Shufflebrain

Gelber prepared a pâté of her animal's favorite bacteria (a single paramecium may devour as many as 5 million bacilli in a single day[4] ); then she smeared some of it on the end of a sterile platinum wire. She dipped the wire into a paramecium culture. Immediately her animals swarmed around the wire, which was not exactly startling news. In a few seconds, she withdrew the wire, counted off a few more seconds and dipped it in again. Same results!. But on the second trial, Gelber presented the animals with a bare, sterilized wire, instead of with bacteria. No response! Not at first, anyway. But after thirty trials--two offers of bacteria, one of sterile wire--Gelber's paramecia were swarming around the platinum tip, whether it proffered bacterial pâté or not.[5]

Naturally, Gelber had her critics, those who dismiss the idea that a single cell can behave at all, let alone remember anything. I must admit, a mind isn't easy to fathom in life on such a reduced scale. Yet I've sat entranced at my stereoscopic microscope for hours on end watching protozoa of all sorts swim around in the water with my salamanders. I've often wondered if Gelber's critics had ever set aside their dogmas and doctrines long enough to observe for themselves the truly remarkable capabilities of one-celled animals. Let me recount something I witnessed one Saturday afternoon many years ago.

On occasion, a fungal growth infects a salamander larva's gills. To save the salamander, I remove the growth mechanically. On the Saturday in question, I discovered one such fungal jungle teeming with an assortment of protozoa. What were those beasts? I wondered. Instead of depositing the teased-off mass on the sleeve of my lab coat, I transferred it to a glass slide for inspection under the much greater magnification of the compound phase microscope.[6]

Several different species of protozoa were working the vine-like hyphae of the fungus. I was soon captivated by the behavior of a species I couldn't identify. They were moving up and down the hyphae at a brisk pace. At the distal end of a strand an animal's momentum would carry it out into the surrounding fluid. It would then turn and swim back to its "own" hypha, even when another one was closer. Something spatial or chemical, or both, must be attracting these critters, I thought almost out loud. Just as I was thinking the thought, one animal attracted my attention. It had just taken a wide elliptical course into the fluid; but along the return arc of the excursion, another hypha lay directly on its path. And my little hero landed on it. After a few pokes at the foreign strand, the animal paused as though something didn't seem quite right. Meanwhile its sibs were busily working the territory. After a few tentative pokes, my animal moved away. But now it landed on a third hypha, shoved off after a brief inspection and landed on still another hypha. Soon it was hopelessly lost on the far side of the microscopic jungle.

But then something happened. As I was anticipating its departure, protozoan hesitated, gave the current hypha a few sniffs and began slowly working up and down the shaft. After maybe five or six trips back and forth along the strand, my animal increased its speed. Within a few minutes, it was working the new hyphas as it had been when it first attracted my attention. I couldn't escape the thought that the little creature had forgotten its old home and had learned the cues peculiar its new one.

Had I conducted carefully controlled experiments, I might have discovered a purely instinctive basis for all I saw that Saturday. Maybe Gelber's or Day and Bentley's observation can be explained by something other than learning, per se. But, instinctive or learned, the behavior of protozoa--or bacteria--doesn't fit into the same class of phenomena as the action-reaction of a rubber band. Organized information exists in the interval between what they sense and how they respond. We employ identical criteria in linking behavior to a human mind.

***

But higher organisms require a "real" brain in order to learn, don't they? If posing such a question seems ridiculous, consider an observation of a physiologist named G. A. Horridge made some years ago on decapitated roaches and locusts.

In some invertebrates, including insects, collections of neurons--ganglia--provide the body with direct innervation, as do the spinal cord and brainstem among vertebrates. Horridge wondered if ganglion cells could learn without the benefit of the insect's brain. To test the question, he devised an experiment that has since become famous enough to bear his name: "The Horridge preparation."