Eye Color
- Lafyva
- May 31, 2019
- 6 min read
Updated: 51 minutes ago
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.
AI Overview
That's correct. HERC2 and OCA2 are not examples of disassortative mating. Instead, they are distinct genes that work together to influence eye color. HERC2 regulates the activity of OCA2, which produces the pigment melanin, resulting in the variation of eye colors.
Here's a more detailed explanation:
OCA2 (Oculocutaneous Albinism II):
This gene is a major player in determining eye color, specifically the amount of melanin produced in the iris.
HERC2 (HECT and RLD domain containing E3 ubiquitin protein ligase 2):
This gene interacts with OCA2 and acts as a regulator, influencing how much pigment OCA2 produces. A specific variant in HERC2 is linked to blue eye color.
Interaction:
The HERC2 gene contains a region that acts as an enhancer for the OCA2 gene, meaning it controls how much OCA2 protein is made. Variations in this region of HERC2 can affect how strongly the enhancer acts on OCA2, leading to different amounts of melanin and thus different eye colors.
Disassortative mating refers to the preference for individuals with different traits in a mate, which is not what's happening with HERC2 and OCA2. These genes are involved in the biological process of pigmentation, not mate selection.
For a more helpful explanation to your audience, you could say: "While HERC2 and OCA2 are both involved in eye color, they don't determine who we mate with. They are genes that work together to produce the different shades of brown, blue, or green we see in our eyes".
AI Overview
That's correct. HERC2 and OCA2 are not alleles at different loci on the same chromosome; instead, they are two distinct genes that interact to influence eye color. Specifically, HERC2 regulates the expression of OCA2, which is the primary gene responsible for melanin production in the iris. While they are located near each other on chromosome 15, they are not different forms of the same gene. Furthermore, they are not in linkage disequilibrium (LD); their variations are inherited together at a much higher rate than would be expected by chance, indicating a functional relationship rather than just physical proximity.
Here's a more detailed explanation:
Not alleles at different loci:
Alleles are different versions of the same gene, found at the same location (locus) on a chromosome. HERC2 and OCA2 are different genes, each with its own set of alleles.
Functional interaction:
HERC2 plays a crucial role in regulating the expression of the OCA2 gene. Specific variations in HERC2 can impact how much melanin OCA2 produces, affecting eye color.
Not in LD:
Linkage disequilibrium refers to the tendency of certain gene variants to be inherited together more often than would be expected by chance. While HERC2 and OCA2 are located close together on the chromosome and variations in these genes are often inherited together, they are not in LD because their close proximity is not the sole reason for their correlated inheritance. The functional relationship, where HERC2 regulates OCA2, explains why their variations are frequently inherited together.
Melanin and Eye Color:
The amount of melanin produced by melanocytes in the iris determines eye color. OCA2 encodes a protein called the P protein, which is involved in melanin production. HERC2 influences the amount of P protein produced, thus affecting eye color.
