Look before you leap

There is something bucolic about frogs. Our almost universal fascination with them and their thoroughly endearing characteristics is probably responsible. Don’t be fooled though by their beguiling nature, because frogs have valuable lessons to teach us about ocular evolution, visual processing, and binocularity.

Members of the class Amphibia, from the Greek meaning “double life,” represent intermediate steps from an aquatic life to a terrestrial one that probably occurred during the late Devonian period, approximately 375 million years ago. Somewhere between Ichthyostega, a long extinct, tetrapod predator, and the coelacanth, a lobe finned fish, vertebrates first came ashore. These early amphibians breathed air, but were dependent for their reproduction upon water. All three extant orders of the class Amphibia—Anura (frogs), Urodela (salamanders), and Caecilia (a group of blind worm-like animals)—retain that echo of evolution, since all require water for their eggs and early developmental stages.

Both frogs and salamanders retain accommodative mechanisms resembling those of cartilaginous fishes, but many frog species seem to have lost …