In 1992, in Burlington County, Ontario, photographer Scott Gardner captured an image that would become one of the most enduring puzzles in herpetology (the study of amphibians).
The photograph, later published in The Hamilton Spectator, showed an American Toad (Bufo americanus) with a seemingly impossible biological anomaly: a fully formed eye staring back from the inside of its mouth.
Decades later, that photograph remains the only evidence of this bizarre condition. The toad was never captured for study, leaving scientists with a tantalizing mystery. With no live specimen, every explanation for this "one-in-a-billion" creature remains a hypothesis. Here are the leading scientific theories, from the most likely to the purely speculative.
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Hypothesis 1 (The Most Likely): A Genetic "Macromutation"
The most probable and scientifically accepted explanation is a profound error in the toad's earliest embryonic development. This is known as a "macromutation," a large-scale mutation that dramatically alters the structure of an organism.
This theory centers on a group of master regulatory genes called homeobox genes, or Hox genes.
Think of Hox genes as the "master architects" of a developing embryo. During the early stages, they send signals that map out the entire body plan. They tell the embryo where to build the head, where to grow limbs, and, crucially, where to place the eyes. This process is incredibly precise.
In the case of the Gardner toad, it is hypothesized that a spontaneous "glitch" occurred in this genetic blueprint. The gene responsible for signaling "build an eye here" may have malfunctioned, causing the developmental instructions for an eye to be delivered to the wrong location the tissue destined to become the roof of the mouth instead of its proper place on the head.
This single genetic mistake would have been all it took to create this extraordinary anomaly.
Hypothesis 2: A Parasitic Sabotage
Another compelling, though less likely, theory involves a parasitic infection during the tadpole stage.
Scientists know that trematode flatworms are notorious for causing horrific deformities in amphibians. These parasites are known to infect tadpoles and physically disrupt their development, often leading to frogs with multiple extra legs or missing limbs.
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The hypothesis suggests that one of these parasites may have encysted (burrowed into) the tadpole's developing head tissue. This physical "blockage" or the chemical signals released by the parasite could have confused the embryo's developmental pathways, essentially "pushing" the developing eye tissue out of place and forcing it to form in the adjacent oral cavity.
However, without a specimen to examine for parasitic cysts, this remains speculation. Furthermore, while trematodes are known for causing limb deformities, an eye displacement of this specific nature has not been documented as their typical handiwork.
Hypothesis 3 (The Least Likely): Environmental Toxins
Naturally, suspicion also fell on environmental factors, such as chemical pollution. Could toxins in the water have caused this mutation?
This theory is generally dismissed by experts for two primary reasons:
Lack of Evidence: The area where the toad was discovered was not known at the time to be a hotbed of high industrial pollution that would cause such severe mutations.
Specificity: Chemical toxins often cause widespread, systemic issues (like cancers or stunted growth) rather than a single, complexly misplaced organ.
Without the ability to perform a necropsy or take tissue samples, it is impossible to know what chemicals, if any, the toad was exposed to.
An Enduring Mystery
Because Scott Gardner's photograph is the only data available, the toad with an eye in its mouth will likely remain a captivating biological mystery. We have no way of knowing if the eye was functional, if it had a proper nerve connection to the brain, or if the toad lived a normal life.
However, the consensus leans heavily toward the first hypothesis. This was not a creature from folklore, but a real-life example of a spontaneous macromutation a rare, random error in the genetic code that reminds us how complex, and occasionally fallible, the blueprint of life can be.