Shufflebrain

I set up an entire series of guppy-to-salamander cerebral transplants to answer a number of subsidiary questions about what I was now calling "temperature-dependent feeding behavior." How often would it occur? About 70 percent of the time. What was the critical temperature? I determined that it was 17-18 degrees centigrade--for the donors as well as the hosts. When, postoperatively, did temperature-dependent feeding emerge? In a little more than two weeks. (Thus, it wasn't like injecting tissue extracts, but more like the wait for a graft to take.) Checking Buster's records, I realized that had the fire drill taken place perhaps a day or two earlier, I never would have made the observation.

Then one day, six weeks after his operation, after having fasted twenty-four hours in the cold, Buster hauled off and ate a worm. For a moment I was sick enough to cry. Had it all been just a fluke? But that same day, the transplanted guppy hearts beat their last beats. Rejection! And five to six weeks after the new batch of guppy-to-salamander hosts had been operated on, they too reverted to feeding at low temperature. I was sorry to see the trait disappear. But its disappearance made the story as complete as it could possibly have been.

Buster exemplified the independence principle. Punky the Tadamander gave us no basis to judge it. Buster's feeding behavior was a composite of salamander and guppy traits. Punky merely used his salamander body to display his tadpole mind. Buster's failure to attack worms at low temperatures did not mean that he lacked the necessary memories. The stimulus, a cool environment, had blocked his use of those memories. His reaction in the cool was negative, but an "active" negative (like a minus sign in the check book). Punky's refusal to attack worms during those 68 days stemmed from different causes entirely: his negative response was passive. As a control for my experiment with Punky, I performed operations in which I left most of the host salamanders' brains in place and substituted only the cerebrums with those of tadpoles. These animals, like Punky, always attacked worms. Thus, I had to conclude that in preparing Punky for his transplant--in amputating his original salamander midbrain, diencephalon, and cerebrum--I had removed his carnivorous memory, which his new tadpole brain did not restore to him. Placing the active-versus-passive comparison in the context of our earlier analogy with the deck of hologramic cards, Buster's failure to attack was similar to dealing out an inappropriate hand. When Buster's environment was warmed, we found that attack was in his deck after all. But no possible deal could have turned Punky into a killer; attack was not among his tadamander cards.

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Are Buster and Punky too remote from us to suggest anything about the human condition? During embryonic life, we develop through stages in which we look and act like fish, salamanders and tadpoles. Embryonic development provides convincing evidence for the theory of evolution. One principle of embryology, von Baer's law, holds that ontogeny recapitulates phylogeny, meaning that as we develop, we go through our own individual mini-evolutions, revealing our close kinship to other vertebrate creatures. Behavior doesn't start up when we slide out of the birth canal onto the obstetrics table. We're live cargoes in Mom's womb. And we're behaving long before we're born.

An old-time Georgia country obstetrician, Richard Torpin, used to show up every year at the meetings of the American Association of Anatomists with all sorts of novel and ingenious exhibits of human behavior in utero. From stillbirths and detailed records on his patients, Doc Torpin would reconstruct what led to a particular fetus's undoing. Using rubber bands and plaster of Paris, he produced models to illustrate various prenatal problems. One year he demonstrated how a restless fetus could get its fingers and toes tangled and, cut off from a blood supply at a period of intense growth, eventually lost in loops of umbilical cord. (He had found bits of detached fingers in the inner wall of the placenta.) In another exhibit, he showed how a swimming fetus had found and swallowed its own umbilical cord, much as a salamander or a guppy would down a worm. At birth, as the child tried to shift breathing air, it strangled on its own umbilical cord, Doc Turpin explained.