Weekend Special

I Can't Believe What I'm Seeing: A Springtime (Froggy) Miracle

Robert Krulwich stares at a frozen frog.
NOVA scienceNOW

Two weeks ago this animal was frozen solid. If you found one in the woods, packed in the topsoil, hiding under a leaf, you could pull it from the ground and it would feel like an ashtray. You could bang it (lightly) on a table — it would go, "Konk!" like a rock. It doesn't seem to be breathing. It reacts to nothing. It's so dead. Or seems to be. And then, this (I want to call it a miracle) happens ...

I did this piece when I was host of Nova Science Now, on PBS, and the mystery of it still amazes me. In particular, I can't stop wondering how the return of warm sunshine in springtime, which acts on the surface of the animal, triggers a sequence deep inside. There must be a cavalry of chemicals — little Paul Reveres that live near the animal's skin — that are roused by the warmth, then race into the body crying, "The sunshine is coming! The sunshine is coming!"

How else to explain the riddle of the wood frog's awakening? If its heart turns on before its brain, the brain would be too cold to get oxygen; the circulatory system would dam up and fail. If the brain turns on before the heart, that brain would be starved for oxygen and die. Yet somehow, all the organs in this little guy's body awaken in perfect synchrony — brain, heart, nervous system (even its inner Romeo) — and stretching its little legs, it announces, like an itty-bitty Schwarzenegger (so the ladies can hear) ..."I'm back!"

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