If you are out in the yard with your pet, Morgan Worthy explains (in I Have Known the Eyes Already), and it sees a squirrel nearby, what it does next will probably depend on whether your pet is a cat or a dog:
The immediate response of a cat is to freeze, then crouch and start to stalk in preparation for an ambush. The immediate response of most dogs is to run, without delay, toward the squirrel and chase it. One is a stalker; the other is a chaser and uses immediate, direct pursuit. The first responses of cats and most dogs on sighting prey are very different from each other. Only after the prey has come close to the waiting cat or the cat has slowly worked its way close to the prey, does the cat suddenly pounce.
The typical dog makes quick moves; the cat makes sudden moves. Understanding the difference between those two words, quick and sudden, is necessary to understand everything else we will talk about. Quick implies an immediate reaction; sudden implies an abrupt move after some delay. The origins of the two words make this plain. “Quick” means “swift, lively.” “Sudden” means literally “to approach secretly” and comes from two Latin words that mean “secretly” and “to go.” One way to remember it is immediate quick and delayed sudden.
Another way to state this is that one is quick and the other is deliberate. If we can agree that most dogs tend to be quick and most cats tend to be deliberate, we can then move on to differences in eye darkness between the two. The reactivity hypothesis is that dark eyes are associated with quick responses and light eyes are associated with deliberate responses. Using our example, we can predict that dogs are darker-eyed than cats. A simple way to get a measure of eye darkness is to say that only brown eyes and black eyes are considered dark and all others are considered light.
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Dogs tend to be significantly darker-eyed than cats. Of the 27 breeds of domestic cat, none are dark-eyed. They are all in the range of yellow-amber-orange-blue-green. None are at the other end of the scale—black, dark brown, brown—that we are treating as dark-eyed. The same is true for cats in the wild. Look with me here at the database (Worthy 2000, p44). In the wildlife literature we found eye colors for 15 species of cat. All had yellow or yellowish eyes except for one, the Ocelot, and its eyes are reddish brown. So, for 27 breeds of domestic cat and 15 species of cats in the wild, using our 2-point scale of eye darkness, every one of them gets a score of 0.
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Most dogs react to prey by immediately giving chase. One group of dogs, though, employ an initial response to prey that is very much like the initial response of cats. Pointers and setters, like cats, freeze when they first sense prey nearby. Pointers adopt a standing pose and setters crouch. In regards to this initial response, I think any fair observer would grant that pointers and setters are more deliberate or cat-like than are other dogs. If the reactivity hypothesis is correct, those breeds (all are often just referred to as Pointers) should be less likely than other breeds to have dark eyes. That is, indeed, the case. Whereas 70% of other breeds are dark-eyed, only 28% of the pointer or setter breeds are dark-eyed. A difference that large, given the sample sizes, could occur by chance less than one time in a thousand.
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Pointers are bred for “freezing” as first response to prey; hounds are bred to track and chase prey; terriers are bred for not only chasing the prey, but for following it into burrow or den—which requires a high level of persistence and courage. Simon & Shuster’s Guide to Dogs (Pugnetti 1980) uses a symbol to indicate adaptation for each of those three behaviors.
There is a progression. Fifty-five per cent of pointer breeds have yellowish eyes; for hounds, it is only 10%, and there is no breed of terrier that has yellowish eyes. Yellow eyes seem to be associated with hesitation or freezing behavior, which is good for animals that stalk. Hesitation would tend to be a liability for animals that hunt by means of direct pursuit. And that would be especially true for terriers, which are expected to pursue the prey into its den.
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Dark-eyed animals show active courage; light-eyed animals that freeze when predators are near show passive courage.
One of the main things to remember, though, from our talking about cats and dogs, is that predators that depend a lot on freezing, ambush, lying-in-wait, stalking, or any other form of surprise to take prey will not only be light-eyed, but most likely will have yellowish eyes. I know we have only covered three examples so far—domestic cats, cats in the wild, and dogs that point or set—but the same pattern is seen with all classes of land vertebrates. Any type predator that uses surprise to ambush prey (in less than total darkness) tends to have yellowish eyes. That can be noted by anyone who cares to look within various orders or sub-orders of animals: frogs, snakes, lizards, crocodilians, carnivores, primates, raptors, owls, heron-like birds, and various other orders of birds.
No one can deny that statement, but they can ignore it. Given human history, people of good will are now reluctant to acknowledge any evidence that pigmentation can be related to behavior. We seem always to go from one extreme to the other.
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Helen Mahut (1958) did a study in Canada in which she compared ten breeds of dog on response to novel stimuli and categorized the behavior as “fearless” or “fearful,” depending on how bold or inhibited the dogs were in their responses. I no longer remember the particular breeds, but when I checked the eye colors, the most fearless dogs were also the ones with the darkest eyes.
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Asdell (1966) described wolves as being cautious, cowardly and fearful of novel stimuli. They pursue prey in a circling or zigzag manner in order to set up an ambush. That is not direct pursuit as is seen in terriers or weasels. Nor is it as non-reactive as the behavior of cats and pointers. Because wolves are lighter eyed than most dogs it is significant that Asdell also reported that wolf-dog hybrids exhibit “passive defense reactions” more than do most dogs.
I’ve got to express my gratitude for you bringing this thesis to my attention. It’s fairly rare that I come into contact with a macro biological or physiological concept that I’ve never heard about before and seems novel and intriguing. I’m not yet totally sold on the theory, but there’s enough even in these excerpts to make it seem plausible at the very least.
Like Handle said. This is great stuff.
So Blue-eyed devils are the best ambush hunters, black-eyed demons are the best chase hunters, and to my blooshot hazel eyes it looks like the inbetween eye colors are for skulking, carrion eating bad hunters. Worthy does say that skulkers are a little smarter than the other two, because we have to overcome our crap hunting incapacities.
Bram Stoker’s vampires are red-eyed skulkers.
I’m glad you’re enjoying Morgan Worthy’s eye-color hypothesis, Bruce and Handle — and I’ll definitely keep my eyes peeled for any red-eyed skulkers.