In 1971, researchers moved five adult pairs of Italian wall lizards (Podarcis sicula) from the islet of Pod Kopište to the neighboring island of Pod Mrčaru in the Adriatic Sea. Left untouched for decades, the transplanted population underwent an astonishing transformation. When evolutionary biologists returned to Pod Mrčaru in 2004, they discovered that the introduced lizards had multiplied into thousands and undergone rapid phenotypic evolution in under 36 years.
Facing a different ecosystem with abundant plant material rather than the insect-rich diet of their origin island, the Pod Mrčaru lizards shifted from a predominantly insectivorous diet to a herbivorous one. To process tough plant cellulose, the lizards evolved entirely new anatomical features, most notably cecal valves—muscular folds in the gut that slow down food passage and create fermentation chambers for symbiotic microbes. Cecal valves are extremely rare in lacertid lizards, making their emergence in just a few decades a landmark example of rapid microevolution.
Along with gut changes, the lizards developed larger heads with stronger bite forces to grind leaves, alongside altered social behaviors, proving that macro-level physical adaptations can emerge far faster than previously believed.