Eye Color
- Lafyva
- May 31, 2019
- 4 min read
Updated: Nov 24, 2025
After comparing eye color information to behavioral information, it seems to me that the pattern holds across all classes of land vertebrates. One can see this by looking, first, at birds and bats. It is only the darkest-eyed families (mostly comprised of species with black or dark brown iris colors) that specialize in feeding on the wing in an open environment. That behavior is very dependent on speed and quick reactions. At the human level, that is analogous to outfielders in baseball; they, too, must have the speed, quick reactions, and developed skills to catch flies in an open environment. At the other extreme, lightest-eyed, one finds herons. Their eye colors are mostly not dark at all, but yellowish, as are the eyes of families of frogs, cats, geckos and vipers. (These are the lightest-eyed large families in our database and come from all four classes of land vertebrates.) These animals are all hunters that lie-in-wait or slowly stalk prey before a sudden strike or pounce. All have some form of spring-loaded anatomy, such as folded neck, coiled tongue, or coiled body, that aids in making a sudden strike. At the human level, this is somewhat analogous to a slow-running quarterback in American football who, nevertheless, manages to be successful because of his ability and developed skill to just wait, with cocked arm, in a “pocket” of blockers, until the right moment to make a sudden strike downfield to an open receiver. Waiting, good timing and sudden release are all critical elements in the sequence. It is easy enough to see in nature that yellow-eyed predators and black-eyed predators differ. Yellow-eyed predators use a tactic of WAIT WITHOUT MOVING. Black-eyed predators, such as those that feed on the wing, rely on a tactic of MOVE WITHOUT WAITING. Animals with eye darkness in the midrange between yellowish colors and dark brown or black (blue, green, gray, orange, red, hazel, light brown, brown) tend not to be skilled hunters, but, rather, rely more on finding immobile food (e.g. fruit, carrion, grubs, grass, eggs, ants, spiders). I have characterized this behavior as self-paced, or CAN WAIT. At least on the timing dimension, this is analogous in human sports to activities that are self-paced, such as pitching in baseball, shooting free throws in basketball, and the sports of golf and bowling. [Land vertebrates that can hunt in total darkness tend to be dark-eyed and rely heavily on KEEN senses other than vision-such as hearing (e.g. Barn owls), touch (e.g. Boat-billed heron) or smell (e.g. pittas).] To make sure that I was not “cherry-picking” my observations, I had twenty-one ornithologists make blind ratings of quick-versus-deliberate behavior for large families of birds. Those ratings confirmed that, in birds, controlling for differences in size, light eyes were associated with deliberate behavior and dark eyes were associated with quick behavior. Herons were rated as most deliberate and swifts received the highest ratings for quickness. In addition to being very cat-like in hunting behavior, some herons rely on passive, MUST WAIT, defense. They use their streaked coloration to hide in reed beds with their bills pointed straight up. In contrast, swifts are very aerial and sometimes spend years aloft without landing. They use flight speed of almost 200 miles an hour and active, MUST NOT WAIT, reactions as their primary method of defense. One implication of the above information is that a skilled predator will very often have an eye color that is yellowish or dark brown/black. However, the fact that a species has yellow or black eyes does not indicate that it is a skilled predator because many herbivores or omnivores have these eye colors also. The important thing to remember is that if the animal is a predator, knowing its eye color will allow you to predict its hunting strategy. The pattern of eye color and behavior in land vertebrates is given in more detail in an earlier book, Animal Eye Colors: Yellow-eyed Stalkers, Red-eyed Skulkers & Black-eyed Speedsters. Descriptive statistics and brief analyses of differences between taxonomic families (within each order) are given for all orders of land vertebrates for which we have sufficient information on species eye colors. Included are analyses for two orders of amphibians, three orders of reptiles, five orders of mammals, and 15 orders of birds. The consistency across all four classes of land vertebrates demonstrates the general nature of the phenomenon.
Worthy, Morgan. I Have Known the Eyes Already . Kindle Edition.
MFJ: What about the physiological links between eye color and behavior? MW: I deal with the externals and not the internals. However, if you want to explore the internals I can tell you enough to get you started. Amount of melanin in the iris is correlated with amount of melanin in the inner ear (Bonnaccorsi 1965) and with amount or distribution of neuromelanin in the central nervous system (Happy and Collins 1972). In terms of the link to motor behavior, it is perhaps significant that neuromelanin can function as a semiconductor (McGinness et al. 1974). Eye color is polygenic and the specific genetic causes are still being sorted out (Zhu et al. 2004). I just use eye color or eye darkness as a marker variable that is external and easily observed. In fact, eye color was used as a marker variable in many of the early studies of genetics.
I HAVE KNOWN THE EYES ALREADY A Research Memoir Morgan Worthy
Speed/Accuracy Trade-Off between the Habitual and the Goal-Directed Processes
"Another influential factor that seems to favour habitual decisions despite their non-optimality is that goal-directed deliberation consumes more energy than habitual action selection. For example, low availability of blood glucose, which is the main fuel supporting brain function, results in impairments in cognitive tasks [72]. This factor can be captured by
adding an energy cost term, C (Cw0), to the cost of deliberation, and hence, for arbitration between the two processes, the VPI signal must be compared with CzR t."
Nettle(2006) argues that whilst it is difficult for us to comprehend, high levels of Agreeableness does not often lead to an adaptive strategy. For example, those who are prone to unconditional trust (high level of Agreeableness) are likely to be out competed by others (e.g. Trivers 1971; Axelrod and Hamilton 1981; Maynard-Smith 1982).
Associations between iris characteristics and personality in adulthood
The retina contains two types of photo receptors, rods and cones. The rods are more numerous, and are more sensitive than the cones. However, they are not sensitive to color.
