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Like a little white Lazarus with red eyes, the paralyzed mouse was walking again. A few days earlier, the mouse had been sprawled on an operating table while two Chinese graduate students peered through a microscope and operated on its spine. With a tiny pair of scissors, they removed the top half of a fingernail-thin vertebra, exposing a gleaming patch of spinal-cord tissue. It looked like a Rothko, a clean ivory rectangle bisected by a red line. Cautiously—the mouse occasionally twitched—they snipped the red line (an artery) and tied it off. Then one student reached for a $1,000 scalpel with a diamond blade so thin that it was transparent. With a quick slice of the spinal cord, the mouse’s back legs were rendered forever useless. Or they would have been, except that the other student immediately doused the wound with a faintly amber fluid, like the last drop of watered-down scotch. The fluid contained a chemical called polyethylene glycol, or peg, and as the students stitched the mouse back up, the chemical began to stitch the animal’s nerve cells back together.

Two days later, the mouse was walking. Not perfectly—its back legs lurched at times. But compared with a control mouse nearby—which had undergone the same surgery, minus the peg, and was now dragging its dead back legs behind itself—it puttered around brilliantly, sniffing every corner of its cage. If peg ever proves effective in humans, it will be a near-miraculous therapy: Despite spending many millions of dollars on research over the past century, doctors have no way to repair damaged spinal cords. But that’s not the only reason the man directing this research—a surgeon in Harbin, China, named Xiaoping Ren—has been garnering attention in scientific circles. Repairing spinal cords is just one part of a larger, much more audacious project that Ren and a surgeon in Italy are leading. Clues to their plan can be seen on the walls of Ren’s lab. Had the mouse on the operating table raised its red eyes, it would have seen three seemingly unrelated posters. The first shows two mice: a black mouse with a white head and a white mouse with a black head. The second shows a monkey with thick zigzag stitches circling its neck, like a choker necklace. The third shows a tiny Russian man in a wheelchair. The common connection is their heads. The half-black/half-white mice look Photoshopped, but in fact Ren’s team surgically switched their heads, decapitating each mouse and grafting its head onto the body of the other. The monkey poster is the “after” shot of a primate head transplant performed in Ren’s lab in January. And now Ren is preparing to perform a head transplant on another primate, a human being—and the Russian in the wheelchair has volunteered to go first.

Building No. 8 at the Harbin Medical University hospital in northeastern China, where Ren has his office, is not a serene place. Farmers pour in from all over Heilongjiang province for treatment, sleeping on mats and smoking in hallways, washing clothes in sinks and drying them on radiators. By 8 a.m., patients are lined up dozens deep just to ride the elevators. Amid this chaos, Ren comes off as quiet, even timid. But there’s nothing timid about his approach to surgery. He was born in China in 1961 and lived there until his mid-30s, when he moved to the United States. In 1999, he worked on the team in Louisville, Kentucky, that performed the world’s first successful hand transplant. In preparation, he practiced the surgery on pigs, switching forelimbs between different animals. He returned to China in 2012. Ren keeps a bronzed-pig-ear trophy from the Louisville team in his office; the inscription reads, “We couldn’t have done it without you.” Ren’s work on head transplants is part of a long, if fringe, tradition in his profession. A surgeon in St. Louis, Missouri, created the world’s first two-headed dog back in 1908, by grafting the head of one pooch onto the neck of another. Soviet and Chinese surgeons duplicated the feat in the 1950s; one Soviet dog lived for 29 days, and it could lap water with both of its heads. The Chinese surgery took place at Ren’s university, and a mural of the bicephalic beast graces a wall in the library.

In the 1970s, a Cleveland, Ohio, surgeon named Robert White transplanted the heads of several rhesus monkeys onto others’ bodies; his staff reportedly cheered when the first one woke up and tried to bite someone’s finger. White didn’t attempt to reconnect the monkeys’ spinal cords (he focused on keeping their brains alive), so no one knows whether they could have walked or moved their arms. But they did eat and track objects with their eyes, and their brain waves appeared normal. White was an eccentric who sometimes smoked a pipe while operating, and he spent the next few decades making sporadic talk-show appearances and trying to drum up support for human head transplants. He even traveled to Kiev, Ukraine, in the 1990s to meet with interested doctors there, but nothing came of his efforts—a fact that Ren rues. “We’re stuck where we were 40 years ago,” he told me, with no way to treat muscle- and nerve-wasting diseases, paralysis, or other body-wide malfunctions. “If we don’t do this work, then 20 years, 100 years, 200 years from now, we’ll still be here.” White’s trip to Ukraine did accomplish one thing, however: It captivated a crippled boy named Valery Spiridonov—the Russian on the poster in Ren’s lab. Spiridonov, now 31, has Werdnig-Hoffmann disease, a genetic disorder that wastes away muscles and kills motor neurons—nerve cells in the brain and spinal cord that help move the body. He has no memory of ever walking, and his movement today is limited to feeding himself, typing, steering his wheelchair with a joystick, and little else. He sits with his right leg perpetually crossed over his left, and his body below the neck looks shrunken, almost deflated. His condition is fatal, but there’s no telling how much time he has left—according to doctors, he should have died long ago.

Spiridonov is a tech geek; he runs an educational-software company from his home in Vladimir, 120 miles east of Moscow, and closely follows news about exoskeletons and other bodily enhancements. During a Skype interview in February, he told me about a friend who, after losing an arm in an industrial blender, got outfitted with a robotic one. “He shows how much technology can change life to the better,” he said. Spiridonov pinned his own hopes on technology—specifically, radical surgery—after seeing White on television. “Removing all the sick parts but the head would do a great job in my case,” he remembers thinking. “I couldn’t see any other way to treat myself.” The operation would cost between $10 million and $100 million, depending on where it took place, and require 80 surgeons. Ren’s Italian partner has said it could happen as early as next year. Not surprisingly, many scientists and ethicists have slammed the project, accusing the surgeons involved of promoting junk science and raising false hopes. One critic even argued that the surgeons should be charged with murder if the patient dies—as he almost certainly would. But other researchers acknowledge that the project has a foundation, however shaky, in science. The past few decades have been a golden age of transplant medicine. New surgical techniques have made reattaching delicate structures easier, and powerful new drugs can all but eliminate the threat of rejection. In addition to hearts, livers, kidneys, and lungs, doctors can now transplant uteruses, voice boxes, tongues, penises, hands, and faces. Those last two are especially impressive considering all the tissues involved: muscle, skin, bone, tendons, cartilage, nerves, blood vessels. Ren sees head transplants as the logical next frontier. (Technically, the surgery would be a body transplant, since the acquisition of a new body is what saves the patient’s life. Then again, the head makes up less than 10 percent of our body weight. Can you really “transplant” the heavier, majority part? And if rejection occurs, it will be the body rejecting the head, not vice versa.)

Transplanting a head does, of course, present tremendous new challenges for surgeons. Unlike, say, fingers, which can survive for days detached from a body, brains suffer irreversible damage within minutes of losing blood flow. Cooling the brain can delay damage for up to an hour—just enough time, perhaps, to transplant a head. Doctors also need to test whether immunosuppressant drugs, which prevent the body’s immune system from attacking foreign tissue, will protect the brain as well as they protect other organs. But there’s no reason to think they won’t.

Perhaps the biggest obstacle is repairing the spinal cord so that the patient’s brain can control the new body. Nerves outside the spinal cord can regrow, which explains why hand and face transplantees can learn to chew and smile and twiddle their thumbs again. Cells within the spinal cord don’t grow back, but chemicals such as peg can fuse cells, breaking open their membranes and forcing them to glom together into a larger, hybrid cell. When applied to the severed spinal-cord stumps of rodents and dogs, the amber fluid can fuse nerve cells above and below the injury and thereby reestablish communication, however imperfect, between the brain and the lower body. That’s how the little Lazarus in Ren’s lab regained the ability to walk.

Two human cases provide additional hope. One involved a German woman who suffered a skiing accident; the other, a Polish man stabbed with a knife. Both were left paralyzed despite extensive rehab. But after undergoing experimental surgeries, each learned to walk again with a walker. Neither operation involved peg or a transplant—surgeons used tissue from the German woman’s abdomen and cells from the Polish man’s olfactory nerve to help their spinal cords heal—but they proved that human beings with severe spinal-cord injuries could, in certain circumstances, relearn to walk. One man who followed these developments closely was a neurosurgeon in Turin, Italy, named Sergio Canavero. Ever since hearing about Robert White 30 years ago, he’s been itching to try a head transplant himself, and these advances gave him a semiplausible scientific justification. He plotted out a procedure and announced his ambition in 2013, to near-universal criticism. He nevertheless began promoting the idea in the media and writing to like-minded scientists, including Xiaoping Ren. After appearing on television one day, he sat down at his computer to find an unsolicited email from Russia. Valery Spiridonov wanted to chat. Canavero, who is 51, has a shaved head and a crooked grin. He peppers his speech with cheesy slang (saying “bread” instead of “money”) and uses props like bananas and spaghetti to explain spinal-cord damage and repair. He sees head transplants as a step toward radical life extension for all human beings. Indeed, he nicknamed the surgery the “head anastomosis venture,” or heaven, with a nod toward death and resurrection. (Anastomosis refers to the surgical joining of two body parts.)

Canavero tends to make blowhard statements that denigrate his critics and magnify his own prowess, like a Mediterranean Donald Trump. “I’m into jujitsu,” he told me via Skype, “so I have the martial mind that you need to tackle all the morons that come with idiotic questions.” It doesn’t help his reputation that he compares himself to Dr. Frankenstein and makes flippant references to Josef Mengele, or that he published a seduction guide called Donne Scoperte, or Women Discovered.

More troubling are the rash, unfounded claims he makes about the likelihood of the surgery succeeding, and his habit of promoting his work largely through the media—a practice that most scientists consider unseemly, if not unethical. His critics describe him, on blogs and tech websites, as a “corrupt” and “delusional” liar “with a knife and a mad glitter in his eye.” He “glibly glides past major problems,” they say, with his “Human Centipede–level medical horrorshow.” His plan is insane, “like James Bond villain insane,” and will amount to “an elaborate act of slow torture and murder.” In brief: “Fuck Canavero.” Yet Canavero is an accomplished neurosurgeon who has published dozens of scientific papers, particularly on neurological pain. He has focused on head transplants since 2013, coordinating experiments with Ren and a South Korean surgeon, C-Yoon Kim, and laying out his vision of heaven in journals.

The surgery would begin, like most transplants, after a car wreck or other mishap that leaves a young man brain-dead. After getting his family’s permission, doctors would wheel him into the operating theater and prop him into a sitting position for his surgical decapitation. Meanwhile, a second team would anesthetize Spiridonov and pump his veins full of fluids at a chilly 50 degrees Fahrenheit. This would delay tissue death in the brain, but only for an hour at most—so the surgeons would need to move quickly to reestablish blood flow. They would cut just above Spiridonov’s collarbone, harvesting his trachea and esophagus but leaving his thyroid gland behind. They would also color-code his severed muscles, to make reattachment in the new body easier. Finally, the surgeons would cut both men’s spinal cords simultaneously, using a larger version of the transparent diamond blade in Ren’s lab. (The sharpness is crucial for preventing damage to nerve tissue and minimizing scarring.) One quick stroke, and they would sever the last physical connection between Valery Spiridonov and the body he was born with. Spiridonov’s head would float across the operating theater on a customized crane, hanging by Velcro straps. Now the transplant would begin. Whereas Ren’s team could swap the severed mouse heads with their hands, Spiridonov’s head would float across the operating theater to the donor body on a customized crane, hanging by Velcro straps. Surgeons would align the spinal stumps and bind the two ends together, using peg to fuse Spiridonov’s spinal cells with the donor’s. The surgeons would also implant an electrical paddle near the fusion site, because studies have shown that bursts of electricity help establish communication across a severed spinal cord.

At the same time, another team of surgeons would begin the long, messy process of attaching a head to a body. With the hour ticking down, establishing blood flow to Spiridonov’s brain would take priority. After that, surgeons would install the spinal bones, trachea, and esophagus, then attach the color-coded muscles. One vital step would involve connecting the nerves that carry signals from the brain to the heart and to the muscles that pump the lungs, so Spiridonov’s new body could breathe and regulate its heartbeat. Thirty-six hours after entering surgery, the new Spiridonov would roll out the door, sitting upright. Machines would breathe for him at first, and pump his blood. His head and neck would be locked in a cervical collar, and doctors would keep him comatose with barbiturates or other drugs. But after a few weeks, once doctors noticed signs of motor recovery, they would scale the drugs back and let him surface toward consciousness. The first sign of success would be Spiridonov opening his eyes or smacking his lips. But the doctors gathered around his bed would be watching above all for his fingers to curl or for his toes to flex—for any voluntary movement below the neck. For some sign that the brain’s motor signals—the electrical embodiment of Spiridonov’s will—were able to leap across the gap in his spinal cord and stir an alien body to life. Ren’s approach to the surgery differs somewhat from Canavero’s—as does his approach to science generally. He’s more cautious, and while he believes that Canavero is brilliant, his colleague’s antics seem to exasperate him.

For instance, Canavero claims that the surgery has a “90 percent plus” chance of success, and has promised Spiridonov the ability to walk and have sex afterward. Ren would never say something so definitive. Nor was Ren thrilled when Canavero released pictures of the monkey head transplant to the public. Ren doesn’t necessarily want to distance himself from that surgery; he even showed me the monkey’s skull in his lab—it’s brown and slightly sticky, with gristle still adhering. But he knows that primate work is sensitive, and the (mostly negative) attention the pictures garnered made his life harder. The surgeons also diverge on a timeline for the procedure. When Canavero first announced his plan, he said the surgery would take place in late 2017, probably in China. He would like to perform the operation around Christmas, because he thinks the symbolism—of heaven coming to Earth on or near that day—might help him drum up support. But Canavero has recently acknowledged that he and his team might need more time—largely because the Chinese government hasn’t given them the green light. Still, he insists they could pull off the surgery within two years of getting government approval, whether in China or another country. Ren, who’s running much of the actual research, refuses to commit to a date, saying that while late 2017 isn’t impossible, every preliminary experiment would have to go perfectly for the surgery to take place then. His team still needs to collect data from hundreds of mice, and conduct more large-animal transplants, probably with dogs. Ren also wants to choreograph the surgery with cadavers and, as a final test, swap the heads of two brain-dead donors. All of which takes time—months, maybe years. The preliminary work for the first hand transplant Ren took part in lasted two years, and that procedure involved 20 surgeons, not 80.

Spiridonov isn’t pushing for a quick surgery, either. His faith in technology—and in Canavero—seems unshakable, but it’s tempered with prudence: He says he didn’t sign up for “expensive euthanasia.” “Only when I see a moving, living monkey, a moving, living rat [that survives] the operation for several months, years maybe, only then will I do this,” he said. So far Ren’s team has performed animal head transplants only as proof of principle, euthanizing the creatures within a day. Future experiments will try to keep them alive longer. What’s more, neuroscientists have challenged every last step of heaven. To take a few obvious objections: peg can fuse animal nerve cells together, yes, but no one knows what percentage would reconnect in human beings. Moreover, no one knows how well those cells would function after fusion. And doctors would have no way to control which nerve cells peg fused together, so cells that originally controlled the legs might end up wired to the arms. This all assumes that Spiridonov wakes up, and that his brain—which hasn’t steered a walking body since he was a toddler—even knows what to do. Yet for every objection, Ren and Canavero can cite this or that study showing how they’ll overcome the problem. Some studies suggest that basic motor function is preserved if just 20 percent of certain cells in the human spinal cord remain intact. So peg could fail to fuse four of every five nerve cells and the surgery might still succeed. And the human nervous system might be somewhat plastic: In experiments on people with damaged arm nerves, surgeons rerouted a nerve from the chest into the biceps, and patients eventually learned to move that arm. With practice, the brain might overcome some mismatch among fused nerve fibers.

After reading enough scientific papers, you can see how Spiridonov—who has waited 20 years for this chance—could talk himself into the surgery. But while no single step in a head transplant seems outright impossible, each one remains fiendishly difficult, and the surgeons need to get all of them exactly right on the first try. It’s like an Olympic figure skater promising to do six consecutive triple axels and then nail a backflip. No matter how talented she is, you have to wonder. And really, discussing head transplantation as a technical exercise misses something crucial: Even if the surgeons can pull it off, should they? The week before I visited Harbin, a reporter in Hong Kong published a tabloid story that called Ren “China’s Frankenstein.” Before Ren agreed to talk with me, he pulled out a copy with several words and phrases highlighted in yellow. We had to go over each one and why he objected to it: gruesome, secretive, abhorrence, not interested in ethics. The article seemed to obsess him—he brought it up eight times over the next few days. Given such hostility toward the project, even those only peripherally involved with it remain wary. When Canavero and Ren submitted three papers on brain preservation and spinal-cord fusion to the journal Surgery last fall, Michael Sarr, Surgery’s co-editor and a retired Mayo Clinic surgeon, took the unusual step of polling the journal’s editorial board before considering them. One-third of the board voted to reject the papers, but one-third wanted to accept them. (The final third was neutral.) Surgery did run the articles, in July—but only to explore the technologies involved as a potential treatment for traumatic spinal-cord injuries. That is, the journal did not want to come across as condoning head transplants. “You can just imagine all the ethicists going nuts over this,” Sarr told me.

It wouldn’t be the first time: Nearly every new type of organ transplant in history has met stern (and sometimes hysterical) opposition. Canavero may seem reckless, but Christiaan Barnard, a South African who performed the first human heart transplant, technically killed the first donor, a brain-dead woman, by taking her off life support without her family’s permission and giving her an injection of potassium to render her legally dead. The recipient survived for just 18 days. Richard Lawler, who performed the first kidney transplant, was shunned in certain circles and endured rebukes from a national urological organization, even though the surgery succeeded. More recently, face and hand transplants polarized the surgical community. Critics argued that such procedures were unethical because they wouldn’t save lives, and recipients would have to take immunosuppressant drugs that would raise their risk of developing diseases. A few prophesied dire social consequences of face transplants: donor families stalking recipients, and markets emerging to buy and sell comely faces. But face and hand transplants proved quite successful, with few downsides. James Giordano, a neuroscientist and neuroethicist at Georgetown University, doesn’t think the head-transplant surgery will succeed—or even come close. But he says it’s important to consider the historical context when thinking about the ethics of the procedure. “I see this as being representative of much of the trajectory of very rapid experimental medicine,” he told me. “There are those who look at this and say, ‘This is cowboy medicine. This is Wild West. This is so avant-garde. This is so bizarre.’ No. It’s really not that bizarre.” Or at least no more bizarre than heart and kidney and face transplants once seemed. “This is something we’ve been flirting with for a long time.”

Perhaps most important to Giordano is the fact that Spiridonov has no other treatment options and has given informed consent to go under the knife. “One could look at this patient in two ways,” Giordano said: “as an idiot or as an astronaut.” Either way, Spiridonov knows the risks and can back out at any point, which to Giordano goes a long way toward justifying the surgery on ethical grounds. Of course, many ethicists disagree with this assessment. “Just because somebody consents to harm, that doesn’t necessarily give a physician the right to harm the individual,” Assya Pascalev, a philosophy professor and bioethicist at Howard University who studies organ transplants, told me. “My consent to slavery doesn’t allow you to enslave me.” One young man—whose organs were riddled with metastasized tumors—took a train 1,100 miles just to knock on Ren’s door in Harbin and beg to go first. The cost of the surgery also raises concerns. Twelve thousand people suffer spinal-cord injuries in the United States alone each year, yet few of them would be eligible for head transplants. They don’t need new bodies so much as a way to mend their broken ones. Why not channel the many millions that the head transplant would cost toward a treatment that would help more people? Canavero argues that perfecting head transplants will allow his team to cure spinal-cord paralysis as well, almost as a side project, but one critic compared that to promising to build intergalactic spaceships before we’ve even landed on Mars.

The Russian government has not agreed to pay for the surgery, so Spiridonov is seeking donations and selling hats, mugs, T-shirts, and iPhone covers online to raise money; they’re emblazoned with a logo of his face and a new body, including a beefy biceps. But sales have not been brisk, and Spiridonov knows he won’t be able to raise enough money himself. Canavero hopes to partner with researchers in the U.S. to win a $100 million grant from the MacArthur Foundation. Barring that, he plans to ask tech billionaires such as Mark Zuckerberg to “fork over the bread” for the surgery. If that doesn’t work, Spiridonov could lose his place in line to a Chinese patient, especially if China’s government funds the project. Ren says about 10 prospective patients have approached him. One young man—whose organs were riddled with metastasized tumors—took a train 1,100 miles just to knock on Ren’s door in Harbin and beg to go first. Even the fact that the surgery might take place in China concerns some ethicists. China allows scientists more latitude in medical research than Western countries—it has far fewer restrictions on cloning, for instance, and scientists there recently suffered a hail of criticism for genetically editing human embryos (albeit nonviable ones) with a technology called crispr. Some Western scientists applaud this lack of squeamishness. But China has a reputation for, among other things, harvesting organs from executed prisoners. (Recent laws have purportedly curbed this practice.)

Pascalev told me a head transplant would not win approval in the United States or Europe if proposed today. And in theory, when Western scientists operate abroad—Canavero is European; Ren is a naturalized U.S. citizen—“the Western, higher standard and regulations apply,” she said. But “oversight and enforcement are different abroad, as is the culture. So it comes down to the researcher’s conscience.” Ren’s and Canavero’s consciences are apparently clear. In the stark math of transplant surgery, they argue, when you have two people all but certain to die, why not try to save one? If successful, head transplantation will reignite centuries-old debates about the relationship between mind, brain, and body. Is the you inside you situated inside your brain alone? Or does personhood depend on the specific mound of flesh you call your body? The surgery would also raise social issues. The body alone produces eggs and sperm, so any children that head transplantees have after surgery would not be related to them genetically. But they would be related to the body donor’s family. Would the biological relatives have visitation rights, or the standing to contest the child’s will? Would the transplantee’s spouse be committing adultery whenever they made love? Inversely, would the donor’s spouse long for one last embrace—or grow jealous of the new person having sex with their spouse’s body? The most profound—and unanswerable—question is whether the transplantee would still feel like himself after surgery. For all their medical value, animal studies offer no help here. We can monitor an animal’s brain activity and get some sense of how things are going upstairs, but beyond that, we’re at a loss. Is the animal content, confused, suffering? Ren declined to speculate with regard to the creatures in his lab. But he did show me an unreleased video of the monkey head transplant, and I can say that after the surgery, the monkey didn’t appear to be thinking (or feeling) much of anything—he blinked when someone prodded his eyes with forceps, and Ren said he could bite as well. But otherwise he looked catatonic. When I asked how long the monkey lived after the surgery (some sources say 20 hours), Ren stopped the video and pulled out the tabloid article again.

In studying the psychology of head transplants, then, scientists are forced to fall back on imperfect proxies. Some research suggests that the human brain can readily adapt to a new physical form. Through clever experiments with mannequins and helmet cameras, neuroscientists can induce out-of-body experiences in volunteers and create the illusion of swapping them into a body of a different size or sex. Some experiments can even make people feel like they have three arms or foot-long Pinocchio noses.

Then again, those bodily manipulations occurred in a lab, not the real world, and they lasted just minutes. Other evidence suggests that our physical sense of self isn’t so plastic. Many amputees experience phantom limbs, the ghostly presence of a lost arm or leg. People can also experience phantom teeth, breasts, uteruses, penises, and colons (complete with phantom flatulence). This implies that the brain has a hardwired internal representation of the body—a mental scaffold that resists radical change. More disturbing, phantom limbs often produce real pain—cramps, stinging, an unquenchable burning. Canavero, a specialist in neurological pain, feels confident that he can alleviate such problems, but if Spiridonov wakes up from the surgery, he could well experience an agonizing, full-body phantom. Perhaps most intriguing, a new body could affect higher-level brain function. The body might have different concentrations of hormones that affect sex drive and other appetites, which can be big components of personality. Some studies have linked testosterone and estrogen levels to differences in aggressiveness, impulsive behavior, and the tendency to take financial risks. Other research hints that gut bacteria—which can differ markedly from person to person—can manipulate our moods by releasing certain chemicals. Even memories could change. Consider a pianist whose most cherished moments involve playing Chopin. Those are embodied memories, residing partly within her hands, and they might vanish if she woke up with, say, an accountant’s body. The same goes for athletes: They rely heavily on what scientists call procedural memories (popularly known as “muscle memories”), which enable the brain and body to work together with precise timing. Having a new body would destroy that timing. Studies on athletes who suffer injuries and become paralyzed have found that many feel like different people afterward.

Indeed, all of us might feel diminished like this. Think about your most vivid memories—times of intense joy or shame or fear. Often you feel those memories viscerally, as a stab or a pang or a swell of pride in your chest. But those reactions probably wouldn’t be available after a head transplant, at least not at first, according to Pascalev, of Howard. “You’re used to having this stomach-churning experience or the butterflies,” she told me. “And it may not happen.” At a minimum, having another person’s body would be creepy—just ask Clint Hallam. The team that Ren worked with in Louisville can claim the world’s first successful hand transplant, but the first hand transplant ever took place in France, and Hallam was the patient. Before the surgery, he passed himself off as an Australian businessman who’d lost his right hand in a logging accident. In truth, he’d lost it in a circular-saw accident in a New Zealand prison in 1984, where he was serving time for fraud. Surgeons in Lyon spent 14 hours grafting a new hand onto his arm in 1998, from a dead motorcyclist. But having a corpse’s hand proved too unsettling for Hallam, and he stopped taking his immunosuppressants, forcing surgeons to re-amputate the hand in 2001. That procedure took 90 minutes. Nowadays, psychologists screen prospective hand and face transplantees for months before surgery, to avoid a repeat of the Hallam disaster. Therapists also provide crucial postsurgical support. But no amount of screening or therapy could prepare someone for a head transplant, which combines all the fraught identity issues of a face transplant with the excruciating rehab of a hand transplant. And head transplants aren’t reversible.

According to Pascalev, the human chimera that awoke from surgery wouldn’t really be the head donor or the body donor anymore, but someone else entirely. In that sense, a head transplant wouldn’t save Valery Spiridonov’s life so much as create a new one. A life with affinities to Spiridonov’s old one, certainly. But in many ways—medically, psychologically, maybe even spiritually—it would be something entirely new, unprecedented in history. “It goes beyond what we’ve ever contemplated,” Pascalev said. “And by ‘we’ I mean humankind.” Spiridonov doesn’t worry much about the risks, psychological or otherwise, of waking up with a new body. Perhaps inevitably, given his handicap, he equates his personhood with his brain alone. “For me, a body is like a machine, doing some duties or some regular stuff, just to support living,” he told me. The transplant “is not about philosophy; it’s about mechanics.” He seemed to think that acquiring a new body would be akin to getting a new wheelchair. Still, the constant media attention, and the uncertainty about when and where the surgery will occur, have taken an emotional toll. “I’m really, really tired of being famous,” he told me. “It’s exhausting, and it takes a lot of your time, for nothing.” He doesn’t fantasize much about having a new body, in part because he doesn’t know how much control he’ll have over it. Will he wake up from surgery like the mouse treated with peg in Ren’s lab—faltering a little, but able to move under his own power? Or will he be even worse off than the control mouse—unable to use any of his limbs, and shackled to an alien body? He does have one dream, though: to buy a motorcycle. He’s even picked out the model, a black 156-horsepower sport bike. He imagines cruising up the coast of California or Italy—riding tall in the seat instead of sagging low, the way he does now in his wheelchair. “I believe I will like this experience,” he said. Hearing his fantasy—of speeding ahead, a little recklessly—reminded me of something else he’d said. I’d asked whether the surgery scared him. After all, doctors won’t know what a head transplant feels like for the patient—whether it’s horrifying or exhilarating or somehow both at once—until they do one. No, he said, he wasn’t scared. “I’d like to be involved in something fast, and then we’ll see what it will come to.” He grinned. “Shoot first, then ask.”