators with lateral eyes like crocodiles would give away their position and potentially cost them their lunch. To compensate, their eyes have a structural advantage that projects images through different parts of the pupil, allowing them to better focus on prey.
Interestingly, height is also a factor in pupil shape. The UC Berkeley study found that in general, the taller the predator, the more rounded the vertically elongated pupils, which is why tiger pupils are closer to oval, and low-lying crocodiles have pupils that are vertical slits.
Bottom line, should you ever find yourself to be an object of intense interest for a wild one with vertically slit pupils, consider proceeding immediately to extreme social distancing.
And what about the vertically slit pupils of the staring house cat then? Well, even if you’re an indoor, purr-prone, domesticated descendant of wildcat predators and your prey comes out of a can and that can has to be opened by non-prey with opposable thumbs—evolutionary optical adaptations still dictate that you keep your eyes on the purveyor of the prize.
