What is it men in women do require?
The lineaments of Gratified Desire.
What is it women do in men require?
The lineaments of Gratified Desire.
—WILLIAM BLAKE,
“The Question Answer’d”
DARWIN DIVIDED the adaptations of life into two kinds: the ones we need to survive and the ones we need to reproduce. The clock is one of the oldest adaptations of the first kind. Living things needed clocks as soon as they had begun to accumulate other adaptations: they needed clocks to organize the rest. Having a clock allowed the first simple life-forms billions of years ago to grow on a schedule—to make any compounds they required for photosynthesis before sunup, for instance, and to taper off their production before sundown, as plants still do today; or to hunt for other living things to eat when those things were most plentiful and most vulnerable—which owls and wolves still do today, each to its own clock. Inventing a clock was probably one of the first acts of life, and that is why clocks are ubiquitous. With period, Benzer and Konopka were looking at the first known specimen of one of the oldest instincts on the planet.
What is going on in our heads when we feel the passage of time is a question that they were wise enough to ignore, temporarily. That problem has defeated philosophers for millennia. Bishop Berkeley tried to define time and found himself “embrangled in inextricable difficulties.” Saint Augustine said that we all know what time is until we try to put it into words. The Roman philosopher Plotinus thought the sources of time must lie inside us, that time springs from the human soul.
A clock gene is not the same as the sensation of time, any more than a cascade of molecules in the retina is the same as the sensation of sight. Still, without rhodopsin and a long string of other molecules we are color-blind, and without clock genes we are time-blind. So period is a way into one of the sources and wellsprings that Plotinus believed must flow from the soul in “all the dense fullness of its possessions.”
There was something thrilling but also peremptory, down to earth, even absurd about the discovery of the first clock gene, as there would be about all the rest of the discoveries that followed. To go from the contemplation of time to the contemplation of clock genes means coming down to earth with a bump. To turn from the sublime to a mechanism so anatomically concrete can make us feel ridiculous. In his celebrated M notebook (M for Metaphysics, Materialism, and Mind) Darwin jotted a note to himself about Plato. “Plato says that our ideas arise from the preexistence of the soul, and are not derivable from experience,” Darwin wrote, and he added “—read monkeys for preexistence.”
But there are wheels within wheels even in period. Eventually molecular biologists in laboratories around the world would be bent over Konopka’s clock gene like scholars bent over a single verse of Hebrew or Greek in which they could almost read the secret of life. “Parmenides,” writes David Park in his book The Image of Eternity: Roots of Time in the Physical World, “was known principally for a poem, written in high poetic style, in which he analyzed the mysteries inherent in the single Greek word esti, ‘is.’ ”
TO TURN FROM the springs of time to the springs of love means coming down even harder. Love is what wise men and proverbs do not pretend to explain. “Three things are too wonderful for me,” a verse declares in Hebrew Scripture, “four I do not understand”:
the way of an eagle in the sky,
the way of a serpent on a rock,
the way of a ship on the high seas,
and the way of a man with a maiden.
In The Gold Bug Variations, a novel about the cracking of the genetic code, Richard Powers imagines a meeting between Albert Einstein and T. H. Morgan at Caltech. Morgan explains what he is trying to do in his Fly Room, the union he is trying to arrange between biology, chemistry, and physics. “No, this trick won’t work,” Einstein cries. “How on earth are you ever going to explain in terms of chemistry and physics so important a biological phenomenon as first love?”
In Darwin’s terms, the adaptations of reproduction are as old as the adaptations of survival. Reproduction is one of the defining acts of life; and without reproduction there would be no way for the Darwinian process to begin, since Darwin’s process is evolution by the selective success and failure of populations of reproducing forms. Small differences written in single changes in the letters of the double helix led rapidly under the pressure of natural selection to an extraordinary profusion of forms and also to forms of self-advertising, courtship, and copulation that are as miraculous as any phenomena in the natural world.
If the clockwork gene stands for all the clockwork of the body’s apparatus of survival, then the instincts of reproduction stand in our minds for all the miraculous complexity of behavior. Males and females need displays to find each other, to recognize each other, and also to impress each other, since virtually every copulation in the world takes place beside a big gene pool of competition. This produces powerful evolutionary pressures that Darwin called sexual as opposed to natural selection.
Galton assumed that other animals cannot vary their courtship routines the way we humans do with fashions. But humpback whales sing songs that radiate through the oceans for thousands of miles and change from season to season much like the Top Ten songs that fill the airwaves over the whales’ heads. At any one moment in any one ocean all of the males sing the same song. But within a month they will all be singing a new song, and unlike human beings they never sing a golden oldie from a decade or two back. They never repeat themselves. The songs appear to be courtship songs, elaborate displays, like most of ours on the radio. They actually include the use of rhyme; and according to Roger Payne, who has been recording them since the 1960s, the love songs of some whales are audible more than ten thousand miles away. “When you swim up next to a singing whale through the cool blue water,” Payne writes, “the song is so loud, so thundering in your chest and head, you feel as if someone is pressing you to a wall with their open palms, shaking you till your teeth rattle.”
Male bowerbirds in Australia and New Guinea do not sing fancy songs or flash fancy plumage. Instead they build bowers, pretty little shelters, each species according to its own design. Some build teepee style, with branches leaning in against a sapling that bowerbird watchers call a “maypole.” Others build what are known as avenue bowers, which they invite females to walk through. The satin bowerbird paints the walls with a twig brush; he makes the paint out of chewed fruit, charcoal, and his own saliva. Other bowerbirds drag in live orchids. They throw out the old, wilted flowers every day and redecorate the bower with fresh flowers. Males trash each others’ bowers, steal each others’ flowers, and even barge in sometimes to interrupt other pairs in coitus. The satin bowerbird, which has bright blue eyes, decorates its painted bower with anything blue it can find, according to the ornithologist Frank Gill: “One bower was decorated with parrot feathers, flowers, glass fragments, patterned crockery, rags, rubber, paper, bus tickets, candy wrappers, fragments of a blue piano castor [sic], a child’s blue mug, a toothbrush, hair ribbons, a blue-bordered handkerchief, and blue bags from domestic laundries.”
These spectacular animals would have been impractical subjects for attempts to isolate links between genes and behavior. Again the molecular biologists had to start simpler. Sydney Brenner studied mutants of courtship and copulation in the nematode worm. The worm is slow and undulant. Watching it through a microscope at high power is like watching whale sinuosities through a porthole. It glides around a petri dish on a bed of agar and around its food, a blob of E. coli in the center of the agar. Generations in Brenner’s school have now gotten to know the slither look of them, the male nosing around the female—wrapping around her, searching efficiently for the vulva, and finding it with the ingenuous directness or excitement of the young Philip Roth. Brenner and his students learned the worm’s ways and habits, which are highly regular (“Let’s give it forty-five seconds, and it will defecate again.”), and they learned to pick them up with toothpicks or titanium wire and to freeze and unfreeze mutants for their genetic dissection experiments. Like the drosophilists, they fell in love with their animals and saw more and more richness of behavior. There is a worm lab just down the hall from Benzer’s Fly Room at Caltech. It is run by a young molecular biologist named Paul Sternberg, who keeps three or four thousand strains of mutants, double mutants, and triple mutants frozen in liquid nitrogen for breeding experiments. Often when he and his group make mutants and something goes wrong, he becomes aware for the first time of some piece of normal behavior that he hadn’t noticed before. “If you’re narrow-minded like we are,” says Sternberg, “you don’t realize it until you perturb it. Then you go back and see it. That’s the code of the geneticist. Of course, an animal behaviorist, an ethologist, would just watch. But I hang around with people who get excited by genes. They get excited when they can talk about genes.”
In the Hawaiian archipelago, sexual selection pressures have produced fantastic displays even among fruit flies. There are more than four hundred species of Drosophila in the islands, and they all descend from a few flies that blew in on a freak wind millions of years ago, possibly from a single pregnant Eve. Being lovers of dew, the fruit flies live mostly in the rain forests on the cool green windward sides of the volcanoes. The picture-winged Drosophila are some of the most striking-looking—big for fruit flies, six to eight millimeters long—and their courtship is striking too. Courting males fly to a solitary spot on a tree trunk or a large leaf or fern a few feet above the ground. As many as ten males, sometimes from three or four different species, stake out different fronds of the fern or scales of bark or petals of an orchid. This kind of courtship is known as “lekking”: male fruit flies’ equivalent of hanging out at the 7-Eleven. They do wait around almost from seven to eleven—from sunrise to sunset, even through light rains. Males of some species stay motionless; others perfume their spots with tiny anal droplets of male pheromones as advertisements for themselves. Female picture wings are not ready to mate until they are a month old, and they often live another month after that, and they mate only once. So each female takes her time flying from lek to lek, day after day, sometimes for weeks, before she settles down to court and be courted.
Close up, males of each species court in their own way, according to the drosophilist Herman T. Spieth. A male Drosophila ornata stands directly behind the female with his head under her wing vanes, extends his proboscis, alternately stamps his forelegs against the fern, spreads his wings, straightens his abdomen, elevates the tip, and pulsates an anal droplet. After that, he goes into routines and subroutines. For instance, if the female kicks rearward with her hind legs, Spieth says, the male typically backs away several millimeters, spreads his wings horizontally to forty-five degrees, and exposes certain selected segments and membranes. The male sometimes courts from in front, and there his routine is completely different, including many ritual pawings of the fern, curlings of the abdomen, and what Spieth describes clinically as “contact of the labellar lobes,” explaining, in parentheses, “(kisses).”
Drosophila hamifera has a different display, including wing vibrations and Elvis-like gyrations of the abdomen. “If the female responds by making labellar contact (kissing), the male then circles rapidly to her rear.” There he assumes their species’s ritual position, says Spieth. He puts his head under her wings, holds on to her with his hypertrophied labellum (swollen lips), thrusts his forelegs under her abdomen, and moves them alternately to and fro.…
And so on: innumerable distinct routines and if-then subroutines in a single group of flies on a single isolated group of islands. Many of these pieces of behavior may have evolved the way the flies in Benzer’s Fly Room evolved, bit by bit, with changes of one letter or a few letters of genetic code at a time. The routines help the males do what the humpback’s songs and the bowerbirds’ bowers do: advertise a male as a good choice and set him apart from the rest of the lek. And a surprising number of the Hawaiian fruit flies’ routines include a moment in which the female, after a period of ritualized dodging, stabbing, darting, stamping, fanning, or apparent indifference, will march forward head to head “with the labellar lobes open and firmly ‘kiss’ the male’s open labellar lobes.”
After the female copulates with the male, she takes off and never sees him again.
“SURPRISINGLY,” says Michael Ashburner, who is a world authority on Drosophila at Cambridge University, “most entomologists don’t regard Drosophila melanogaster as an insect.” Ashburner laughs. “Well, it is, but because the literature on Drosophila is so huge and a lot of it requires you have some understanding of formal genetics and most insect biologists don’t, they’re scared of it, basically.”
Nevertheless, Drosophila melanogaster is made of the same stuff as other insects. Put a virgin female and a male Drosophila melanogaster beneath a large watch glass, and the action runs much the same course again and again, more or less like clockwork. The male sees the female, and even if he has never seen a female fly before in his life—even if he has never seen another living thing in his life—he seems to experience, as Benzer puts it, “an immediate ‘aha!’ reaction,” a fly Adam noticing Eve. Within seconds he maneuvers so that he is facing her head from one side. Then he holds out one wing toward her in a kind of salute and sets it vibrating: the love song of the fly. Hurrying around to her other side, he holds out his other wing toward her and vibrates that: second verse, same as the first. To Benzer in his workroom in the middle of the night, the song was just barely audible if he lowered his ear to an open vial: Eine Kleine Nachtmusik. The song of the fly does not sound romantic to a human ear, but then the fly seems unmoved by human songs that blast from the radios, tape decks, and CD players in the Fly Rooms. When Benzer played the fly’s love song at lectures, he used to introduce it with P. T. Barnum—style blarney: “You are privileged to hear a recording of the male courtship song of Drosophila melanogaster, and I hope the ladies will control themselves.” He enjoyed pointing out that at the female fly’s antenna, which is a sound-receptive organ, the love song has a volume of about one hundred decibels, which is comparable to the climax of the “1812 Overture.”
The male fly does not just shake its wing at the female at random. Drosophila melanogaster is thought to have evolved in Africa and must have had to set itself apart in those rain forests just as much as drosophilids did in Hawaii. If a male melanogaster does not sing just the right song, a female will emit a counterbuzz, a rejection buzz, which is an international fruit-fly message that males of every species seem to understand. Sometimes she will bat him away during his performance or extrude her ovipositor in his face, a sight that seems to have a discouraging effect. But if the male is singing her song and if she is a virgin, the rest of the action proceeds in the distinctive melanogaster series of steps, which are, as Benzer says, “only too embarrassingly anthropomorphic.” The male has an erectile penis. The female has a vagina. Copulation typically lasts twenty minutes. (“How anthropomorphic can you get?”)
Courtship and copulation are behavior of a higher order than the kind of behavior that is driven by clock genes. Courtship requires a whole series of complicated steps, a long chain of different pieces of behavior, and each step makes the next step more likely: One thing leads to another, as we say. Flies inherit every step in this dance. When a male courts a female, first he taps her with his foreleg, as if to get her attention. Then he follows her around, and starts singing. After the song, he sticks out his proboscis, as if to ask, Do I really want this? Is this female? The right species? He kisses her, licks her, and finally attempts to copulate. Richard Feynman invented a way of drawing the interactions of subatomic particles with arrows to show them approaching each other, and more arrows to show the parting of the ways. Back in the days when Benzer still thought of flies as simple particles of behavior, he sometimes drew the flies’ sequence of courtship steps in the style of a Feynman diagram with a helix in the middle. It was a joke in the same spirit as his countercurrent machine—describing living things as particles of behavior—but of course courtship and copulation are behavior of a much higher order than the behavior of particles. And again, the fly inherits all of this behavior along with its body. Behavior is part of the package.
Benzer could not imagine an instinct more interesting to investigate, and he thought that with genetic dissection he might be able to tease apart the steps. “The trick is designing a screen,” explains Ashburner of Cambridge. Benzer’s countercurrent machine was an ideal screen for phototaxis, Ashburner says (“Very, very simple but very elegant.”). His flight tester was an ideal screen for flight mutants (“Again simple but elegant.”). Screening for time-blind mutants was a little harder, because one had to figure out a way of checking thousands of flies for a fly that had a weird sense of time. “But Ron Konopka did that,” says Ashburner. “And damn painful some screens can be! And there are still aspects of complex behavior which are extremely difficult to—to—to—I mean, just logistically difficult to get mutants in. Certain aspects of sexual behavior, where you have the males posturing to the females. Or licking her bum, or whatever. You know. You could imagine you could do it, but I mean in technical terms it would be logistically an horrendous task to—”
In 1971, the year Benzer and Konopka published their discovery of clock genes, Jeff Hall joined the laboratory as a postdoc and began trying to figure out how to screen for mutants of courtship and copulation. Of all Benzer’s students, Hall was the one with the deepest background in Drosophila. He had been working since his undergraduate days with fruit flies, fly bottles, and funnel-in-beer-bottle morgues. Hall and Benzer decided that the simplest way to go into the problem would be to screen for what Hall was soon calling, in an ironic and rueful tone he learned from Woody Allen, savoir-faire mutants, flies that have no luck in love. To find them, Hall borrowed a set of mutants from another fly laboratory—a line of mutants in which the males never fathered any children. Hall put these males together with normal females and watched to see what would happen. The males could sing the love song of the fruit fly and they could follow it up—they could talk the talk and walk the walk—but they were sterile. They had defects in their reproductive systems.
Those were not very interesting mutants. They were as boring as flies with blind eyes or bad wing muscles. On the other hand, Hall could not help feeling impressed by the power of the instinct these flies had inherited. He had assumed that a blind fly, for instance, would be a savoir-faire mutant. But in a fly bottle a blind virgin male raised in total isolation can find a virgin female, even if she is blind too. Apparently he sniffs out her aphrodisiacal advertisements, her pheromones. The two mutants meet and pass on their genes.
Hall had also assumed that if a male could not fly he would not be able to hold out his wings and make the fly’s tremble song. But even the flightless mutants that Benzer found in the bottom of the flight tester were willing and able to sing a love song down there. When these flightless mutants spy females, Benzer says, they vibrate their wings “in a quite normal way, yet, when dropped off the end of a rod into open space they just clunk right down to the top of the table.” Once, years later, a student in Hall’s laboratory made male double mutants that could neither see nor smell. Then he cut off their wings. He introduced them to female double mutants that could neither see nor smell. A few of the double mutants still mated.
EACH TUFT of grass brings forth seed “after his kind,” as it is written on the first page of the Book of Genesis. Every life-form brings forth “after his kind,” the great whales in the waters and the birds above the waters. And every living thing that swims, creeps, or flies bequeaths to the next generation not only the form of its kind but also the instincts of its kind, including the instinct of generation itself: “And God blessed them, saying, Be fruitful and multiply, and fill the waters in the seas, and let fowl multiply in the earth.” This has always been one of the primary miracles, the burden of the first page.
Benzer and his students were trying to find a point of entry into these instincts by looking for places where the instincts had gone off on a new bent. Sometimes they noticed mutant flies that were half male and half female. Years before, Morgan’s Raiders had noticed these flies too. They are called “gynandromorphs,” from the Greek gynē, meaning “woman,” and andr, “man”: morphs of male and female. In some gynandromorphs the right half of the body is male and the left half is female. Every cell in the male half has one X chromosome and every cell in the female half has two. In some gynandromorphs—gynanders for short—the split runs down the middle, passing right through the head: the right eye is male, the left eye is female. In other gynanders the sexual border cuts across the body on a diagonal. The female melanogaster is bigger than the male, so the female parts of the gynandromorph are bigger than the male parts. Also, a female melanogaster’s abdomen is brown; a male’s is black (melanogaster means “black belly”). So the gynanders abdomen is a motley brown and black. “Glory be to God for dappled things,” the poet Gerard Manley Hopkins wrote, praising “skies of couple-color as a brinded cow,” “landscapes plotted and pieced,” “all things counter, original, spare, strange.” Of all things counter, original, spare, and strange, the gynander is one of the strangest—maybe too strange for Hopkins.
Sexual mosaics. Notice the mismatched eye colors and wing sizes. From Sturtevant, “Origins of Gynandromorphs.” (Illustrations credit 9.1)
To Benzer, gynanders were novelty-shop items. He once made a gynander with one good eye and one blind eye and put it into a vertical tube with a lightbulb overhead. A normal fly with two good eyes will climb straight up a tube toward the light. It will also climb up if the room is dark, because Drosophila has a sense of gravity as well as a sense of sight. But if Benzer turned on the light, his gynander would climb the tube in a corkscrewing path, because it would keep turning itself to one side, cocking its bad eye toward the light, trying to balance the input from the two sides of its head. If its right eye was bad, the gynandromorph traced a right-handed helix; if the left eye was bad, the gynandromorph traced a left-handed helix. “Sometimes,” Benzer wrote, “it is difficult to resist the temptation, out of nostalgia for the old molecular-biology days, to put in two flies and let them generate a double helix.”
Decades earlier, Sturtevant had realized how to use gynanders to make a form of what embryologists call a “fate map,” a map of the fate of every point in the early embryo, showing which part of a fly develops from each cluster of cells. At a very early embryonic stage called the blastoderm, a fly egg is covered with a smooth layer not of shell but of cells, ten thousand cells. In a gynandromorph embryo, half of these cells are female and half male. Gynander eggs are like Easter eggs in which each and every egg has been hand-dipped into two bowls of dye. The sexual boundary line may run crosswise, slantwise, any which way across the gynander egg, but it divides the surface into two parts, male and female.
Sturtevant had once worked out a way to trace the male and female parts of each gynander back to its point of origin on the surface of the blastoderm. To try out his idea, he had examined 379 gynandromorphs of Drosophila simulans, a close cousin of melanogaster. He had drawn pictures of each one, and noted which part of each was male and which female. Then he had put these sketches away and gone on to other projects. In 1969, two fly men—one of them a postdoc of Sturtevant’s student Ed Lewis—borrowed that now yellowed sheaf of drawings and used them to finish the project. They drew an oval map of the blastoderm’s surface and plotted the point of origin of the first left leg, the second left leg, and the third left leg; the head, the eyes, and the wings; the sections of the dorsal and ventral abdomen.
Sturtevant was dying while they worked on the fate map. They finished it just before he died.
Next, Benzer and Hotta made a fate map of the melanogaster egg. Like many of Sturtevant’s friends, they had always regretted that the map unit of genetics is named after Morgan and not after the man they called Sturt. To honor Sturtevant’s memory, Benzer decided to measure distances on his fate map in sturts. The distance from the point of origin of the fly’s first left leg to the point of origin of the fly’s second left leg, for instance, is ten sturts. Benzer could not quite pronounce the name of the new map unit without giggling. “But, you know,” he says, “that was a sentimental thing with me, naming it after Sturtevant.”
Now Benzer’s postdoc Jeff Hall began using gynandromorphs and fate maps to explore sexual instincts. He and another postdoc in the Benzer lab, Doug Kankel, knocked out a gynander with ether, mounted it in a kind of white goop (one brand name is Tissue-tek), and deep-froze it. Then, with a microtome, they sliced it into thin sections—so thin that they got as many as thirty or forty slices from a single fruit fly. They stained each section in such a way that the male cells stayed colorless, while the female cells turned dark brown. By looking through the microscope at these stained sections of the fly’s brain, Hall and Kankel could see which pieces of the nervous system were male or female, right down to individual neurons. In this way Hall would later map the portion of the brain that has to be female if a fly is going to elicit courtship from a male, and he also mapped the portion of a fly that must be male (a spot in his midsection) if he is going to try to copulate with her. Even if the cuticle of a gynander’s head is female, with female eyes, female ears, and a female head capsule; even if she has a female thorax and a female thoracic ganglion; and even if her wings are female, she will still hold out her wing and make it tremble in the love song of the male fly if just one critical focus inside her brain is male. On the other hand, a gynander with a body that is almost all male will still be receptive to a male’s song and dance if just one critical focus in its brain is female.
A fate map. This egg-shaped object is a fly embryo at the early stage called the blastoderm. Benzer’s diagram shows how each part of the adult fly comes from a specific site on the blastoderm’s surface. After making this fate map, he and his students traced pieces of behavior back to the surface, too, including many of the dance steps of courtship and copulation. From Benzer, “Genetic Dissection of Behavior.” (Illustrations credit 9.2)
Benzer could add each of these pieces of behavior to the fate map the same way he and his students mapped each piece of anatomy. Each week, their egg-shaped fate map was decorated with more landmarks of anatomy and behavior, all inscribed in the same spidery, dead black lettering that Benzer had used since Arrowsmith.
The project mattered as a way into the strange territory between genes and behavior, territory that would come to absorb Benzer more and more deeply. In a sense, the territory defined what was original about his project. Animal breeders and ethologists could see that instincts pass on from generation to generation. But only molecular biologists could go inside and see how the path from gene to behavior begins inside the embryo.
At that time the way an embryo grows and develops (a subject known to biologists simply as development) was still a complete mystery. The rules and origins of development were as obscure as the rules and origins of behavior. No one knew where to search for answers, and no one even knew what the answers should look like. Genes linked with the early development of the embryo had been on the maps for sixty years by then, but the problem was essentially imponderable. No one realized that the genes that Ed Lewis was mapping in Sturtevant’s old lab space would crack open the problem.
Lewis had arrived at Caltech in 1937 to write a Ph.D. thesis under Sturtevant. Ever since 1937 he had been sitting in the same Fly Room working on a few particularly bizarre lines of mutants. One was bithorax, which has an extra set of wings: a four-winged fly, first discovered in a half-pint milk bottle in 1915. Another mutant was Antennapedia, which has legs growing out of its head where its antennae should be. By the 1970s, after examining and crossing hundreds of thousands of deformed mutant flies, Lewis had begun to understand something about the roles that bithorax and Antennapedia play in the fly’s development. These genes control the body plan of the back half of the fly, everything below the head. Slowly, without publishing much of his research, Lewis mapped the genes in a great mural on his lab wall, and generations of Caltech administrators let him keep at it. “In any other institution—” Benzer would declare decades later at a rollicking campus party in Lewis’s honor, in front of snapping, clicking, and whirring cameras, after the world had finally caught up with Lewis’s work. “In any other institution—” By then Lewis had long since retired from teaching, but Caltech had allowed him to keep his old laboratory. He still worked almost as hard as ever as the Thomas Hunt Morgan Professor of Biology, Emeritus. Only a school devoted to pure research and to the memory of T. H. Morgan would have allowed Lewis to peg away decade after decade while he mapped bithorax. It was a project that sounded quintessentially irrelevant and proved central—like Benzer’s.
In a normal fly, the thorax has three segments. The first segment has a pair of legs. The second segment has a pair of legs and a pair of wings. The third segment has a pair of legs and a pair of balancers, called halteres. Lewis discovered that bithorax’s problem is not a single mutation but a cluster of mutations on the third chromosome. In a fly embryo these mutations confuse the identity of one segment with the identity of the next. When Lewis mapped them patiently decade after decade, he found that the genes in the bithorax complex are arranged in the same order along the chromosome as the parts of the body they affect. That is, if one goes down the chromosome from top to bottom, one comes to genes that affect the growth of the fly from the top of the head to the tip of the abdomen. The genes that control the development of the head and the antennae are at one end of the complex, and the genes that control the development of the tip of the abdomen and the anus are at the other end. What is more, these genes turn on one after the other as the fly embryo is growing, in anatomical order, beginning with the head and working down toward the anus; and if they switch on in a different order or if one of them misfires, the body plan of the fly is disarranged. In this sense, the fly itself is a map of its genes. As one drosophilist writes, “It is as if the insect’s entire body is the expression of a giant chromosome made visible to the naked eye.”
This complex of genes would eventually lead molecular biologists inside the problem of development the way Benzer’s mutants would lead them inside the problem of behavior. What Lewis found in flies would turn out to be fundamental throughout the tree of life. New tools of molecular biology would augment the old tools of genetics and mapping to produce breakthrough after breakthrough; and the same tools would work equal wonders with Benzer’s mutants. Clock mutants and the savoir-faire mutants would provide the first set of picture windows into the workings of genes and behavior at the level of the anatomies of atoms.
In the last years of the century, Lewis, standing by his old teacher Sturtevant’s iris bed or besieged by reporters in the faculty parking lot, would say with a grin, “It was pure genetics. It was pure genetics.” Nothing molecular about it. He would remember how Delbrück had pounded the table and denounced the fly, and he would murmur, so softly that the reporters had to ask him to raise his voice, “I’m glad I stayed with it.”
MEANWHILE, Jeff Hall accumulated a shelf of bottles of mutants with interesting courtship problems. One mutant male courted vigorously but never copulated. Hall named him celibate. Another male mutant disengaged after only about ten or twelve minutes and rarely fathered any children. Hall named him coitus interruptus. Then there is stuck, which was discovered in another fly lab. A stuck male has trouble withdrawing his penis after copulation. “The pair just sticks together,” Benzer says, “and they keep pulling against each other for hours or days on end. Sometimes they die of starvation.”
In the wild, of course, a mutation like stuck could not last long. A male that is stuck will not pass on his genetic inheritance. But this particular mutation is recessive, which means that flies with one mutant copy and one normal copy of the gene can court and mate normally. In the Church Laboratory, Benzer and Hall began collecting and breeding these courtship mutants, keeping them going from generation to generation like seedless grapes.
The most surprising courtship mutant was discovered at Yale. A graduate student in a Fly Room there was studying the process of egg formation. He zapped flies with X rays and looked for sterile female mutants. In his fly bottles he happened to notice a few mutant males that were courting each other. Ordinary males will bump and bustle and dodge around other males in a fly bottle or a petri dish without ever touching one another for long. Watching them is like looking down at a sea of strangers in Penn Station. If two males do collide in the crowd, they may retreat a step or two and begin grooming themselves, almost as if they were embarrassed, like two cats. If a normal male sees another male approaching him with a wing out, he starts flicking his own wings violently in rejection. But these males at Yale sang to each other. Tests showed that their sperm was healthy and that they would court females but would not copulate. They would go through all the steps of foreplay, but the last step they would not do.
Sometimes three males, or five, ten, or more would form chains and follow each other around in the fly bottle in long, winding conga lines. They would chain for hours. They tended to stay down around the food at the bottom of a bottle, but when the dancing had reached a certain pitch of frenzy they would get right up onto the glass walls of the bottle and chain. Often they broke up and then came back together. They took little breathing spaces and went right back to chaining.
Those who have worked with this mutant have found that food is important: Giving the flies good food and keeping them at a nice warm constant temperature seems to encourage chaining. “Sometimes it takes a few days,” one technician says. “It’s like a social thing. They all get to know each other.” The food, the climate, and perhaps the social environment have to be right. “When they are really happy,” she says, with a half-apologetic smile for talking about the happiness of flies, “then you get these chains.”
The investigator at Yale published a note about this mutant, which he named fruity. Then he went back to his home country, India, where he was never heard from again, and fruity was left an orphan. When Hall read about it, he decided that this was the quintessential courtship gene. He sent to Yale for a bottle of fruity, although he decided that the name had to go. He chose fruitless.
In Dante’s vision of the tenth circle of Hell, sodomites go round and round with their bodies linked in a wheel, circling on burnt sand in a whirl of ever-moving feet. In Benzer’s Fly Room, the scene looked like Dante’s. The male mutant flies whirled in bottles and petri dishes and test tubes—long swirling sinuous chains, males only, winding their way around and around, hour after hour. The males never tried to copulate. They only formed these long conga lines in their milk bottles and test tubes and danced, sometimes sticking out one wing and singing the love song of their kind while they danced, as if they were shaking a tambourine.
In the 1970s, most aspects of sexual behavior were still a black box, at the level of atoms, molecules, and genes. Biologists had collected observations of sexual behavior in tens of thousands of species. The importance of the instinct, which is after all indispensable, and the phenomenally variable behavior of closely related species like Hawaiian Drosophila suggested that in most cases every step of the instinct must be inherited. And for the atomic theory of behavior, fruitless would provide the first way in.
The fruitless males chained on the floor of their bottle. They chained on the sides of the glass in big wheels and zeroes all day long, more and more of them spiraling up the walls toward dusk. And when Jeff Hall dumped them out of their bottle, he could see them chaining all the way down the funnel, chaining into the morgue.