While most wild animals have a very limited range of eye colors (usually black, brown, and yellow), wild cats have strikingly colorful eyes.
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According to experts, tracing the evolution of eye color in a species is quite challenging, mainly because fossils do not preserve it, taxidermy specimens have artificially crafted eyes, and most books illustrate only one example per species.
However, scientists have now taken advantage of the abundant photographs of wild cats available online to map the transition from brown eyes to colors such as green and blue, and they were able to identify a gray area in between.
First and foremost, it is important to note that the eye color of any animal is determined by its levels of eumelanin, which makes the eye brown-black, and pheomelanin, which makes the eye red-yellow.
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With this in mind, it becomes easier to understand that eye colors vary depending on the amounts of each pigment, with different combinations leading to colors such as blue, green, and gray.
For a paper in iScience, Harvard University biology graduate student Julius Tabin and his co-author, Katherine Chiasson, used a process called “ancestral state reconstruction” to determine the eye colors of extinct wild feline species based on those of their living descendants.
The authors analyzed the clearest images submitted to the iNaturalist.org database, classified the eye color of each cat, and mapped the data onto the feline family tree using an algorithm to determine the possible eye colors of each common ancestor.
The algorithm considered the likelihood of certain changes and calculated the time since species diverged to generate the most probable colors at each split. When an eye with moderate amounts of eumelanin and pheomelanin appeared, producing gray eyes, blue and green were not far behind.
Next, they tried to correlate this information with factors such as habitat, skin color, and hunting behavior to help explain why these shades evolved, but they found no correlation.
Tabin explained that “huskies have these bright blue eyes because we wanted them to” and bred them accordingly, but in wild cats, “I have no idea what’s going on here.”
It would be plausible to consider that reproductive selection played a role—that is, that cats may have chosen mates with specific eye colors to reproduce—but testing this hypothesis would be difficult.
Ultimately, eye color is “a very overlooked trait, and that’s a shame because it’s probably ecologically and evolutionarily important,” explained evolutionary biologist Arianna Passarotto of the University of Glasgow to Scientific American.
However, Passarotto, who was not involved in the study, expressed skepticism about using photos taken under uncontrolled conditions but described the study as “ambitious” and “absolutely very innovative.”
Photos: Pexels. This content was created with AI assistance and reviewed by the editorial team.
