The glass frog’s transparent bellies and light-green skin blend in against leaves in the underbrush. A close relative to the glass frog is the red-eyed tree frog, which derives its name from a distinctive red-eye and neon skin color. They are nearly the same size, with similar physical structure, yet natural selection caused visual changes from their common ancestors. While glass frogs adapted by perfecting camouflage against leaves, these tree frogs have developed skin colors so bright they confuse predators, giving the frogs time to escape.
Both of these families may have the European common brown frog as a common ancestor, unremarkable with its medium size and yellow-brown coloration. While this frog usually camouflaged well within marshes or in mud, it would not be able to survive in the Amazons. After all, this new environment was heavily dependent on visual vibrance for survival. Through many generations, frog offspring with visual advantages had a better chance of surviving and passing their genes onto the next generation. These advantages would become more common as it became the norm, and the previous traits would become fossil (outdated) genes. For the European brown frog, genes responsible for brown pigment and large size may have become fossil genes with enough generations.
There is evidence that selective pressure caused red-eye tree frogs to copy poison dart frogs, as the vibrant color may have persuaded predators that they were very poisonous. Through a process known as descent with modification, mutations or behavior that resulted in colorful skin survived and built up until each member of the species had colorful skin.
As for the glass frog, a trait that almost guaranteed survival was versatile camouflage, and it may have also gotten greener and more transparent through each passing generation due to higher survivability. All in all, While glass frogs and red-eye tree frogs are not the same species (after all, they are found in different locations and do not have the ability to interbreed), it is possible that they may have descended from organisms such as the European common brown frog.
The underbelly of the glass frog is so transparent that viewers can observe its heartbeat:
0:15 – 0:27 https://www.youtube.com/watch?v=FAq1kSwm1Do