Yellow-eyed tigers, blue-eyed snow leopards, and other felines may owe their striking iris hues to shared gray-eyed ancestors. The study reporting these findings appeared in a preprint catalogue on bioRxiv.
Within the animal family, the closest living relatives of cats—linsangs, hyenas, and genets—tend to have brown eyes, which suggests a brown-eyed origin for the common ancestor of these lineages. Yet in the cat family, a wider spectrum of eye colors emerged—green, blue, and yellow—millions of years ago, long after those lineages diverged. This diversification hints at dynamic shifts in pigment production over deep time.
In the new research, scientists gathered online photographs of cats to document the eye color across more than 40 species. They then integrated this observational data with a detailed map of evolutionary relationships among living and extinct cats. Using a statistical model, they inferred the likely eye color of the earliest felids at the root of the cat family tree.
The results point to gray and brown eyes as the probable default for the earliest cat ancestors. Eye color is driven by two pigments: eumelanin and pheomelanin. Higher eumelanin produces browns; higher pheomelanin yields yellows. Grays result from moderate levels of both pigments, while blues and greens arise from low levels of both. The researchers propose that an unknown progenitor of all cats carried reduced eumelanin in the eyes due to a random mutation. Over time, additional genetic changes led to the emergence of other colors.
Interestingly, the study did not identify a clear link between eye color and behavior or habitat. This leaves room for the possibility that eye color reflects sexual selection, meaning preferences among potential mates could have steered color variation in felines rather than ecological needs.
Earlier literature has explored a range of ocular topics, including signs of eye health and related conditions. While these studies contribute to a broader understanding of mammalian eye biology, they sit outside the central focus of this evolutionary color work.