Belling the Mice

Are psychological traits inherited? Dr. Calvin S. Hall, of Western Reserve University, believes that some are. In the current Journal of Heredity, he reports experiments to prove his point. His subjects: mice. The trait chosen for study: "audiogenic seizures," i.e., dying in convulsions when scared by a sudden noise.

Dr. Hall selected two strains of adolescent (35 days old) male mice. One strain was black, the other "dilute brown." Both had been inbred by brother-&-sister matings for many generations, thus making sure that the strains would differ widely in hereditary characteristics, while individual mice within each strain would be almost alike genetically.

The apparatus was simple: a galvanized iron washtub with a strong light above it, and a loud electric bell hung inside its rim. Dr. Hall put his mice in the tub in small groups, and watched them for two minutes. The brown mice were slightly more nervous than the black, but also bolder: they ventured more frequently into the middle of the tub.

Then Dr. Hall rang the bell. At the terrifying sound, the black mice tended to crouch and "freeze." The brown mice scurried around the tub, 93% of them falling in convulsions. Nearly all of the ones with convulsions died. Nearly all the strong-nerved black mice survived the bell.

Next Step. Smiling happily at the success of this experiment, Dr. Hall proceeded to the next. Some of his brown mice, still untested, had unusual ancestry. They were descended from fertilized ova transplanted from a female brown mouse into the womb of a black one. All the "genes" in their cells were of brown-mouse origin. Only the nourishment materials which formed their infant bodies came from their foster mother.

Dr. Hall put these prenatal stepchildren into his tub and gave them the bell treatment. All had convulsions; two-thirds died. None behaved like noise-resistant black mice. This indicated, said Dr. Hall, that the tendency to die of audiogenic seizures is hereditary, carried by a gene in the germ plasm.

Final problem: Was this gene a "dominant" or a "recessive?" To find out, Dr. Hall mated brown mice with black mice. When their hybrid offspring were tried in the tub, nearly all died in convulsions at the sound of the fatal bell. This proved (according to Mendel's law of heredity) that the jittery gene was dominant. A recessive gene would not have expressed itself until the next generation.

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