I used to show students a film made by the French zoologist Faure‑Fremiet on the feeding behavior of protozoa. Many of our sturdiest concepts of the apparatus required for animal behavior are mocked by these animalcules, particularly by the ciliates; for in one cell they do everything: move about, react to stimuli, feed, digest, excrete, on occasion copulate and reproduce. In this film one saw them encountering problems and solving them, much as would a mammal. I remember best a carnivorous protozoon tackling a microscopic bit of muscle. It took hold of the end of a fibril, and backed off at an angle, as though to tear it loose. When the fibril would not give, the protozoon came in again, then backed away at a new angle, worrying the fibril loose, much as a dog might have done, worrying loose a chunk of meat. It was hard, watching that single cell at work, not to anthropomorphize. Did it know what it was doing?
But then, ciliate protozoa are the most complex cells we know. How about a cell highly specialized to perform a single function in a higher organism, a nerve cell for example, that can only transmit an impulse? Once, years ago, I was visiting the invertebrate physiologist, Ladd Prosser, at the University of Illinois in Urbana. He took me into his laboratory, where he was recording the electrical responses from a single nerve cell in the ventral nerve cord (which takes the place of our spinal cord) of a cockroach. It was set up to display the electrical potentials on an oscilloscope screen, and simultaneously to let them sound through a loudspeaker. I was hearing a slow, rhythmic reverberation, coming to a peak, then falling off to silence, then starting again, each cycle a few seconds, like a breathing rhythm. Prosser remarked, “That kind of response is typical of a dying nerve cell.”
“My God!” I said, “It’s groaning! You’ve given it a voice, and it’s groaning!”
Was that nerve cell expressing a conscious distress? Is something like that the source of a person’s groaning? There is no way whatever of knowing.
So that is the problem of mind -- consciousness -- a vast, unchartable domain that includes all science, yet that science cannot deal with, has no way of approaching; not even to identify its presence or absence; that offers nothing to measure, and nothing to locate, since it has no location.