A Quick Reminder in Seconds
In Part One of this three-part series, we encountered the remarkable story of a toad photographed by a Canadian photojournalist in 1992. The animal was so unusual that many people initially suspected the photograph was a hoax or practical joke. The toad appeared to have no visible eye sockets; instead, both eyes seemed to be embedded in the roof of its mouth. The extraordinary image soon spread across Canada and the United States and later appeared in scientific publications and popular science books.
In Part Two we explored the developmental biology behind this astonishing abnormality and examined how major disruptions during embryonic development—sometimes described as macromutations [1]—might produce such an extraordinary anatomical outcome.
But can a toad with its eyes inside its mouth live a normal life? How does it manage to eat, hunt, and escape from predators? And why are scientists so fascinated by such extraordinarily rare cases? We’ll explore these questions in Part Three as we continue this remarkable story and discover what this unusual developmental anomaly can teach us about the hidden processes of growth and evolution in the natural world.
Now, in this third and final part, we return to the question that perhaps matters most: Could a toad with its eyes inside its mouth actually survive and live a relatively normal life? We will also explore why cases this rare and unusual continue to fascinate scientists—and what they can teach us about the remarkable flexibility, complexity, and sometimes unpredictability of animal development.
Surprisingly, the answer is yes.
Although a toad with eyes inside its mouth undoubtedly has impaired vision, the eyes themselves may remain functional. By opening its mouth, the animal can still detect light and movement.
Even more remarkable is the way frogs and toads normally use their eyes during feeding. When swallowing relatively large prey such as insects, many species retract their eyes downward into the roof of the mouth. This movement helps push food toward the throat, making swallowing more efficient. In a sense, the eyes of a healthy frog already move partway into the mouth during feeding, making the abnormal position somewhat less disruptive than it might first appear.
Why Are Macromutations Important?
The famous “mouth-eyed” toad is only one example of the extraordinary developmental abnormalities scientists have documented in amphibians. Both in nature and in laboratory studies, researchers have observed duplicated limbs, missing limbs, extra eyes, two-headed embryos, malformed jaws, misplaced organs, and numerous other developmental anomalies. Similar abnormalities have also been recorded in fish, reptiles, birds, mammals, and even insects such as the fruit fly, whose mutations helped scientists discover many of the genes responsible for organizing the body during embryonic development.
Far from being mere curiosities, these unusual animals have become invaluable scientific tools. By studying developmental mistakes, researchers have gained a deeper understanding of how healthy organs normally form, why birth defects occur, how cells communicate during embryonic development, and how developmental genes coordinate the construction of an entire organism. This knowledge has transformed modern biology and now contributes to fields as diverse as developmental genetics [2], regenerative medicine [3], stem-cell research [4], tissue engineering [5], evolutionary developmental biology (“evo-devo”) [6], and the study of congenital disorders [7].
The extraordinary toad photographed more than thirty years ago is therefore much more than a biological oddity. It serves as a powerful reminder that constructing a living organism is one of nature’s greatest engineering achievements. From a single fertilized egg, billions of cells must divide, migrate, communicate, and exchange molecular instructions that determine when, where, and how every organ will develop.
Almost every time, this astonishing process unfolds with extraordinary precision.
Occasionally, however, a tiny error in those developmental instructions gives rise to an animal so remarkable that it not only captures our imagination, but also deepens our understanding of one of biology’s greatest mysteries: how life builds itself.
Notes
1. Macromutations
Macromutations are large-scale genetic changes that can produce major alterations in an organism’s body structure or development. Unlike small mutations that may affect a single characteristic, macromutations can sometimes affect entire body parts or developmental patterns.
2. Developmental Genetics
Developmental genetics is the study of how genes control the growth and development of an organism from a single fertilized cell into a complex individual. It examines how genes regulate processes such as cell division, differentiation, tissue formation, and the development of organs.
3. Regenerative Medicine
Regenerative medicine is a field of medicine that aims to repair, replace, or regenerate damaged or diseased cells, tissues, or organs. It uses approaches such as stem cells, tissue engineering, and biological molecules to restore normal structure and function.
4. Stem-Cell Research
Stem-cell research investigates cells that have the ability to reproduce themselves and, under appropriate conditions, develop into different specialized cell types. Researchers study these cells to understand development and disease and to explore potential treatments for damaged tissues and organs.
5. Tissue Engineering
Tissue engineering combines cells, biomaterials, and biological signals to create or restore functional tissues. Its goal is to develop biological replacements for damaged tissues—for example, engineered skin, cartilage, bone, or other tissues—that can integrate with the body.
6. Evolutionary Developmental Biology (Evo-Devo)
Evolutionary developmental biology is a field of biology that studies the relationship between evolution and embryonic development, including how changes in genes and developmental processes can contribute to biological diversity across generations. It helps scientists understand how small or large changes in developmental programs can produce differences in body form and structure and, potentially, give rise to new traits during evolution.
7. The Study of Congenital Disorders
The study of congenital disorders focuses on conditions or abnormalities that are present at birth and may result from genetic factors, disturbances during embryonic development, or a combination of factors. Understanding these disorders helps scientists and physicians learn how organs develop, why abnormalities may occur during their formation, and how some of these conditions can be prevented, diagnosed, or treated.
References
1. The Travel Staff. “A photographer in Canada found a toad with eyes in its mouth, and scientists were baffled.” The Travel, June, 24, 2026.
https://www.thetravel.com/photo-of-toad-with-eyes-in-mouth-found-in-canada
2. Developmental Biology. (2020). Developmental Biology (12th ed.). Sinauer Associates / Oxford University Press.
3. Principles of Development. (2019). Principles of Development (6th ed.). Oxford University Press.
4. John Gerhart, J., & Marc Kirschner, M. (1997). Cells, Embryos, and Evolution. Blackwell Science.
5.. Langman’s Medical Embryology. (2024). Langman’s Medical Embryology (15th ed.). Wolters Kluwer.