Saturday, 17 April 2010

Johnald's Fantastical Daily Link Splurge

Johnald's Fantastical Daily Link Splurge

Why It’s So Hard to Tell Which Tooth Has the Ache

Posted: 16 Apr 2010 03:27 PM PDT


When it comes to a toothache, the brain doesn't discriminate. A new imaging study shows that to the brain, a painful upper tooth feels a lot like a painful lower tooth. The results, which will be published in the journal Pain, help explain why patients are notoriously bad at pinpointing a toothache.

sciencenewsFor the most part, humans are exquisitely tuned to pain. The brain can immediately distinguish between a splinter in the index finger and a paper cut on the thumb, even though the digits are next-door neighbors. But in the mouth this can be more difficult, depending where and how intense the ache is.

"We don't know much about tooth pain," comments dentist and neuroscientist Alexandre DaSilva of the University of Michigan in Ann Arbor, who was not part of the new research. The new study is one of the first to address the puzzle of toothache localization, he says.

In the study, researchers led by Clemens Forster of the University of Erlangen-Nuremberg in Germany analyzed brain activity in healthy — and brave — volunteers as they experienced tooth pain. The researchers delivered short electrical pulses to either the upper left canine tooth (the pointy one) or the lower left canine tooth in the subjects. These bursts of electrical stimulation produced a painful sensation similar to that felt when biting into an ice cube, Forster says, and were tuned such that the subject always rated the pain to be about 60 percent, with 100 percent being the worst pain imaginable.

To see how the brain responds to pain emanating from different teeth, the researchers used fMRI to monitor changes in activity when the upper tooth or the lower tooth was zapped. "At the beginning, we expected a good difference, but that was not the case," Forster says.

Many brain regions responded to top and bottom tooth pain — carried by signals from two distinct branches of a fiber called the trigeminal nerve — in the same way. The V2 branch carries pain signals from the upper jaw, and the V3 branch carries pain signals from the lower jaw.

In particular, the researchers found that regions in the cerebral cortex, including the somatosensory cortex, the insular cortex and the cingulate cortex, all behaved similarly for both toothaches. These brain regions are known to play important roles in the pain projection system, yet none showed major differences between the two toothaches. "The activation was more or less the same," Forster says, although he adds that their experiments might have missed subtle differences that could account for why some tooth pain can be localized.

Because the same regions were active in both toothaches, the brain — and the person — couldn't tell where the pain was coming from. "Dentists should be aware that patients aren't always able to locate the pain," Forster says. "There are physiological and anatomical reasons for that."

DaSilva agrees that the brain's inability to tell top-tooth pain from bottom-tooth pain "pairs really well with what we see in the clinic."

Understanding the pathway from tooth to brain may help researchers devise better treatments for acute tooth pain, such as cavities or infections, and more-chronic conditions, DaSilva says. One such condition is phantom pain that persists in the mouth after a tooth has been removed.

Image: assbach/flickr

Obama Lays Out New Vision for Asteroid, Mars Trips

Posted: 16 Apr 2010 01:45 PM PDT


Speaking at NASA's Kennedy Space Center April 15, President Obama outlined a new plan for the space agency that would forgo sending astronauts back to the moon, but would send humans to an asteroid in 2025 and into orbit around Mars a decade later.


The strategy would rely on private aerospace companies to ferry crew and supplies into space. It would also cancel a program known as Constellation, which is aimed at developing a heavy-lift rocket and vehicles to carry astronauts back to the moon, in favor of pursuing a new rocket that would take humans beyond well beyond that destination.

"I am very happy about the introduction of new innovative commercial approaches in human space flight, because we've been trapped into a very bad cul-de-sac for 40 years," says planetary scientist and former NASA associate administrator for science Alan Stern of the Southwest Research Institute in Boulder, Colo. Stern predicts that Congress is likely to approve Obama's plan.

In Obama's blueprint, NASA would get an additional $6 billion over the next five years to begin developing new space technologies, refocusing its efforts away from designing space transportation vehicles. The plan would, however, keep plans to develop the Orion crew vehicle, which would be the only U.S. space transport vehicle once the shuttle is retired later this year. And in 2015, the agency would evaluate plans for a rocket that would carry astronauts into deep space.

Early next decade, Obama said, "a set of crewed flights will test and prove the systems required for exploration beyond low Earth orbit," culminating in the first human journey to an asteroid in 2025.

Journeys to Mars orbit in the mid-2030s would be followed by a landing on Mars, "and I expect to be around to see it," the president told the cheering crowd.

Obama said he recognized that some experts have called it unwise to rely on the private sector for ferrying crews and supplies into space, but "by buying the services of space transportation rather than the vehicles themselves, we can continue to ensure rigorous safety standards are met but will also accelerate the pace for innovations as companies, from young start-ups to established leaders, compete, design, build and launch new ways of carrying people and materials into space."

Norm Augustine, who chaired a committee that last year criticized the Constellation program and NASA funding, spoke after Obama. The former chairman and chief executive officer of the Lockheed Martin Corp. said the agency "was trapped in low Earth orbit" hauling cargo instead of trying to reach a loftier destination in space. He added that if the agency didn't rely on U.S. companies to take astronauts into space, it would have no alternative but to rely on Russians.

Obama criticized the Bush administration's program to send astronauts back to the moon and then eventually on to Mars as a blueprint that lacked both funding and specific goals. "There are also those who have criticized our decision to end parts of Constellation as one that will hinder space exploration beyond low Earth orbit," Obama said."But by investing in groundbreaking research and innovative companies, we have the potential to rapidly transform our capabilities."

Space-policy analyst Howard McCurdy of American University in Washington, D.C., says he doesn't see much difference in adherence to timetables and goals between Bush's plan and that of Obama's. But he says he's intrigued by Obama's willingness to "leapfrog" over smaller goals. According to McCurdy's interpretation, Obama is telling the public "if we go the moon and concentrate on completing project Constellation, it's going to be a dead end, but if we set our sights a little further out and skip those intermediate steps, we can have real accomplishments."

It's a high-risk proposition, says McCurdy, "but as long as NASA has a monopoly on space transportation, it's going to be like the airline industry in the 1960s — high quality and very expensive.

"The real key in all of this is the ability of the private sector to do what NASA has been unable to do for about the last 30 years, and that is cut the cost to low Earth orbit. As long as NASA was spending $4 billion to $5 billion a year flying the space shuttle, [the agency] was going nowhere," McCurdy says.

Image: NASA

Photos Surface of the Day Einstein Died

Posted: 16 Apr 2010 01:16 PM PDT


Ralph Morse, an ambitious photojournalist for Life magazine, covered a funeral in New Jersey on April 18, 1955. Now, 55 years later, is finally publishing the pictures he took that day, during the funeral and cremation of Albert Einstein.

Einstein had died of heart failure at age 76 earlier that morning at Princeton Hospital. The hospital's pathologist removed his brain for preservation and study, in the hopes that scientists could figure out how he got so smart.

Post-autopsy the body was moved briefly to a funeral home, then to a crematorium in Trenton, New Jersey, for a short service and cremation. (His ashes were scattered later on the grounds of Princeton's Institute for Advanced Study.)

Morse followed the mourners as they returned to Einstein's house at 112 Mercer Street in Princeton. He was the only photographer on the scene during these moving moments.

But when he returned to the Life offices, Morse learned that the magazine wasn't going to publish the pictures. At the request of Einstein's son, Hans Albert Einstein, Life respected the family's privacy while they mourned. Morse and the magazine both forgot about the pictures until recently.

Photo: Einstein's body is moved from the hospital to a funeral home in Princeton.
Ralph Morse/TIME & LIFE Pictures

Oldest Martian Meteorite Not as Old as Thought

Posted: 15 Apr 2010 02:47 PM PDT


The Allan Hills meteorite, named for the site where it was found in Antarctica, was once thought to contain fossil traces of life. That idea has been mostly dismissed, and now the rock also appears to be not quite as old as previously thought.


The oldest known Martian meteorite isn't so old after all. Though it's still the oldest chunk of Mars scientists have ever found, new research suggests the Allan Hills meteorite — officially known as ALH84001 — is about 400 million years younger than previously estimated.

A new analysis published in the April 15 Science pegs the meteorite's age at a mere 4.091 billion years. Previously the meteorite was commonly accepted to have formed 4.51 billion years ago, when the planet's surface was still solidifying out of its primordial magma ocean. But the new age indicates the rock would have formed during a later, chaotic period when Mars was being pummeled by meteorites that fractured and shocked the planet's solid surface.

The Allan Hills meteorite has been a lightning rod for controversy since scientists announced in 1996 that it might hold fossils of Martian bacteria. The scientific community has since mostly abandoned that idea, as one by one every line of evidence for life has been given a non-biological explanation.

"People usually ask me about the life aspect, and I'm so sick to death of that," says Allan Treiman of the Lunar and Planetary Institute in Houston, who was not involved in the new work. Treiman and others now believe that what once looked like fossils is actually rock that was shaped by ordinary geological activity.

The previously accepted age of 4.51 billion years old was calculated in 1995 by measuring radioactive isotopes of samarium and neodymium. Radioactive elements decay from a "parent" isotope (in this case, samarium) to a "daughter" isotope (neodymium) at a set rate. By comparing the amount of the parent element to the daughter element, scientists can infer how long a rock has been around.

"To understand how the Martian mantle has evolved, it's critical to get samples that are old, to see what the mantle sources were early in the planet's history," says Thomas Lapen of the University of Houston, a coauthor of the new study. "This is the only sample in that age range."

Lapen and his colleagues used radioactive isotope dating to calculate the age of the meteorite, using different elements than the 1995 analysis did. Lapen says that the elements used back then were mostly found in minerals called phosphates, which succumb relatively quickly to weathering and geological processes. Like hair dye or a fake ID, weathering could disguise the rock's age in some ways, but not so thoroughly that more reliable indicators are obscured.

"If it's subject to weathering, the phosphate would be the first to be disturbed," Lapen says. "Then ages dependent on the phosphates are altered."

Instead of elements found in phosphates, Lapen's group used lutetium and hafnium, elements that are mostly found in more change-resistant components of the rock. This method showed that the meteorite is just 4.091 billion years old.

Surprisingly, the researchers also found that several younger meteorites have essentially the same composition as the Allan Hills meteorite, meaning some of the same basic geologic processes have been at work on Mars for almost its entire history.

"That connection is perhaps the most amazing outcome of this research," Lapen says. "Mars is a very steady state planet. Igneous processes were happening the same way four billion years ago as they are happening right now."

The new age places the rock's birth date right at a period in the solar system's history when all of the inner planets were being bombarded with meteorites. That could clear up some confusion about the meteorite, Treiman says. Parts of the rock show signs of having been melted and reformed a second time since its birth, which would have been tough to explain if the rock were all original Martian crust.

"That had been a bit of a problem," Treiman says. "You'd have to do whatever mantle processing, whatever happened on the planet, before this rock came to be formed. There's not a lot of time for that."

Image: NASA.

See Also:

Networked Networks Are Prone to Epic Failure

Posted: 15 Apr 2010 11:16 AM PDT


Networks that are resilient on their own become fragile and prone to catastrophic failure when connected, suggests a new study with troubling implications for tightly linked modern infrastructures.

Electrical grids, water supplies, computer networks, roads, hospitals, financial systems –all are tied to each other in ways that could make them vulnerable.

"When networks are interdependent, you might think they're more stable. It might seem like we're building in redundancy. But it can do the opposite," said Eugene Stanley, a Boston University physicist and co-author of the study, published April 14 in Nature.

Most theoretical research on network properties has focused on single networks in isolation. In reality, many important networks are tied to each other. Anecdotal evidence — the crash of communications networks (.pdf) in lower Manhattan after 9/11, the plummeting of markets around the world after the Black Monday stock market collapse of 1987 — hints at their fragility, but the underlying mathematics are largely unexplored.

The Nature researchers modeled the behavior of two networks, each possessing what's known as "broad degree distribution": A few nodes have many connections, some have an intermediate amount of links and many have just a few. Think of the networks as having only a few branches, but many leaves. On their own, such networks are known to be stable. A random failure is likely to disable a leaf, leaving the rest of the network's connections mostly intact.

In the new study, the researchers connected two of these networks. While many node failures were required to crash the networks when they were independent, a few failures crashed the networks when they were linked.

"Networks with broad distributions are robust against random attacks. But we found that broad interconnected networks are very fragile," said study co-author Gerald Paul, a Boston University physicist.

The interconnections fueled a cascading effect, with the failures coursing back and forth. A damaged node in the first network would pull down nodes in the second, which crashed nodes in the first, which brought down more in the second, and so on. And when they looked at data from a 2003 Italian power blackout, in which the electrical grid was linked to the computer network that controlled it, the patterns matched their models' math.

That broad networks could be so fragile is surprising, but even more important is how rapidly the crash happened, with sudden catastrophic collapse instead of a gradual breakdown, said Indiana University informaticist Alessandro Vespignani in a commentary accompanying the paper. "This makes complete system breakdown even more difficult to control or anticipate than in an isolated network," he wrote.

According to Raissa D'Souza, a University of California, Davis mathematician who studies interdependent networks, the findings are "a starting point for thinking about the implications of interactions."

D'Souza hopes such research will pull together mathematicians and engineers. "We now have some analytic tools in place to study interacting networks, but need to refine the models with information on real systems," she said.

Research into linked systems could help engineers build more resilient networks, or identify existing weaknesses. At the very least, they stress the importance of preparing for sudden, catastrophic failures. "We must recognize the possibility of big disasters, and take steps to prepare," said Stanley, noting how unprepared political and economic leaders were for the financial collapse that triggered the current recession.

"These stories underscore that when trouble happens, we're surprised. But we shouldn't be," said Stanley.

Image: From left to wright, a failure cascades through an Italian power network (overlaid on the map) and the internet nodes that depend on it (above the map)./Nature.

See Also:

Citations: "Catastrophic cascade of failures in interdependent networks." By Sergey V. Buldyrev, Roni Parshani, Gerald Paul, H. Eugene Stanley & Shlomo Havlin. Science, Vol. 328 No. 5976, April 15, 2010.

"The fragility of interdependency." By Alessandro Vespignani. Science, Vol. 328 No. 5976, April 15, 2010.

Brandon Keim's Twitter stream and reportorial outtakes; Wired Science on Twitter. Brandon is currently working on a book about ecological tipping points.

Icelandic Volcano’s Ash Plume as Seen From Space

Posted: 15 Apr 2010 10:40 AM PDT


A NASA satellite captured an image of the ash plume from the Eyjafjallajokull volcano's Wednesday eruption. We can see the ash plume from the event sweeping east just north of the United Kingdom en route to Norway.

The plume has disrupted air travel in western Europe, The New York Times reports, because of (well-founded) fears that the silicates in the ash could turn into molten glass inside planes' jet engines.

"The shutdown, among the most sweeping ever ordered in peacetime, forced the cancellation of thousands of flights and left airplanes stranded on the tarmac at some of the world's busiest airports as the rolling cloud — made up of minute particles of silicate that can severely damage airplane engines — spread over Britain and toward continental Europe," the Times reported.

NASA's TERRA imager has had its eye on the Icelandic volcano since it erupted to life March 20 after more than 190 quiet years.


A closeup of the volcano taken on March 24.

See Also:

WiSci 2.0: Alexis Madrigal's Twitter, Tumblr, and green tech history research site; Wired Science on Twitter and Facebook.

Why NASA Is Sending a Robot to Space That Looks Like You

Posted: 15 Apr 2010 10:13 AM PDT


A humanoid robot will visit space for the first time in September aboard the Space Shuttle Discovery, NASA announced Wednesday.

The Robonaut 2, which was co-developed by NASA with General Motors, will serve as an assistant to the humans on board the International Space Station, using the same tools developed for astronauts.

While plain old robots, such as the Mars Phoenix Lander, are a major part of NASA's operations, humanoid robots are a different story. There is significant science-fiction appeal to the idea of humanoid robotic helpers for humans, but does the idea makes more than literary sense? Yes, said Jeffrey Hoffman, an MIT aerospace professor and former astronaut.

"I'm a very strong believer in human-robotic interaction. You can build up a synergy to accomplish what neither humans nor robots could accomplish on their own," Hoffman said. "That's the inspiration behind Robonaut."

Many successful robots, like Kiva's product-distribution robots or the military's little helpers look nothing like humans. And some space researchers like MIT historian and policy analyst David Mindell don't think humanoid robots are a very good idea. But the International Space Station may be the perfect place for a humanoid robot.

"It's incredibly important that Robonaut have a humanoid form factor because he's being sent into space, and it's incredibly expensive, and he has to do a lot to pay himself off," said former roboticist Daniel Wilson (author of How to Build a Robot Army). "It has to be able to pick up any tool that an astronaut could use and go outside."

Wilson argued that space was a uniquely good environment to showcase both the versatility of people and a general-purpose humanoid robot.

"You can't bring a tool to solve every single problem. There's no way. Astronauts can't haul all that shit up there. It's like, 'I have a screwdriver and my brain, and I need to solve the problem, and I don't know what the problem is before I leave the planet,'" Wilson said. "You can use the humanoid to leverage all those tools."

James Hughes, who studies emerging technologies at Trinity University, suggested that humanoid robots may provide a nice middle ground between hardcore human spaceflight evangelists and those who would rather see robotic missions. Most space watchers feel that the human programs are what drives interest and funding in exploration, while scientific investigation will be driven by robots.

"A humanoid robot splits the difference. You get some of the advantages of both and hopefully it will be a nice compromise between the two," said Hughes. "But it may not satisfy either side."

The Robonaut project began in 1996 and the first version of the bot came out in 2000. In 2006, NASA's Dexterous Robotics Laboratory at Johnson Space Center teamed up with GM to design the new robot.

"It is very safe to say that the United States and NASA possess the state of the art in robotic dexterity," said Nic Radford, the Robonaut deputy project manager. "The ideas are limitless."

The bot will be phased into operation in three stages. First, it'll operate only from a fixed position inside the International Space Station. Then, it'll be allowed to move about inside, and finally within a few years, it will be allowed to do extravehicular activities.

"It's really going more to an autonomous system," Radford said. "Right now, it has a task-based system built up of behaviors. We program in a task and based on the sensory input that it receives, it's able to make decisions on what it's going to do next."

The opportunity to test on the robot in orbit has Radford, Wilson and Hoffman excited.

"This has been a dream of our group for a long time," Radford said.

See Also:

WiSci 2.0: Alexis Madrigal's Twitter, Tumblr, and green tech history research site; Wired Science on Twitter and Facebook.

T. Rex of Leeches Found in Amazon Swimmers’ Noses

Posted: 14 Apr 2010 05:30 PM PDT


A toothy leech found in the noses of Peruvian swimmers has called attention to an unrecognized and gruesome branch on the tree of life.

Dubbed Tyrannobdella rex, "tyrant leech king," the pinkie-finger-sized bloodsucker has a single jaw, with teeth five times longer than those found in any other leech.

Described in a paper published April 14 in PLoS ONE, the first specimen was found by doctors in 1997 in the nose of a 6-year-old boy in San Martin, Peru. He had complained of headaches.


Another specimen was taken that year from a 16-month-old boy in Ayacucho, Peru. A decade later, a third T. rex was taken from the nose of a 9-year-old Peruvian girl who felt a "sliding" sensation in her nose. All had bathed frequently in Amazonian streams.

The habit of invading an orifice and feeding on mucous membranes is known as hirudiniasis, and had been seen in a variety of leech species in the Middle East, Africa and Asia. Scientists assumed these species to be unrelated, regarding their feeding habits "only as a loathsome oddity and not a unifying character for a group of related organisms," wrote the researchers.

But when they took a closer look at these species, the researchers noticed anatomical similarities. Genetic comparisons supported the observation. T. rex and the other mucous-membrane feeders actually belong to a single group. DNA differences between them, combined with known mutation rates, suggest a last common ancestor about 200 million years ago, when dinosaurs rose to Earthly dominance.

An ancestor of T. rex may have swum up the other T. rex's nose.

Images: From PLoS ONE: 1. Close-up of the T. rex jaw at left, and its front sucker at right.
2. Examples of other mucous-membrane–feeding leech species.

See Also:

Citation: "Tyrannobdellarex N. Gen. N. Sp. and the Evolutionary Origins of Mucosal Leech Infestations." By Anna J. Phillips, Renzo Arauco-Brown, Alejandro Oceguera-Figueroa, Gloria P. Gomez, Maria Beltran, Yi-Te Lai, Mark E. Siddall.

Brandon Keim's Twitter stream and reportorial outtakes; Wired Science on Twitter. Brandon is currently working on a book about ecological tipping points.

Cassini Captures First Video of Extraterrestrial Lightning

Posted: 14 Apr 2010 11:45 AM PDT

The Cassini spacecraft has captured lightning flashing in a cloud on Saturn's dark side in a first-of-its-kind video.

Scientists have picked up radio signals for years that indicated that lightning storms happened on the planet, but this is the first time that they were able to see and "hear" the electrical storms at the same time.

"This is the first time we have the visible lightning flash together with the radio data," said Georg Fischer, a radio and plasma wave scientist based at the Space Research Institute in Graz, Austria, in a press release. "Now that the radio and visible light data line up, we know for sure we are seeing powerful lightning storms."

The video was shot over 16 minutes and compressed down into the 10 seconds that you see here. The cloud, which is about 1,900 miles along its longest side, is illuminated by the reflection of Saturn's rings. Each flash is about 190 miles (300 kilometers) across with an energy comparable to the most intense lightning here on Earth. In real time, they lasted for about one second.

The crackling soundtrack to the video is synthetic. It approximates the actual sounds received by Cassini's radio recording instrument, which are above the human hearing range.


Images: NASA/JPL/SSI/University of Iowa

WiSci 2.0: Alexis Madrigal's Twitter, Tumblr, and green tech history research site; Wired Science on Twitter and Facebook.

3-Parent Embryos Could Prevent Disease, But Raise Ethical Issues

Posted: 14 Apr 2010 10:54 AM PDT


Researchers have produced human embryos containing DNA from three people, a biotechnological proof-of-principle with profound medical and ethical implications.

To accomplish this, chromosomes were taken from one zygote — the single cell formed when sperm and egg fuse — and put into a zygote stripped of its original chromosomes, but left with its original mitochondria, which provide each human cell with energy.

As they grew, the resulting embryos contained so-called nuclear DNA — the 25,000 genes responsible for physical and developmental traits — from two traditional parents, and mitochondrial DNA from a third.

The technique is a subtle form of genetic engineering, which many people consider taboo, and raises other ethical dilemmas. It could also allow parents whose progeny would otherwise suffer from deadly mitochondrial diseases to have healthy children. It's been done in mice and monkeys, but not in people.

"Previous work showed that these manipulations were possible. This showed that we can get the development of these embryos up to the blastocyst stage," said Doug Turnbull, a Newcastle University neurologist and co-author of the study, published April 14 in Nature.

Thousands of mitochondria float freely in each human cell, using 17 genes to convert oxygen and nutrients into chemical energy. During reproduction, mitochondria in sperm are destroyed. Only the mitochondria in a mother's egg are passed on.

Malfunctions in aging mitochondria have been linked to a variety of common diseases, including Alzheimer's and cancer, but researchers like Turnbull focus on a subset of rare conditions caused early in life by defective mitochondria. About one in 4,000 children develops a mitochondrial disease by age 10. Such diseases are often debilitating, sometimes fatal and presently incurable.

In recent decades, doctors wondered whether defective mitochondria might be swapped for healthy ones in an embryo. In the last few years, sophisticated reproductive technologies and cell-manipulating tools have made that possible — first with mice, and then with more complex creatures.

Two years ago, Turnbull performed the basic steps of the technique with embryos left over from in vitro fertilization. Last August, other researchers performed a variation of the technique, starting with unfertilized eggs rather than zygotes, on rhesus macaque monkeys.

Of 80 embryos in the the Nature study, again taken from IVF leftovers, eight were sustained for six days, long enough to become blastocysts with about 100 cells.

The technique "introduces some inefficiencies because it's more complicated" to use a zygote, said Shoukhrat Mitalipov, an Oregon Health & Science University reproductive biologist who led the rhesus macaque experiment. Both techniques may ultimately be used, depending on circumstance, he said. But the new results are still powerful.

"This is great. We've been thinking about this for years," said Eric Schon, a Columbia University mitochhondrial geneticist. "That possibility is now closer."

Many steps remain before mitochondria swapping could be considered for humans. Though engineered mice have matured and reproduced normally, the monkeys are just a year old. But while safety is yet to be determined, ethical questions are emerging.

One issue involves the nature of parenthood: Would a mitochondrial donor be a parent? Turnbull compared mitochondria to the power source for a laptop. "All the characteristics of the computer are stored on the computer. We're just changing the battery," he said.

Potentially more tricky is the healthy mitochondria's source. While leftover embryos used in Turnbull's approach are plentiful, eggs used by Mitalipov's technique would need to be donated. Egg donation involves a series of grueling and potentially risky hormone treatments.

Marcy Darnovsky, executive director of the Center for Genetics and Society, worried that the risks of mitochondrial swapping might not be immediately evident. She mentioned intracytoplasmic sperm injection, in which sperm is injected directly into an egg. It's an approved workaround for male fertility, but some studies now suggest an increased risk of birth defects (pdf). "Observers have said that human beings were the guinea pigs," Darnovsky said.

Because mitochondria are inherited, both Turnbull's and Mitalipov's techniques are a type of germline, or heritable, genetic engineering. Many people think altering DNA is fine when changes aren't inherited, as with gene therapy to repair eyes, but troubling when traits are passed on. Fearful of designer babies and long-term health uncertainties, countries like France and Germany have banned germline genetic engineering.

Mitochondrial swapping might seem less controversial than regular genetic engineering, because it involves metabolism rather than obvious physical traits. "On the other hand, when embryo manipulations for heritable changes start being done, even with the best intentions, we're on slippery ground," said Darnovsky.

"I think this strategy for handling mitochondrial disease is fascinating, important and ethical, but it certainly crosses the line of engineering genes," said Art Caplan, director of the University of Pennsylvania's Center for Bioethics. "It's a quiet intrusion, but it crosses a line that a lot of people said shouldn't be crossed."

Doug Wallace, a mitochondrial geneticist at the University of California, Irvine, framed the ethics differently. "Is it fair for society to make it impossible for a woman who has a high percentage of mutant mitochondrial issues to have a healthy baby? That's what I'm confronted with in my clinic," he said. "There's an ethic of what's best for the patient."

"For these families, there isn't a cure," said Turnbull. "That's our motivation."

Image: A nucleus is transferred into a recipient zygote./Nature.

See Also:

Citation: "Pronuclear transfer in human embryos to prevent transmission of mitochondrial DNA disease." By Lyndsey Craven, Helen A. Tuppen, Gareth D. Greggains, Stephen J. Harbottle, Julie L. Murphy, Lynsey M. Cree, Alison P. Murdoch, Patrick F. Chinnery, Robert W. Taylor, Robert N. Lightowlers, Mary Herbert, & Douglass M. Turnbull. Nature, Vol. 464 No. 7291, April 15, 2010.

Brandon Keim's Twitter stream and reportorial outtakes; Wired Science on Twitter. Brandon is currently working on a book about ecological tipping points.