The dream of this research is the cure of diseases like Huntington’s. Those cures may come in time, but the lesson of period counsels patience. In this lesson there is also some consolation. If the dream is still some distance away, then so is the nightmare. The nightmare is the development of the kind of genetic engineering project that would diminish whole generations’ sense of free will. Everyone who works in the field hears questions like “Have you found the free-will gene yet?” It is a joke that contains the essence of the late-twentieth-century horror that Benzer’s science has opened. And the assumption behind the nightmare is that someone could engineer or reengineer that gene as easily as a genetic engineer can now change the clockwork gene and transform a fly’s sense of time.
However, the actual clockwork of the fly is turning out to be so complex—and more pieces of the clock are still to be discovered—that it looks less like an invitation to human intervention and more like a cautionary tale or object lesson for anyone who might try, in the twenty-first century, to improve on nature’s four-billion-year-old designs. Molecular biologists have now been mutating and examining thousands of generations of flies, and they have not made a better clock or a better fly yet.
In 1962, the year Benzer began to think about his study of genes and behavior, the novelist Anthony Burgess published A Clockwork Orange. Burgess later explained the title: “I mean it to stand for the application of a mechanistic morality to a living organism oozing with juice and sweetness.” Even then, when most scientists thought in terms of nurture rather than nature, Burgess was worried that a science of behavior and mechanistic morality might rob us of free will. A Clockwork Orange is the story of a young convict forcibly conditioned by the methods of behaviorists to abjure violence. The novel explores the nightmare of total control of behavior from outside, the way science fiction novels today explore the nightmare of total control from the inside. Burgess’s prison chaplain doubts that the reprogramming of the novel’s antihero will constitute a real improvement: “The question is whether such a technique can really make a man good. Goodness comes from within, 6655321. Goodness is something chosen. When a man cannot choose he ceases to be a man.”
And again: “What does God want? Does God want goodness or the choice of goodness? Is a man who chooses the bad perhaps in some way better than a man who has the good imposed upon him? Deep and hard questions, little 6655321.”
ONE OF THE BEAUTIES of the clock for molecular biologists has always been its neutrality. A clock is not a loaded subject—except as a symbol for all the rest of the living machinery that the fly clock is now teaching scientists to study, much the way the deconstruction of clocks and flies has taught generations of young boys to become scientists.
Of course, the other mutants that came out of Benzer’s Fly Room are not emotionally neutral; and in the 1990s, as these studies advanced too, gaining by monthly advances in the powers of molecular biology, the Benzer school’s work at last began to emerge into the light and heat of the world’s attention.
Jeff Hall and his technicians have a Fly Room they call Paradise, because they keep it at a constant Bahamian temperature. In Paradise, fruitless flies in rows of glass vials go round and round, chaining from dawn till dusk. Hall is now working with a whole consortium of other Fly Rooms on the genetic dissection of fruitless. The mutation is turning out to be embedded in a gene complex at least as intricate as the orrery of period and much more sensitive politically.
Hall had gotten an early hint of the complexity of the instincts involved here when he made his gynandromorphs in Benzer’s Fly Room. If a gynandromorph has a female body and a male head, the head says, “Court,” while the body says, “Be courted.” The gynandromorph with the female body extends a wing and sings to females but sings a sort of gibberish song—unless there are patches of maleness in the thorax.
Hall and his team have now generated a long line of fruitless mutants. In essence, what they have done is to create a library of artificial fruitless alleles. They have fed innumerable strains of fruitless EMS and bombarded fruitless with gamma rays, all to make more mutants. Each group of fruitless mutants lives together in a vial for a few days before they start to chain. A technician in Hall’s lab monitors how long they take to chain and how much they chain when they do. Some vials are more fruitless than others. Depending on the damage in the genes, just a few flies in a vial may make just a few circles now and then. They break up and then come back together; they take little breathing spaces. They extend their wings, but not fully, making scissoring motions, almost as if they cannot get their wings out far enough or up high enough. Other vials seem to go crazy: with one wing out and shaking, the mutants dance in circles all day long in what looks to human eyes like a frenzy, waving their wing tambourines.
In 1989, fruitless was mapped by a postdoc in Hall’s laboratory. The mutation lies on the fly’s third chromosome. The original mutation was made by zapping flies with X rays. Now Hall could tell exactly what those X rays had done to the chromosome. The X rays had damaged it in two loci that lie very close together. A piece of DNA had popped out and then gotten stitched back into its chromosome backward. The X rays had caused an inversion, and this inversion has been passed down in every fruitless fly. In effect, fruitless is two mutations close together, one at each end of the inversion. Some of fruitless’s behavior maps to the break point at one end of the inversion: the fruitless male’s failure to copulate and his habit of chaining with other males. Another piece of fruitless behavior maps to the other end: the male’s ability to stimulate courtship in other males.
In the 1980s and 1990s, the pursuit of fruitless led Hall and others into a deep study of the origins of the differences between the sexes. As with the study of period, the findings turned out to have great generality. Why does one fertilized egg grow into a male nervous system and another into a female nervous system? What are the molecular events that determine sex? It was Morgan’s Raider Alfred Sturtevant who discovered the first sexual determination mutant, a gene he called transformer. When a female fly inherits two copies of transformer, her chromosomes remain female, and she still grows big, like a female, but otherwise she looks and acts like a male, with a male’s black belly and a male’s gift of song. Mutations like transformer have since been discovered in every imaginable kind of organism, including human beings.
What period is to the sense of time, fruitless is to sex: another demonstration of Konopka’s Law. It is a point of entry that is helping to lead molecular biologists inside what is now one of the best-studied stories of gene interaction in nature. Molecular studies have uncovered a whole cascade of genes that decides the sex of the fly. The point of origin of the cascade is a gene called Sex-lethal (discovered by another Raider, Hermann Muller). If a fly inherits two X chromosomes, then Sex-lethal is turned on. Sex-lethal turns on transformer; transformer and transformer-2 turn on doublesex; doublesex turns on a cascade of genes that give a fly a vagina, her feminine perfumes, and all the other sexual equipment of a fit female fruit fly.
On the other hand, if a fly inherits only one X chromosome, the cascade flows on a different course to doublesex, and doublesex then switches on a different cascade of genes. This cascade gives a fly a penis, masculine perfumes, and the celebrated sex combs that decorate the entrance to Hall’s laboratory, the Drosophila Arms.
Now, fruitless turns out to be one of the key genetic switches in this long cascade. The gene is in the category of tremendous trifles. As the apostle James observes, there are tiny objects in this world that are able “to bridle the whole body.” “Behold, we put bits in the horses’ mouths, that they may obey us, and we turn about their whole body.” The gene fruitless is such a bit. Some of this gene’s products are expressed only in the central nervous system, and only in about 500 out of the 100,000 neurons in the central nervous system. Of those 500, most cluster in groups of 10 to 30 cells, and they map to the sections of the nervous system that are required for carrying out the dance steps of co
urtship.
Sex in our kind is determined by cascades of genes too. A gene on the short arm of the Y chromosome starts the building of the testes and makes a human embryo male. This gene was cloned in 1990 and named sry (for “sex-determining region, Y chromosome”). Mutations in sry can cause babies with two X chromosomes to develop as boys and babies with an X and a Y to develop as girls. The more molecular geneticists study these mutations, the better they will understand exactly what happens to make a man look at a woman or a woman look at a man and see the lineaments of gratified desire. These lineaments begin in lines of genetic code; they become elaborated in rich and complicated ways as the embryo grows, responding to the embryo’s inner and outer environments, Pascal’s two infinites.
In What Is Life? Schrödinger imagined that the physical structure of the gene would turn out to be the Lord’s masterpiece. But the gene itself is only the beginning. The true masterpiece is in the procession of interconnections of small wheels within bigger wheels within bigger wheels that make a life, a procession that merely begins with the lines of code in the gene. The more biologists study these wheels within wheels, the more complexity they find. Years ago the evolutionary biologist Julian Huxley warned of the danger of anthropomorphizing animals and the equal and opposite danger of mechanomorphizing them. We lose sight of the animal either way, he said: by imagining it is just like us or by imagining it is just like a machine. Now we can see the truth of this observation at the level of the clockwork mechanism itself, with period, and equally, with fruitless. At each turn, inside the growing embryo, a gene interacts with the genes around it, and in the adult animal each complex of genes interacts with many others and with the surrounding world in ways so complicated that we are only just beginning to explore them, even in a fly.
CHAPTER SIXTEEN
Pavlov’s Hat
If knowledge isn’t self-knowledge it isn’t doing much, mate.
—TOM STOPPARD,
Arcadia
WHEN CHIP QUINN left Benzer’s Fly Room, he took the memory project with him. In a Fly Room of his own at Princeton University, he went on poisoning flies and running their children through his Teaching Machine. In this way he found more slow learners to keep company with the original dunce, including amnesiac, smellblind, turnip, and rutabaga. But Quinn was groping. Memory was a black box, and he did not know how to get inside it. As one of Benzer’s student’s students observed afterward, dunce, turnip, and cabbage all showed “essentially the same overt phenotype: stupidity.” Quinn could not distinguish whatever was wrong with dunce from whatever was wrong with rutabaga.
One day a grad student of Quinn’s, Ronald Booker, fixed a fly to the end of a wooden stick with a dab of wax. He tied a slipknot in a fine wire to make a noose and looped the wire over one of the fly’s legs. He cinched it tight by pulling on it with a forceps and snipped the wire so that one end dangled loose. Then he suspended the little fly over a pool of salt water so that the wire just brushed the surface. The fly waved and kicked its leg, and the wire lifted out of the water and dipped back in. Whenever the wire touched the water, the fly got an electric shock. Normally, Quinn’s wild-type flies were uncertain learners, as Benzer’s nemesis Jerry Hirsch had pointed out. But hanging over the electrified pool, better than nine out of ten wild-type flies learned to keep that leg up.
Then Booker tried pinching off the fly’s head with a hot forceps or cutting it off with a razor blade while the fly hung over the water. Not only did the fly survive decapitation, it learned to keep the wire out of the water even better than a fly with a head. Flies have nerves outside the brain, just as human beings do, and apparently those nerves were learning the lesson. Quinn and Booker could only assume that the flies learned better without their heads because they were less distracted.
However, dunce, turnip, and rutabaga flunked this leg-lifting test with or without their heads, just as they flunked all of Quinn’s other learning tests. Something was different in both their genes and their nervous systems. But to find out exactly what, Quinn wrote in 1981, “we will need more sophisticated tools than hot forceps and a razor blade.”
That year, Quinn took on a new postdoc, Tim Tully, who was probably as passionate about the study of memory as Quinn had ever been. When Tully was a boy, a day of childhood memories had been knocked out of him in a Christmas accident. Hitting a tree with his sled had produced a kind of hollow of amnesia; he had lost all memory of the hours preceding the accident. (A quick dunk in ice water will do the same thing to a fruit fly.) When he was in college, studying with Jerry Hirsch, Tully decided that finding the secret of memory was the only thing he wanted to do in his working life. And after studying the literature he decided that Benzer’s method of genetic dissection was a more promising tool than Hirsch’s method of breeding and crossbreeding flies. He told Hirsch that Benzer was discovering molecules; Hirsch was not. Tully often says that Hirsch regarded him as a reincarnation of Judas for going over to Benzer. “And in a way perhaps I was,” Tully says. “Although I never kissed him on the cheek.”
Tully joined Quinn at Princeton and took stock of Quinn’s operation. He was just as blunt with Quinn as he had been with Hirsch. In his view, Quinn’s problem was the inefficiency of his screen. Quinn’s headless fly had proven that flies are capable of much better performances than they ever achieved in Quinn’s Teaching Machine.
Tully has a knack for gizmos and gadgets. He designed a new Teaching Machine. He piped in the odors silently and smoothly on soft breezes so that all the flies would get the same doses of his perfumes. He lined the shock tubes in such a way that every fly would feel every jolt. He designed each part of the machine to run quietly and efficiently so that the flies would not be distracted from their lessons and so that virtually every one would get virtually the same lesson every time. He used a little plastic elevator to lift the flies gently from one stage of the experiment to the next. Designing and building this machine took Tully four years.
Human eyes can see dim red light, but fly eyes cannot. So when Tully was ready to run his new Teaching Machine, he turned out the lights and watched the flies by the glow of a low-watt darkroom safelight. In the dark and quiet of the new machine, fruit flies acted much calmer than they ever had in Quinn’s, and Tully was delighted to find that better than nine out of ten of them now learned their lessons. Tully had gotten rid of the static—which is what Quinn and Booker had done much more crudely with the hot forceps and the razor blade.
Now, because the flies in the new Teaching Machine were not distracted from their lessons, Tully’s experiments were not blurred by the random noise of good learners that failed to learn. And now Tully could discern varieties of stupidity, a wide spectrum of troubles in Quinn’s mutants. He discovered that rutabaga, for instance, is able to learn; it just forgets fast. In other words, rutabaga is a memory mutant but not a learning mutant. Other mutants have trouble learning, but they hold on to what they do learn. They are learning mutants but not memory mutants.
During those long early years of R and D, Tully had the same public relations problems that had always plagued Benzer’s school. Most biologists found it hard to take a fly in a Teaching Machine seriously, and Tully had trouble getting any funding for his project. When James Watson first got interested in Tully’s work, Watson’s advisers urged him to stay away. But Watson installed Tully in the laboratory next to his office at Cold Spring Harbor, and slowly Tully began dissecting the act of memory in his flies.
For years, Tully had been reading the papers of the neurobiologist Eric Kandel, who is now at Columbia University. Kandel was working on learning and memory in a giant snail, Aplysia. When Kandel tickled the siphon of the snail, it flinched and contracted its gill. But when Kandel tickled the snail ten or fifteen times, it flinched less and less. The snail was learning to ignore him. If he smacked the poor snail on the head, it suddenly became much more responsive again.
Kandel and his colleagues managed to trace the circuit of neurons that gover
ns these simple reflexes. The team stuck a microelectrode into a single neuron and recorded the characteristic pattern of bursts of electricity, like a series of dots and dashes in Morse code, that made the gill flinch. In one experiment, Kandel sent precisely that same series of spikes into a motor neuron. The gill flinched. Kandel was learning the snail nerve’s language, the way King Solomon in the legend learned the languages of the beasts, fowl, and fishes.
From there Kandel played with some of the molecules that compose the message; this was the work that fascinated Tully. One nerve sends another nerve a message across the synapse between them. The message takes the form of a packet of molecules—or a burst of packets. When the snail gets knocked on the head, a message shoots down a nerve from its head and activates an enzyme called adenylate cyclase in the gill nerve. This enzyme helps the gill nerve make a second compound called cyclic adenosine monophosphate, or cAMP. The cAMP then cranks up the nerve cell’s sensitivity so that the next time the siphon is tickled, that cell will release more packets across the synapse. In this way, the memory of the blow to the head has left a trace in the snail: the snail will flinch harder the next time it is tickled in the siphon because it has just been struck. It is a simple case of learning and memory, reduced to a few molecules.
At Caltech, Benzer and his student Duncan Byers were following Kandel’s work too. Since cAMP matters so much in the learning and memory of the snail, they decided to take a second look at their fly mutant dunce. They were thrilled to discover that dunce makes a crippled form of the enzyme cAMP phosphodiesterase. Without that enzyme, dunce has problems metabolizing cAMP. So at this level, at least, the language of the fly and the snail seemed to be the same. Benzer and his students wondered if the enzyme cAMP might be part of a universal mechanism of learning and memory in the living world.
Time, Love , Memory Page 23