When the Frog's Hand Cleans the Frog's Stomach


When the Frog's Hand Cleans the Frog's Stomach

A personal take on science

by Delilah Foss, AIR staff


Which hand does the frog use to clean its stomach?

This seemingly mundane question leaps up when you read David Sims, Paul Andrews, and J.Z. Young's new report, "Stomach Rinsing in Rays" (Nature, vol. 404, April 6, 2000, p. 566). Sims, Andrews, and Young explore the method by which certain fish "remove noxious material from the stomach." Called "full gastric eversion," this consists of turning the stomach inside out and draping it through the mouth.

The key sentence in Sims, Andres, and Young's paper is:"In frogs and toads, stomach eversion is accompanied by 'gastric grooming' with the right hand to wipe away vomitus."

The authors are specific about it being the RIGHT hand. No mention is made of a frog using its left hand.

I Question Whether Left Can Be Right

But can they be certain about this? Is it always the right hand?

There is, after all, research indicating that frogs, like many other animals, can be right- or left-handed. (See, for example, M.J. Morgan's "The Asymmetrical Genetic Determination of Laterality: Flatfish, Frogs and Human Handedness," Ciba Foundation Symposium, vol. 162, 1991,pp. 234-47.)

Do ALL frogs use their right hand to clean their stomachs? And if so, does this right-handedness have a biological cause, or could it be something cultural? Amongst humans, for example, some groups insist on using always the left hand for the "unclean act" of wiping themselves, and reserve the the right hand for "clean" acts such as eating.

The question is there. It must be answered. What does the frog's brain tell the frog's hand -- and which hand does it tell it to? I shall not rest until I find out.

(Thanks to Kevin B. Marvel and Jay Pasachoff for bringing the ray stomach rinsing paper to our attention.)

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