News this Week

Science  02 Oct 2009:
Vol. 326, Issue 5949, pp. 26
  1. HIV/AIDS Research

    Surprising AIDS Vaccine Success Praised and Pondered

    1. Jon Cohen
    Unexpected boost.

    Positive results from a massive AIDS vaccine trial in Thailand stunned the beleaguered field.



    That was the reaction of many HIV/AIDS researchers last week to the news that a large clinical trial of an AIDS vaccine worked—the first success in 2 decades of effort. The two vaccines used in the study as a one-two punch had only a modest ability to protect people from HIV, and the results just barely qualified as statistically significant. Researchers will be trying to make sense of the somewhat baffling data for months if not years. But given all the failures in the field, many say that even this relatively weak signal is cause to celebrate.

    The controversial $105 million trial, the largest and most expensive AIDS vaccine study ever conducted, took 6 years and involved more than 16,000 volunteers at eight sites in Thailand. An equal number of people at average risk of becoming infected with HIV were randomly assigned to receive either the vaccine combo, tailor-made to protect against strains circulating in Thailand, or a saline placebo. Participants were mainly heterosexual, and about one-fourth reported high-risk behavior such as commercial sex work or intravenous drug use.

    The trial was widely expected to fail because neither of the vaccines had done well by themselves in clinical studies. Indeed, such lackluster results with one of the vaccines, a canarypox virus that has three HIV genes stitched into it, led the U.S. National Institute of Allergy and Infectious Diseases (NIAID) to pull the plug in 2002 on a large trial that mirrored the Thai study (Science, 1 March 2002, p. 1616). And the second vaccine, a recombinant form of the HIV surface protein gp120, later outright failed in two large-scale efficacy trials (Science, 21 November 2003, p. 1309). As a result, many investigators were dumbfounded to learn that at the end of the Thai study in June, 51 vaccinated people had become infected within 3 years of receiving their last shot, as compared with 74 people in the placebo group. The p value, which indicates whether results are due to chance, was less than 0.039, just below the widely accepted “significance” cutoff of 0.05. No serious adverse events were seen in either group.

    Trial results were announced on 24 September in media briefings held by the U.S. Army, the main sponsor of the trial, and the Thai Ministry of Public Health. “Although the level of protection was modest, we think the study is a major scientific advance,” said Colonel Jerome Kim, HIV vaccines product manager for the U.S. Army.

    Even skeptics are careful not to rain on the parade. “Looking at the numbers, it's underwhelming to me,” says Ronald Desrosiers, head of the New England Primate Research Center in Southborough, Massachusetts. “But I want to sit tight and get a bunch of people to do analyses and see whether the protective effect holds up.” Desrosiers was one of 22 researchers who argued in a Science Policy Forum that the study never should have been launched (Science, 16 January 2004, p. 316).

    NIAID Director Anthony Fauci also has reservations. “This is a modest effect, and we have a lot of questions,” says Fauci, whose institute ended up funding about 75% of the study after Congress decided it should oversee the U.S. military's AIDS program. Still, he is excited by the possibility that there's even a trend toward efficacy. “If you look at the results of every other vaccine trial, it's bupkis,” he said. “There isn't even the hint of a signal.”

    Supporters and critics alike agree that analyzing stored blood samples from the vaccinated people may uncover the immune responses that protected them. These so-called correlates of protection have been a Holy Grail to AIDS vaccine researchers, who have relied on different immunologic theories to design vaccines. “The real correlates of protection might be something we haven't been examining up until this point,” says Norman Letvin, an AIDS vaccine researcher at the Beth Israel Deaconess Medical Center in Boston. “If that's the case, it's of enormous importance.”

    It's also possible that an AIDS vaccine may not have to be extremely powerful to work. “These vaccines induce some very weak immune responses, so in a sense this may be very good news because it may suggest that much less potent responses than we expected may have an impact on the acquisition of infection,” says Dennis Burton, an immunologist at the Scripps Research Institute in San Diego, California.

    One of the most perplexing findings is that the vaccines prevented infection by HIV but failed to reduce levels of the virus in people who did become infected. “Most people expected it would be the other way around,” says Colonel Nelson Michael, director of the U.S. Military HIV Research Program.

    That odd result in turn raises questions about the presumed “prime-boost” mechanism of the vaccines. The canarypox vaccine, made by Sanofi Pasteur based in Lyon, France, primarily cranks up the cell-mediated arm of the immune system, which clears cells after they have become infected. The booster shot of gp120, supplied by Global Solutions for Infectious Diseases in South San Francisco, California, was supposed to somehow fortify that cell-mediated response. Even ardent proponents believed that this vaccine combo was more likely to blunt infections than prevent them. “Maybe we were wrong,” says Michael. “We finally have an argument that will be suffused with data rather than theories.”

    No one anticipates that these results will lead countries to license the vaccines, and even the trial's chief statistician acknowledges that a few more infected vaccinees could have tipped the scale toward statistical insignificance. “The results tell us two things: These vaccines work, and they don't work well enough,” says statistician Donald Stablein, president of the Emmes Corp. in Rockville, Maryland.

    Many researchers hope that when the full data are released at an AIDS vaccine conference in Paris from 19 to 22 October, they will help with the design of future vaccines, as the information might lead to refined animal models and improved analyses of small-scale human studies. Skeptics, of course, will also be scouring the results to see whether factors such as risk behavior, circumcision, or the strains of the virus that caused infections might explain the odd results. “It's very early days,” says Burton. “People should be enormously cautious now.”

  2. Space Science

    Mars Mission Delayed as Mad Dash to Prep Probe Falls Short

    1. Richard Stone

    BEIJING–For the Russians, it would have been a bounce back from the disastrous launch of the Mars 96 spacecraft 13 years ago. For the Chinese, it would have been a maiden attempt to explore another planet. The two nations were gearing up to send a pair of probes next month to Mars and Phobos, the larger of the two martian moons, and return samples from Phobos—the first such mission in more than 30 years. But a breakneck effort to get the main spacecraft ready fell short, and last week the Russian Federal Space Agency, known as Roscosmos, announced that the launch will be postponed until 2011—the next favorable window.

    “It's a pity,” says Wu Ji, chief scientist for China's probe—Yinghuo-1—and director of the Center for Space Science and Applied Research here. The delay is unavoidable, adds Lev Zelenyi, director of the Space Research Institute (IKI) in Moscow. “We want to increase the reliability of the mission and test all systems again before final launch,” he says. But there could be a silver lining: Russia may be able to add instruments to the payload, Zelenyi says.

    Mars is a popular destination for planetary missions, with 39 having been launched to date. “Almost all focused on finding signs of life,” says Wu. Russia's Mars 96 probe aimed to do that as well, and much more, but the spacecraft crashed after launch in November 1996, and Russia hasn't attempted a planetary mission since.

    The Sino-Russian mission would offer a fresh approach. After a 10-month journey, the 11-ton Russian Phobos-Grunt spacecraft would enter orbit and sling the bantamweight 110-kilogram Chinese probe, Yinghuo-1, or “firefly,” into a 3-day elliptical orbit around Mars. Yinghuo-1 would take readings of the martian ionosphere and snap photos of the surface during low passes, hoping to catch the genesis of one of Mars's famous planet-sized dust storms. “Yinghuo-1 will be the first comprehensive survey of the martian space environment,” says Wu. “We hope to do something that has never been done before.” Phobos-Grunt, meanwhile, would transmit radio waves to Yinghuo-1 through the ionosphere to glean insights into its structure. After several months of studies in orbit, Phobos-Grunt would land on the martian moon, take soil samples, and head back to Earth.

    Not going anywhere.

    A 2-year delay won't alter the science objectives at Phobos.


    Phobos-Grunt would also ferry the Living Interplanetary Flight Experiment (LIFE): a titanium canister filled with 10 kinds of microbes from the three domains of life, bacteria, eukaryota, and archaea. The setup, provided by The Planetary Society in Pasadena, California, intends to test whether microbes—in this case a collection harmless to humans—can survive for years in space, mimicking conditions in which microbes might theoretically survive inside a meteoroid.

    All that will have to wait. Rumors had been circulating for months that Phobos-Grunt might be postponed, but until last week the mission was a go, and Wu for one was planning to head to Kazakhstan for a late-October launch. His group's disappointment comes hard on the heels of news that China may not find the money to launch another mission, the Hard X-ray Modulation Telescope (Science, 25 September, p. 1613).

    But more time might buy a better mission. In the next 2 years, IKI will undertake additional tests of its soil sampler. The delay should also allow them to restore to the payload a secondary ion spectrometer, a low-speed dust-particle detector, and perhaps an infrared spectrometer, says IKI's Alexander Zakharov, chief scientist for Phobos-Grunt. LIFE, meanwhile, is merely being put on hold. “We anticipate loading new organisms into a flight module in 2011,” says LIFE's experiment manager, Bruce Betts. The Chinese and Russians insist they'll get the same data, just a tad later. After all, notes Zelenyi, “Phobos, as a celestial body, will not change in 2 years.”

  3. Climate Change

    What Happened to Global Warming? Scientists Say Just Wait a Bit

    1. Richard A. Kerr

    The blogosphere has been having a field day with global warming's apparent decade-long stagnation. Negotiators are working toward an international global warming agreement to be signed in Copenhagen in December, yet there hasn't been any warming for a decade. What's the point, bloggers ask?

    Climate researchers are beginning to answer back in their preferred venue, the peer-reviewed literature. The pause in warming is real enough, but it's just temporary, they argue from their analyses. A natural swing in climate to the cool side has been holding greenhouse warming back, and such swings don't last forever. “In the end, global warming will prevail,” says climate scientist Gavin Schmidt of NASA's Goddard Institute for Space Studies (GISS) in New York City.

    The latest response from the climate community comes in State of the Climate in 2008, a special supplement to the current (August) issue of the Bulletin of the American Meteorological Society. Climate researcher Jeff Knight and eight colleagues at the Met Office Hadley Centre in Exeter, U.K., first establish that—at least in one leading temperature record—greenhouse warming has been stopped in its tracks for the past 10 years. In the HadCRUT3 temperature record, the world warmed by 0.07°C±0.07°C from 1999 through 2008, not the 0.20°C expected by the Intergovernmental Panel on Climate Change. Corrected for the natural temperature effects of El Niño and its sister climate event La Niña, the decade's trend is a perfectly flat 0.00°C.

    Steady as she goes.

    The global average temperature (gray line; adjusted in blue) has remained steady the past 10 years, as shown by the orange trend lines.


    So contrarian bloggers are right: There's been no increase in greenhouse warming lately. That result came as no surprise to Knight and his colleagues or, for that matter, to most climate scientists. But the Hadley Centre group took the next step, using climate modeling to try to quantify how unusual a 10-year warming pause might be. In 10 modeling runs of 21st century climate totaling 700 years worth of simulation, long-term warming proceeded about as expected: 2.0°C by the end of the century. But along the way in the 700 years of simulation, about 17 separate 10-year intervals had temperature trends resembling that of the past decade—that is, more or less flat.

    From this result, the group concludes that the model can reproduce natural jostlings of the climate system—perhaps a shift in heat-carrying ocean currents—that can cool the world and hold off greenhouse warming for a decade. But natural climate variability in the model has its limits. Pauses as long as 15 years are rare in the simulations, and “we expect that [real-world] warming will resume in the next few years,” the Hadley Centre group writes. And that resumption could come as a bit of a jolt, says Adam Scaife of the group, as the temperature catches up with the greenhouse gases added during the pause.

    Pinning the pause on natural variability makes sense to most researchers. “That goes without saying,” writes climate researcher Stefan Rahmstorf of Potsdam Institute for Climate Impact Research in Germany by e-mail. “We've made [that point] several times on RealClimate,” a blog. Solar physicist Judith Lean of the Naval Research Laboratory in Washington, D.C., and climate modeler David Rind of GISS reached the same conclusion in a peer-reviewed 15 August paper in Geophysical Research Letters. They broke down recent temperature variation into components attributable to greenhouse gases, pollutant aerosols, volcanic aerosols, El Niño/La Niña, and solar variability. Combined, those influences explain all of the observed variability, by Lean and Rind's accounting. But unlike the Hadley Centre's model-based analysis, this assessment attributes a good deal of climate variability to variability in solar activity. That's because most models can't translate solar variability into climate variability the way the actual climate system can (Science, 28 August, p. 1058), Rind says.

    Researchers may differ about exactly what's behind recent natural climate variability, but they agree that no sort of natural variability can hold off greenhouse warming much longer. “Our prediction is that if past is prologue, the solar component will turn around and lead to rapid warming in the next 5 years,” says Rind. Climate modeler David Smith of the Hadley Centre, who was not involved in the State of the Climate analysis, says his group's climate model forecasts—made much the way weather forecasts are made—are still calling for warming to resume in the next few years as ocean influences reverse (Science, 10 August 2007, p. 746). Whether that's in time to boost climate negotiations is anyone's guess.

  4. Biosecurity

    Lawmakers Signal Tougher Controls on Pathogen Research

    1. Yudhijit Bhattacharjee

    In the 8 years since the 2001 anthrax letter attacks, new biocontainment labs have sprung up around the United States as part of a massive national effort to counter bioterrorism threats. Now, a crescendo of concerns over the security of these labs, voiced by lawmakers and experts at two congressional hearings last week, threatens to slow the booming biodefense industry.

    Both hearings—in the House of Representatives and in the Senate—featured testimony from Nancy Kingsbury of the Government Accountability Office (GAO), whose agency released a report on 21 September that calls for entrusting a single federal entity with determining whether any more biocontainment labs are needed; what standards of design, maintenance, and operation such labs must meet; and how they should be overseen. Those recommendations dovetail with a bill introduced by senators Joe Lieberman (I–CT) and Susan Collins (R–ME) on 9 September, under which the Department of Homeland Security (DHS) would be charged with establishing and enforcing new security standards for biocontainment labs. Currently, labs where researchers work with select agents—a subset of the broader universe of dangerous pathogens and toxins—are overseen by the select agent program, administered by the Department of Health and Human Services (HHS) and the U.S. Department of Agriculture (USDA).

    GAO does not think the current system is adequate. “The number of BSL [biosafety level]-3 and BSL-4 labs has been proliferating at a considerable rate since the anthrax attacks because the government has been throwing money at this kind of research, but there's nobody in charge,” Kingsbury told Science. She says the number of labs registered under the select agent program has more than tripled since 2004, to 1362 as of 2008.

    Over capacity.

    GAO's Kingsbury asks whether the United States already has too many biocontainment labs.


    “We need to know whether we need more of these labs or whether we already have too many,” Kingsbury said. She was especially concerned that an increase in the number of researchers working with hazardous pathogens would “inevitably” lead to an amplified risk of a bioterrorist attack perpetrated by a scientist working at a biocontainment facility. (In August 2008, the Federal Bureau of Investigation implicated U.S. Army researcher Bruce Ivins in the 2001 anthrax attacks [Science, 8 August 2008, p. 754].)

    At the Senate hearing, lawmakers and officials from the Department of Defense and DHS spoke favorably of a tiered system for pathogens in which facilities and researchers dealing with the most dangerous microorganisms would be subject to the most stringent controls. The bill introduced by Lieberman and Collins calls for exactly such a classification. Under it, over a dozen pathogens, including anthrax, smallpox, and ebola, would be governed by tougher security standards than are required by the select agent rules. Rules for a second tier of select agents would be more lenient than they are now. Labs working with a third tier of pathogens would have to register with the government to help coordinate a rapid response in case of an outbreak.

    Many in the biodefense research community oppose more regulations or a change from the status quo. Ronald Atlas of the University of Louisville in Kentucky, who testified before the House panel on behalf of the American Society for Microbiology (ASM), says he supports the idea of tiering but wants HHS and USDA to remain in charge. “There is concern that the expertise at DHS is not sufficient in the life sciences,” Atlas says. Gerald Epstein of the Center for Strategic and International Studies in Washington, D.C., says that DHS's system of ensuring the reliability of its own employees is so “dysfunctional and byzantine” that “it does not have any business” screening researchers working at other biocontainment labs.

    As to how many labs are enough, Atlas says: “There would be value in having federal coordination with regard to the federal investment in such labs. But that sort of oversight should not interfere with the ability of private and academic institutions to construct containment labs using other sources of funding as long as those labs meet biosafety standards.”

    ASM is urging Congress to hold off on passing any biosecurity legislation until an interagency task force on securing labs and countering the insider threat releases its recommendations later in the fall. Meanwhile, the biodefense enterprise is continuing to grow. In August, the U.S. Army Medical Research Institute of Infectious Diseases broke ground in Frederick, Maryland, for a new facility that will expand the institute's BSL-3 and BSL-4 lab space. At the same time, a National Research Council panel is studying whether safety and security practices at USAMRIID—from where the anthrax attacks were purportedly launched—are adequate.

  5. ScienceInsider

    From the Science Policy Blog

    The U.S. Food and Drug Administration has admitted that “unprecedented” pressure from New Jersey politicians led it to approve a medical device that its scientists said was flawed.

    Roger Beachy has been chosen to head the National Institute of Food and Agriculture, which replaces the Cooperative State Research, Education, and Extension Service at the U.S. Department of Agriculture. Beachy is director of the Donald Danforth Plant Science Center in St. Louis, Missouri. Arun Majumdar has been nominated to run the new Advanced Research Projects Agency–Energy at the Department of Energy (DOE). The materials scientist comes from Lawrence Berkeley National Laboratory, and his new boss at DOE is his old boss at the lab—Energy Secretary Steven Chu.

    A new online journal, Nature Communications, will allow authors to pay a fee so that their paper will be freely available online the moment it's published. The journal will cover all disciplines and debuts this month.

    A lavishly equipped graduate university with a multibillion-dollar endowment from the king officially opened last week along the shores of the Red Sea in Saudi Arabia. King Abdullah University of Science and Technology touted its Western-style approach to graduate education and research in a gala inauguration.

    A case of fabricated data has caused upheavals at Switzerland's top university, ETH Zürich. An internal investigation exonerated its vice president for research, in whose lab the fabrication occurred, but he nevertheless resigned his post. The investigation pointed to a former graduate student who is now suing ETH Zürich to block publication of the report.

    Last week's 1-day U.N. General Assembly summit on climate change gave Chinese President Hu Jintao a chance to tell the world that China stands ready to negotiate.

    For more science policy news, visit

  6. Forensic Science

    Scientists Decry Isotope, DNA Testing of ‘Nationality’

    1. John Travis
    The jungle.

    Many refugees in this French camp—now disbanded—sought asylum in Europe, particularly in the United Kingdom.


    CAMBRIDGE, UNITED KINGDOM—Scientists are greeting with dismay a project to use DNA and isotope analysis of tissue from asylum-seekers to evaluate their nationality and help decide who can enter the United Kingdom. “Horrifying,” “naïve,” and “flawed” are among the adjectives geneticists and isotope specialists Science contacted used to describe the “Human Provenance pilot project,” launched quietly in mid-September by the U.K. Border Agency. Their consensus: The project is not scientifically valid—or even sensible.

    “My first reaction is this is wildly premature, even ignoring the moral and ethical aspects,” says Alec Jeffreys of the University of Leicester, who pioneered human DNA fingerprinting.

    U.K. immigration policies have been under scrutiny recently as the number of people claiming asylum has soared and as French police in Calais last week cleared a camp of migrants hoping to make it across the English Channel. The existence of a DNA-based program to identify nationality was revealed in late September by the Daily Mail and The Observer, sparking protests from refugee advocates. Science has obtained Border Agency documents showing that isotope analyses of hair and nail samples will also be conducted “to help identify a person's true country of origin.” The project “is regrettable,” says Caroline Slocock, chief executive of Refugee and Migrant Justice headquartered in London. Although asylum-seekers are asked to provide tissue samples voluntarily, turning down a government request for tissue could be misinterpreted, she says, “so we believe [the program] should not be introduced at all.”

    The Border Agency's DNA-testing plans would use mouth swabs for mitochondrial DNA and Y chromosome testing, as well as analyses of subtle genetic variations called single-nucleotide polymorphisms (SNPs). One goal of the project is to determine whether asylum-seekers claiming to be from Somalia and fleeing persecution are actually from another African country such as Kenya. If successful, the Border Agency suggests its pilot project could be extended to confirming other nationalities. Yet scientists say the Border Agency's goals confuse ancestry or ethnicity with nationality. David Balding, a population geneticist at Imperial College London, notes that “genes don't respect national borders, as many legitimate citizens are migrants or direct descendants of migrants, and many national borders split ethnic groups.”

    After reviewing the Border Agency's plans, Jeffreys echoed those criticisms in an e-mail to Science: “The Borders Agency is clearly making huge and unwarranted assumptions about population structure in Africa; the extensive research needed to determine population structure and the ability or otherwise of DNA to pinpoint ethnic origin in this region simply has not been done. Even if it did work (which I doubt), assigning a person to a population does not establish nationality - people move! The whole proposal is naive and scientifically flawed.”

    Another geneticist says the Forensic Science Service, a former government agency that has been privatized, requested his opinion earlier this year on how to develop a genetic assay to distinguish among East African populations. “I thought it was for forensic purposes, not border control,” says Christopher Phillips of the University of Santiago de Compostela in Spain, who with colleagues recently used a DNA sample to correctly infer the ancestry of a suspect in the 2004 train bombings in Madrid.

    Mark Thomas, a geneticist of University College London who considers the Human Provenance program “horrifying,” contends that even determining a person's ancestry—as distinct from nationality—is more problematic than many believe. “mtDNA will never have the resolution to specify a country of origin. Many DNA ancestry testing companies have sprung up over the last 10 years, often based on mtDNA, but what they are selling is little better than genetic astrology,” he says. “Dense genomic SNP data does have some resolution … but not at a very local scale, and with considerable errors.”

    Details of the plan to use isotope analyses in addition to DNA analyses have intensified skepticism. The plan is to look for ratios of certain isotopes in tissue that could be matched to ratios in the environment where a person was born or grew up. But isotope specialists point to a seemingly obvious flaw: There's no scientifically accepted evidence that isotope signatures at birth or during childhood are still present in adult samples of constantly growing tissues such as hair and nails. At best, researchers say, those tissues reflect the past year or so of a person's life. “It worries me as a scientist that actual peoples' lives are being influenced based on these methods,” says Jane Evans, head of Science-based Archaeology at the National Environment Research Council Isotope Geosciences Laboratory in Nottingham.

    Although the agency hasn't detailed the isotopes it is examining, the use of hair and nail samples suggests that the tests will look at “lighter” element isotopes, such as those of hydrogen, oxygen, carbon, and nitrogen, all of which are incorporated into the keratin and other proteins as those tissues grow. Isotopes of strontium and other “heavier” elements incorporate into bones and teeth throughout life and some evidence suggests that strontium measurements can match people to geographic locales in which they were born, or at least grew up. In contrast, the lighter isotopes in tissues such as hair and nails being collected by the Border Agency are typically used to reveal recent diets and climatic conditions, not ethnicity. “I don't think I could tell the difference between a Kenyan and a Somalian,” says Tamsin O'Connell of the University of Cambridge in the United Kingdom, an archaeologist who specializes in studying light isotopes from soft tissues.

    O'Connell, Evans, and others say they're puzzled that one Border Agency document titled “Nationality-Swapping” uses the notorious “Adam Torso” case as a proof of principle for employing isotope analysis. In this highly publicized murder in 2001, only the mutilated torso of a teenager was found in the Thames river. Using isotope analysis, “the child's body was traced to a small Nigerian town in an area about 100 × 50 km wide,” a Border Agency document states. (To read the documents describing the program and hear more reaction, follow the story at ScienceInsider.) The document notes, however, that the analysis was done on bones, not on hair and teeth. “It's like adding 2 and 2 and getting 3½,” says Jessica Pearson of the University of Liverpool, who uses isotope signatures from fossils to examine the diet of ancient humans. Pearson also points out that the forensic methods used in the Adam Torso case are impossible to evaluate because they still haven't been described in a scientific publication or discussed in court.

    Having their fate rest on unproven methods is particularly dangerous for asylum-seekers in the United Kingdom, notes Phillips, because, unlike criminal defendants, they have limited or no rights to challenge evidence or appeal. “You can't parachute in a technique if it isn't properly validated,” he says.

    The Border Agency says only asylum-seekers who have already failed linguistic tests—another contested method of determining nationality—will be asked to provide mouth swabs, hair and nail samples. It also released a written response to scientific criticisms, which said: “Ancestral DNA testing will not be used alone but will combine with language analysis, investigative interviewing techniques and other recognized forensic disciplines. The results of the combination of these procedures may indicate a person's possible origin and enable the UKBA to make further enquiries leading to the return of those intending on abusing the U.K.'s asylum system. This project is working with a number of leading scientists in this field who have studied differences in the genetic backgrounds of various population groups.”

    The Border Agency has not yet responded to a request to identify the scientists it is working with, nor has it cited any scientific papers that validate its DNA and isotope methods. It's also not clear who is conducting the DNA and isotope analyses for the Border Agency. Evans says her lab, which is arguably the United Kingdom's leading academic center for isotope studies, is not involved. Several researchers say they suspect private labs are doing most of the work—and they question if such labs have been properly vetted for reliability. Among their many concerns, some scientists also worry that statistical uncertainties may be overlooked.

    A Border Agency spokesperson defended its Human Provenance program as a “small pilot at the moment. It's in its baby stages. We want to get feedback.” They're getting plenty of that from outraged scientists. “I'd hate to see asylum decisions made [with these methods]. We're dealing with people's lives,” says Pearson.


    From Science's Online Daily News Site

    The Upside of Recessions You've lost your job, your house, and your savings. But, hey, you still have your health, right? Actually, you probably do—and it may even be improving. Researchers have found that, historically, Americans were healthier during the Great Depression and other economic downturns than they were during periods of prosperity. And they say the trend may still hold true today.

    Dylan to Darwin: Don't Look Back Evolution doesn't make U-turns, according to a new study of proteins. The research shows that simply reversing selective pressure won't make a biomolecule revert to an earlier form. The finding confirms a much-debated biological law that, evolutionarily speaking, there's no going back.

    Wolf in Coyote's Clothing Farmers depend on hybrid vigor for improved crop yields, as seeds produced from different strains of, say, corn, can lead to superior crops. Hybrid vigor seems to have worked for coyotes in the Northeastern United States as well, according to a genetic study and physical analysis of the animals: Coyotes in this part of the United States are bigger than their western counterparts because, as their ancestors migrated into the territory, they mated with wolves along the way.


    Taking the Tally of Curious Triangles What do the numbers 5, 6, 7, 13, 14, 15, 20, 21, 22, and 23 have in common? They're all “congruent” numbers, that is, numbers related to the areas of certain triangles. Even if that answer didn't leap to mind, you may be intrigued to know that mathematicians have now cataloged the congruent numbers—which are easy to define but not so easy to spot—up to a trillion.

    Read the full postings, comments, and more on

  8. Origins

    On the Origin of Ecological Structure

    1. Erik Stokstad

    What dictates the kinds and proportions of organisms in a community? In the 10th essay in Science's series in honor of the Year of Darwin, Erik Stokstad explores the question of the relative importance of the various forces that act on a biological community.


    On 23 June 1802, Prussian naturalist Alexander von Humboldt attempted to reach the summit of Mount Chimborazo, the highest peak in the northern Andes. Bleeding, his beard caked with ice, the 33-year-old Humboldt worked his way along a 12-centimeter-wide ridge only to be blocked by a cliff some 400 meters from the top. Humboldt's barometer indicated 5878 meters—a climbing record unbeaten for decades and one that brought him international fame.

    The lasting impact of the trip, however, came from his explorations of somewhat less lofty terrain. Having studied Mount Chimborazo and nearby peaks for months, Humboldt assembled the first comprehensive treatise—Essay on the Geography of Plants—on how vegetation varies with altitude, climate, soil, and other factors. The work was a groundbreaking exploration of the physical underpinnings of ecological structure: what determines the species that make up a community and their relative abundance.

    More than a half-century later, Charles Darwin quietly conducted experiments in his garden at Down House that were even more seminal. Examining a patch of unkempt lawn as it went to seed, Darwin observed that the species changed through time: “more vigorous plants gradually kill the less vigorous, though fully grown plants,” he wrote; nine of the original 20 species eventually disappeared. It was a compelling demonstration of competition, which became a cornerstone, albeit a controversial one, for community structure, and Darwin included the experiment in On the Origin of Species. “What a wondrous problem it is,” Darwin wrote to the botanist Joseph Hooker in 1857, “what a play of forces, determining the kind and proportion of each plant in a square yard of turf!”

    Ever since, ecologists have wrestled with understanding what dictates the kinds and proportions of organisms in communities ranging from meadows to montane forests. How these forces set up communities has “arguably been one of the most primary questions driving ecological science since its origins,” says Brian Enquist of the University of Arizona, Tucson. Competition, predation, disturbance, and other factors have a heavy hand, and new research is showing the influential role of evolution as well. “You can't understand the assembly process if you don't think about evolution,” says Jeannine Cavender-Bares of the University of Minnesota, Twin Cities.

    Despite these achievements, there is still no consensus on the relative importance of the various forces. Darwin and many later ecologists emphasized competition among species, but proponents of a controversial theory of biodiversity that assumes competition has no impact argue that immigration and other random demographic events can account for much of the apparent makeup of communities. As a result, ecologists have a long way to go to come up with formulas that predict how communities might arise and change. Yet the ability to make predictions is important for the restoration and management of ecosystems impacted by invasive species or climate change.

    Many forces

    Species abundance and composition—i.e., structure—may be the salient feature of a biological community. A tropical rainforest, for example, is physically dominated by tall, broad-leafed trees with several layers of trees underneath adapted to lower light. Woody vines and epiphytes dangle from the branches, and shade-tolerant shrubs dot the forest floor. Even though the particular species vary from place to place, wet tropical forests still exist as recognizable entities on four continents. A combination of physical and biological forces organizes species into these predictable communities.

    Following Humboldt's lead, scientists in the 19th century assembled evidence that the composition of communities depends on physical factors such as climate and soil chemistry. Today, ecologists call these factors “environmental filters” that broadly determine which species can live where. For example, forests in the eastern United States are rich in sugar maples in the north but gradually become dominated by oaks and hickories to the south as temperature rises. Hemlock and beech trees disappear to the west as conditions generally become drier.

    On a global scale, the importance of physical factors varies with latitude, according to conventional thinking, popularized by Theodore Dobzhansky in 1950. Stress from cold and freezing limits diversity at high latitudes, according to this widely established view, whereas species diversity in the tropics is capped by another major driver, biological interactions.

    But to what degree are local patterns driven by the direct influence of climate versus biological interactions such as competition? “Answering this question is critical for our ability to predict shifts in natural communities due to global climate change,” says Nicholas Gotelli of the University of Vermont, Burlington.

    It's long been clear that biological interactions—competition, predation, and so on—can be big players. In the 1930s, Soviet microbiologist Georgii Gause conducted influential research into how competition sets up communities. Gause studied mixtures of three species of the protist Paramecium that were provided with one or two kinds of food: yeast, bacteria, or both. The experiments revealed that one species of Paramecium would always drive the others extinct if they had to compete for the same resource. This led to the principle of competitive exclusion and eventually to the idea that species that are ecologically too similar cannot coexist. Although ecologists now know that the natural world is more complicated—there are ways for similar species to coexist—the principle had a major impact on thinking about the structuring of communities.

    Over subsequent decades, ecologists recognized that predators, too, can strongly shape communities. Working in rocky tide pools of the Pacific Northwest, for example, Robert Paine of the University of Washington, Seattle, proposed in 1966 that species diversity is controlled by keystone predators. By eating species that are strong competitors within the food web, keystone predators help weaker competitors persist. Sea stars, for example, feed on mussels and keep them from crowding out barnacles and algae.

    In the zone.

    Alexander von Humboldt (above, left) compared the influence of elevation on plant communities on Mount Chimborazo (left), Mont Blanc, and Sulitelma.


    A species doesn't have to be a predator or a competitor to have a profound effect. By altering the physical environment, some species influence which organisms live where. When beavers build dams they flood land, providing new aquatic habitat for fish and amphibians. Corals create a three-dimensional space full of places to hide, eat, and live for a wide variety of marine life. Thus one organism can facilitate the settlement or success of another.

    Debating competition

    Although certain ecosystems present clear examples of how biological interactions shape communities, coming up with general principles has been much more difficult. Arguments have raged for decades about the relative importance of factors such as competition, predation, and chance events: colonization, for example. A major debate about competition and how to spot it kicked off in 1975, when Jared Diamond of the University of California, Los Angeles, proposed seven broad patterns of species distributions, which he dubbed “assembly rules,” for communities. The first rule was that only some of all the possible combinations of species actually coexist in nature. Diamond identified several instances of “forbidden species combinations,” based on literature and fieldwork on fruit-eating birds living in the Bismarck Archipelago and Solomon Islands near New Guinea. For example, the black honeyeater (Myzomela pammelaena) lives on 23 of the 41 surveyed islands in the Bismarck Archipelago, but not on any of the 14 islands inhabited by the black sunbird (Nectarinia sericea). Both birds are about the same size and use curved bills to sip nectar, and Diamond noted that competition affects their distribution.

    But without any experimental evidence or strong statistical tests, it was a bold leap to conclude that competition was a major force structuring island communities. Another interpretation came from Daniel Simberloff and Edward Connor, then at Florida State University, Tallahassee. Starting in 1979, they argued that patterns of species distribution on these islands appeared to be random. “The pattern was eye-balled,” Simberloff says of Diamond's results.

    The disagreement continues to this day. Working with James Sanderson of the Wildlife Conservation Network in Los Altos, California, and Stuart Pimm of Duke University in Durham, North Carolina, Diamond published a new analysis of the bird species of the Bismarck and Solomon Islands in Evolutionary Ecology Research in July. By using what they say are more sophisticated statistical tests, the team verified that the patterns of species combinations identified by Diamond in 1975 were indeed highly unlikely to be due to chance. Although chance may determine which species end up colonizing an island, interspecific competition then tends to keep out ecologically similar species, Pimm says. Simberloff, meanwhile, has a paper in press in which he finds that the patterns in the same data are better explained by the historical and chance factors that control how birds disperse than by competition.

    A handful of so-called assembly rules have been proposed since Diamond's early work popularized the search for these patterns. But local communities are so varied that it seems difficult to extrapolate from one to another. “I think what we're going to find out is that assembly rules are vague, gentle constraints,” says Evan Weiher of the University of Wisconsin, Eau Claire.

    In 1997, Stephen Hubbell, now at the University of Georgia, Athens, proposed an alternative to assembly driven by competition or other biological interactions. Instead, Hubbell suggested, the abundance and diversity of species in a community is determined mainly by random dispersal, speciation, and extinction. The idea, which he dubbed the “unified neutral theory of biodiversity,” makes a radical assumption: It considers all organisms of the same trophic level (plants, say, or herbivores) as demographically identical; that is, each organism in a particular level has about the same chance of reproducing, dying, migrating, or giving rise to a new species. Testing the idea on a 50-hectare plot of tropical forest in Panama, Hubbell showed that the model predicted the species richness and relative abundance in the area. Hubbell doesn't dispute that some species differ in their ability to compete, but competition wasn't really an important factor in determining what plants grew where, he noted.

    Neutral theory has generated a lot of interest, especially among theorists, and controversy. On the one hand, researchers find it appealing because of its simplicity and the fact that it provides predictions for many kinds of communities. But many ecologists remain skeptical of the assumption that species are essentially equivalent in how they function in the community. A recent paper by Nathan Kraft of the University of California, Berkeley, and others even challenges the adequacy of neutral theory in tropical forests, where it was first proposed, and instead makes a case for functional differences among species, and perhaps competition, as contributing factors (Science, 24 October 2008, p. 580).

    Researchers also point out that biological interactions and “neutral” factors, such as the stochastic effects of dispersal, aren't mutually exclusive. Both can sometimes happen in different ways simultaneously. For example, in a 2005 paper in Ecology Letters, Tadashi Fukami, now of Stanford University in Palo Alto, California, and Wim Van der Putten of Wageningen University in the Netherlands described a 9-year experiment with plants on abandoned farmland. They found that small communities of plants ended up with the same array of functional traits, such as whether a seed is dispersed by an animal or whether the plant is a perennial, indicating that biological interactions were determining what kinds of plant species could successfully establish. But the particular species that showed up were essentially random selections from the regional species pool, a result consistent with neutral theory.


    Structure results from many sources, including predators such as star fish and habitat-building organisms such as coral; physical factors such as temperature also influence where species, like these trees in Quebec, Canada, can thrive.


    Predicting the future

    Ecologists would also like to know how the structure of communities will shift through time. Moreover, with all the changes humans have made to the environment, restoration ecologists and conservation biologists want to predict the future of these altered communities.

    Communities are typically in flux, with some species disappearing and new ones taking hold after relatively minor disturbances. In forests, for example, when a storm knocks down a stand of trees, more light reaches the forest floor. Small, short-lived flowering plants move in, then shrubs, and tree seedlings that within a decade or so begin to shade out the herbaceous plants.

    A pioneer in the study of this process, called succession, was Frederic Clements of the University of Nebraska, Lincoln. He thought succession would inevitably lead to a particular climax community, and the system would remain in equilibrium until a disturbance started the cycle over again. Although this seems to be largely true for some plant communities, such as temperate forests, other types of communities appear to behave differently.

    In rocky intertidal communities in the Gulf of Maine, for example, the community can shift between two alternate states, dominated by either algae or mussels. Peter Petraitis of the University of Pennsylvania and Steve Dudgeon of California State University, Northridge, scraped all the life off coastal rocks in the Gulf of Maine to create patches of open habitat. As they and colleagues reported in Oecologia in April, the identity of the new community depended on which organism got there first. If mussel larvae landed, they grew faster than the algae. But if the algae had enough time to get started, they sheltered mussel predators like starfish that keep the mollusks in check.

    Although it's not known how common alternate stable states might be, the concept has important implications for restoration ecologists, who want to know whether degraded habitat will repair itself or whether it needs intervention to prevent it from falling into an undesirable new state. But there are so many variables that predicting what will happen is difficult.

    That same limitation applies to assembly rules. In a study of salt marshes published in March in Ecological Applications, a group of ecologists found that although physical stress chiefly determines the distribution of plants in a California marsh, competition is the main force in similar salt-marsh communities in Chile. The finding suggests that general rules won't provide conservation biologists with easy shortcuts when they're trying to save or restore unstudied communities.

    But Brian Silliman of the University of Florida, Gainesville, a study author, says that ecology still provides valuable insights, such as the potential impact of removing keystone predators. “We can generalize in large ways,” he says. Pimm agrees that some broad principles do exist. Although general community rules may not always provide fine-scale predictions about how a community will assemble, he says, they are “hugely useful and critical for conservation.”


    E. Connor and D. Simberloff, "The Assembly of Species Communities: Chance or Competition?" Ecology 60, 1132 (1979).

    J. Diamond, "Assembly of species communities." In Ecology and Evolution of Communities (M. L. Cody and J. M. Diamond, eds.), p. 342. Cambridge, MA: Harvard University Press (1975).

    T. Dobzhansky, "Evolution in the Tropics." American Scientist 38, 209 (1950).

    J. Fariña et al., "Can conservation biologists rely on established community structure rules to manage novel systems? ... Not in salt marshes." Ecological Applications 19, 413 (2009).

    T. Fukami et al., "Species divergence and trait convergence in experimental plant community assembly." Ecology Letters 8, 1283 (2005).


    S. Hubbell, "A unified theory of biogeography and relative species abundance and its application to tropical rain forests and coral reefs." Coral Reefs 16 (Suppl.), S9 (1997).

    A. von Humboldt and A. Bonpland, "Essay on the Geography of Plants." The University of Chicago Press (2009).

    N. Kraft et al., "Functional Traits and Niche-Based Tree Community Assembly in an Amazonian Forest." Science 322, 580 (2008).

    R. Paine, "Food Web Complexity and Species Diversity." American Naturalist 100, 65 (1966).

    P. Petraitis et al., "Experimental confirmation of multiple community states in a marine ecosystem." Oecologia 161, 139 (2009).

    J. Sanderson et al., "Pairwise co-existence of Bismarck and Solomon landbird species." Evolutionary Ecology Research 11, 771 (2009).

  9. Ardipithecus ramidus

    A New Kind of Ancestor: Ardipithecus Unveiled

    1. Ann Gibbons

    In this special issue of Science, the oldest known hominin skeleton, Ardipithecus ramidus, reveals the upright origins of humankind

    From the inside out.

    Artist's reconstructions show how Ardi's skeleton, muscles, and body looked and how she would have moved on top of branches.


    Every day, scientists add new pages to the story of human evolution by deciphering clues to our past in everything from the DNA in our genes to the bones and artifacts of thousands of our ancestors. But perhaps once each generation, a spectacular fossil reveals a whole chapter of our prehistory all at once. In 1974, it was the famous 3.2-million-year-old skeleton “Lucy,” who proved in one stroke that our ancestors walked upright before they evolved big brains.

    Ever since Lucy's discovery, researchers have wondered what came before her. Did the earliest members of the human family walk upright like Lucy or on their knuckles like chimpanzees and gorillas? Did they swing through the trees or venture into open grasslands? Researchers have had only partial, fleeting glimpses of Lucy's own ancestors—the earliest hominins, members of the group that includes humans and our ancestors (and are sometimes called hominids). Now, in a special section beginning on page 60 and online, a multidisciplinary international team presents the oldest known skeleton of a potential human ancestor, 4.4-million-year-old Ardipithecus ramidus from Aramis, Ethiopia.

    This remarkably rare skeleton is not the oldest putative hominin, but it is by far the most complete of the earliest specimens. It includes most of the skull and teeth, as well as the pelvis, hands, and feet—parts that the authors say reveal an “intermediate” form of upright walking, considered a hallmark of hominins. “We thought Lucy was the find of the century but, in retrospect, it isn't,” says paleoanthropologist Andrew Hill of Yale University. “It's worth the wait.”

    To some researchers' surprise, the female skeleton doesn't look much like a chimpanzee, gorilla, or any of our closest living primate relatives. Even though this species probably lived soon after the dawn of humankind, it was not transitional between African apes and humans. “We have seen the ancestor, and it is not a chimpanzee,” says paleoanthropologist Tim White of the University of California, Berkeley, co-director of the Middle Awash research group, which discovered and analyzed the fossils.

    Instead, the skeleton and pieces of at least 35 additional individuals of Ar. ramidus reveal a new type of early hominin that was neither chimpanzee nor human. Although the team suspects that Ar. ramidus may have given rise to Lucy's genus, Australopithecus, the fossils “show for the first time that there is some new evolutionary grade of hominid that is not Australopithecus, that is not Homo,” says paleontologist Michel Brunet of the College de France in Paris.

    In 11 papers published in this issue and online, the team of 47 researchers describes how Ar. ramidus looked and moved. The skeleton, nicknamed “Ardi,” is from a female who lived in a woodland (see sidebar, p. 40), stood about 120 centimeters tall, and weighed about 50 kilograms. She was thus as big as a chimpanzee and had a brain size to match. But she did not knuckle-walk or swing through the trees like living apes. Instead, she walked upright, planting her feet flat on the ground, perhaps eating nuts, insects, and small mammals in the woods.

    She was a “facultative” biped, say the authors, still living in both worlds—upright on the ground but also able to move on all fours on top of branches in the trees, with an opposable big toe to grasp limbs. “These things were very odd creatures,” says paleoanthropologist Alan Walker of Pennsylvania State University, University Park. “You know what Tim [White] once said: If you wanted to find something that moved like these things, you'd have to go to the bar in Star Wars.”

    Most researchers, who have waited 15 years for the publication of this find, agree that Ardi is indeed an early hominin. They praise the detailed reconstructions needed to piece together the crushed bones. “This is an extraordinarily impressive work of reconstruction and description, well worth waiting for,” says paleoanthropologist David Pilbeam of Harvard University. “They did this job very, very well,” agrees neurobiologist Christoph Zollikofer of the University of Zurich in Switzerland.

    But not everyone agrees with the team's interpretations about how Ar. ramidus walked upright and what it reveals about our ancestors. “The authors … are framing the debate that will inevitably follow,” because the description and interpretation of the finds are entwined, says Pilbeam. “My first reaction is to be skeptical about some of the conclusions,” including that human ancestors never went through a chimpanzee-like phase. Other researchers are focusing intently on the lower skeleton, where some of the anatomy is so primitive that they are beginning to argue over just what it means to be “bipedal.” The pelvis, for example, offers only “circumstantial” evidence for upright walking, says Walker. But however the debate about Ardi's locomotion and identity evolves, she provides the first hard evidence that will inform and constrain future ideas about the ancient hominin bauplan.

    Unexpected anatomy.

    Ardi has an opposable toe (left) and flexible hand (right); her canines (top center) are sized between those of a human (top left) and chimp (top right); and the blades of her pelvis (lower left) are broad like Lucy's (yellow).


    Digging it

    The first glimpse of this strange creature came on 17 December 1992 when a former graduate student of White's, Gen Suwa, saw a glint among the pebbles of the desert pavement near the village of Aramis. It was the polished surface of a tooth root, and he immediately knew it was a hominin molar. Over the next few days, the team scoured the area on hands and knees, as they do whenever an important piece of hominin is found (see story, p. 41), and collected the lower jaw of a child with the milk molar still attached. The molar was so primitive that the team knew they had found a hominin both older and more primitive than Lucy. Yet the jaw also had derived traits—novel evolutionary characters—shared with Lucy's species, Au. afarensis, such as an upper canine shaped like a diamond in side view.

    The team reported 15 years ago in Nature that the fragmentary fossils belonged to the “long-sought potential root species for the Hominidae.” (They first called it Au. ramidus, then, after finding parts of the skeleton, changed it to Ar. ramidus—for the Afar words for “root” and “ground.”) In response to comments that he needed leg bones to prove Ar. ramidus was an upright hominin, White joked that he would be delighted with more parts, specifically a thigh and an intact skull, as though placing an order.

    Filling a gap.

    Ardipithecus provides a link between earlier and later hominins, as seen in this timeline showing important hominin fossils and taxa.


    Within 2 months, the team delivered. In November 1994, as the fossil hunters crawled up an embankment, Berkeley graduate student Yohannes Haile-Selassie of Ethiopia, now a paleoanthropologist at the Cleveland Museum of Natural History in Ohio, spotted two pieces of a bone from the palm of a hand. That was soon followed by pieces of a pelvis; leg, ankle, and foot bones; many of the bones of the hand and arm; a lower jaw with teeth—and a cranium. By January 1995, it was apparent that they had made the rarest of rare finds, a partial skeleton. It is one of only a half-dozen such skeletons known from more than 1 million years ago, and the only published one older than Lucy.

    It was the find of a lifetime. But the team's excitement was tempered by the skeleton's terrible condition. The bones literally crumbled when touched. White called it road kill. And parts of the skeleton had been trampled and scattered into more than 100 fragments; the skull was crushed to 4 centimeters in height. The researchers decided to remove entire blocks of sediment, covering the blocks in plaster and moving them to the National Museum of Ethiopia in Addis Ababa to finish excavating the fossils.

    It took three field seasons to uncover and extract the skeleton, repeatedly crawling the site to gather 100% of the fossils present. At last count, the team had cataloged more than 110 specimens of Ar. ramidus, not to mention 150,000 specimens of fossil plants and animals. “This team seems to suck fossils out of the earth,” says anatomist C. Owen Lovejoy of Kent State University in Ohio, who analyzed the post-cranial bones but didn't work in the field. In the lab, he gently unveils a cast of a tiny, pea-sized sesamoid bone for effect. “Their obsessiveness gives you—this!”

    Fossil finders.

    Tim White and local Afar fossil hunters pool their finds after scouring the hillside at Aramis.


    White himself spent years removing the silty clay from the fragile fossils at the National Museum in Addis Ababa, using brushes, syringes, and dental tools, usually under a microscope. Museum technician Alemu Ademassu made a precise cast of each piece, and the team assembled them into a skeleton.

    Meanwhile in Tokyo and Ohio, Suwa and Lovejoy made virtual reconstructions of the crushed skull and pelvis. Certain fossils were taken briefly to Tokyo and scanned with a custom micro–computed tomography (CT) scanner that could reveal what was hidden inside the bones and teeth. Suwa spent 9 years mastering the technology to reassemble the fragments of the cranium into a virtual skull. “I used 65 pieces of the cranium,” says Suwa, who estimates he spent 1000 hours on the task. “You go piece by piece.”

    Once he had reassembled the pieces in a digital reconstruction, he and paleoanthropologist Berhane Asfaw of the Rift Valley Research Service in Addis Ababa compared the skull with those of ancient and living primates in museums worldwide. By March of this year, Suwa was satisfied with his 10th reconstruction. Meanwhile in Ohio, Lovejoy made physical models of the pelvic pieces based on the original fossil and the CT scans, working closely with Suwa. He is also satisfied that the 14th version of the pelvis is accurate. “There was an Ardipithecus that looked just like that,” he says, holding up the final model in his lab.

    Putting their heads together

    As they examined Ardi's skull, Suwa and Asfaw noted a number of characteristics. Her lower face had a muzzle that juts out less than a chimpanzee's. The cranial base is short from front to back, indicating that her head balanced atop the spine as in later upright walkers, rather than to the front of the spine, as in quadrupedal apes. Her face is in a more vertical position than in chimpanzees. And her teeth, like those of all later hominins, lack the daggerlike sharpened upper canines seen in chimpanzees. The team realized that this combination of traits matches those of an even older skull, 6-million to 7-million-year-old Sahelanthropus tchadensis, found by Brunet's team in Chad. They conclude that both represent an early stage of human evolution, distinct from both Australopithecus and chimpanzees. “Similarities with Sahelanthropus are striking, in that it also represents a first-grade hominid,” agrees Zollikofer, who did a three-dimensional reconstruction of that skull.

    Another, earlier species of Ardipithecus—Ar. kadabba, dated from 5.5 million to 5.8 million years ago but known only from teeth and bits and pieces of skeletal bones—is part of that grade, too. And Ar. kadabba's canines and other teeth seem to match those of a third very ancient specimen, 6-million-year-old Orrorin tugenensis from Kenya, which also has a thighbone that appears to have been used for upright walking (Science, 21 March 2008, p. 1599). So, “this raises the intriguing possibility that we're looking at the same genus” for specimens now put in three genera, says Pilbeam. But the discoverers of O. tugenensis aren't so sure. “As for Ardi and Orrorin being the same genus, no, I don't think this is possible, unless one really wants to accept an unusual amount of variability” within a taxon, says geologist Martin Pickford of the College de France, who found Orrorin with Brigitte Senut of the National Museum of Natural History in Paris.

    Dream team.

    Gen Suwa (left) in Tokyo focused on the skull; C. Owen Lovejoy (top right) in Kent, Ohio, studied postcranial bones; and Yohannes Haile-Selassie and Berhane Asfaw found and analyzed key fossils in Ethiopia.


    Whatever the taxonomy of Ardipithecus and the other very ancient hominins, they represent “an enormous jump to Australopithecus,” the next hominin in line (see timeline, p. 38), says australopithecine expert William Kimbel of Arizona State University, Tempe. For example, although Lucy's brain is only a little larger than that of Ardipithecus, Lucy's species, Au. afarensis, was an adept biped. It walked upright like humans, venturing increasingly into more diverse habitats, including grassy savannas. And it had lost its opposable big toe, as seen in 3.7-million-year-old footprints at Laetoli, Tanzania, reflecting an irreversible commitment to life on the ground.

    Lucy's direct ancestor is widely considered to be Au. anamensis, a hominin whose skeleton is poorly known, although its shinbone suggests it walked upright 3.9 million to 4.2 million years ago in Kenya and Ethiopia. Ardipithecus is the current leading candidate for Au. anamensis's ancestor, if only because it's the only putative hominin in evidence between 5.8 million and 4.4 million years ago. Indeed, Au. anamensis fossils appear in the Middle Awash region just 200,000 years after Ardi.

    Making strides

    But the team is not connecting the dots between Au. anamensis and Ar. ramidus just yet, awaiting more fossils. For now they are focusing on the anatomy of Ardi and how she moved through the world. Her foot is primitive, with an opposable big toe like that used by living apes to grasp branches. But the bases of the four other toe bones were oriented so that they reinforced the forefoot into a more rigid lever as she pushed off. In contrast, the toes of a chimpanzee curve as flexibly as those in their hands, say Lovejoy and co-author Bruce Latimer of Case Western Reserve University in Cleveland. Ar. ramidus “developed a pretty good bipedal foot while at the same time keeping an opposable first toe,” says Lovejoy.

    The upper blades of Ardi's pelvis are shorter and broader than in apes. They would have lowered the trunk's center of mass, so she could balance on one leg at a time while walking, says Lovejoy. He also infers from the pelvis that her spine was long and curved like a human's rather than short and stiff like a chimpanzee's. These changes suggest to him that Ar. ramidus “has been bipedal for a very long time.”

    Yet the lower pelvis is still quite large and primitive, similar to African apes rather than hominins. Taken with the opposable big toe, and primitive traits in the hand and foot, this indicates that Ar. ramidus didn't walk like Lucy and was still spending a lot of time in the trees. But it wasn't suspending its body beneath branches like African apes or climbing vertically, says Lovejoy. Instead, it was a slow, careful climber that probably moved on flat hands and feet on top of branches in the midcanopy, a type of locomotion known as palmigrady. For example, four bones in the wrist of Ar. ramidus gave it a more flexible hand that could be bent backward at the wrist. This is in contrast to the hands of knuckle-walking chimpanzees and gorillas, which have stiff wrists that absorb forces on their knuckles.

    However, several researchers aren't so sure about these inferences. Some are skeptical that the crushed pelvis really shows the anatomical details needed to demonstrate bipedality. The pelvis is “suggestive” of bipedality but not conclusive, says paleoanthropologist Carol Ward of the University of Missouri, Columbia. Also, Ar. ramidus “does not appear to have had its knee placed over the ankle, which means that when walking bipedally, it would have had to shift its weight to the side,” she says. Paleoanthropologist William Jungers of Stony Brook University in New York state is also not sure that the skeleton was bipedal. “Believe me, it's a unique form of bipedalism,” he says. “The postcranium alone would not unequivocally signal hominin status, in my opinion.” Paleoanthropologist Bernard Wood of George Washington University in Washington, D.C., agrees. Looking at the skeleton as a whole, he says, “I think the head is consistent with it being a hominin, … but the rest of the body is much more questionable.”

    All this underscores how difficult it may be to recognize and define bipedality in the earliest hominins as they began to shift from trees to ground. One thing does seem clear, though: The absence of many specialized traits found in African apes suggests that our ancestors never knuckle-walked.

    That throws a monkey wrench into a hypothesis about the last common ancestor of living apes and humans. Ever since Darwin suggested in 1871 that our ancestors arose in Africa, researchers have debated whether our forebears passed through a great-ape stage in which they looked like proto-chimpanzees (Science, 21 November 1969, p. 953). This “troglodytian” model for early human behavior (named for the common chimpanzee, Pan troglodytes) suggests that the last common ancestor of the African apes and humans once had short backs, arms adapted for swinging, and a pelvis and limbs adapted for knuckle walking. Then our ancestors lost these traits, while chimpanzees and gorillas kept them. But this view has been uninformed by fossil evidence because there are almost no fossils of early chimpanzees and gorillas.

    Some researchers have thought that the ancient African ape bau-plan was more primitive, lately citing clues from fragmentary fossils of apes that lived from 8 million to 18 million years ago. “There's been growing evidence from the Miocene apes that the common ancestor may have been more primitive,” says Ward. Now Ar. ramidus strongly supports that notion. The authors repeatedly note the many ways that Ar. ramidus differs from chimpanzees and gorillas, bolstering the argument that it was those apes that changed the most from the primitive form.

    But the problem with a more “generalized model” of an arboreal ape is that “it is easier to say what it wasn't than what it was,” says Ward. And if the last common ancestor, which according to genetic studies lived 5 million to 7 million years ago, didn't look like a chimp, then chimpanzees and gorillas evolved their numerous similarities independently, after gorillas diverged from the chimp/human line. “I find [that] hard to believe,” says Pilbeam.

    As debate over the implications of Ar. ramidus begins, the one thing that all can agree on is that the new papers provide a wealth of data to frame the issues for years. “No matter what side of the arguments you come down on, it's going to be food for thought for generations of graduate students,” says Jungers. Or, as Walker says: “It would have been very boring if it had looked half-chimp.”

  10. Ardipithecus ramidus

    Habitat for Humanity

    1. Ann Gibbons

    Heaps of sediment are all that's left behind from a fossil-mining operation in Aramis, Ethiopia, that yielded one of the most important fossils in human evolution, as well as thousands of clues to its ecology and environment.

    ARAMIS, ETHIOPIA—A long cairn of black stones marks the spot where a skeleton of Ardipithecus ramidus was found, its bones broken and scattered on a barren hillside. Erected as a monument to an ancient ancestor in the style of an Afar tribesman's grave, the cairn is a solitary marker in an almost sterile zone, devoid of life except for a few spindly acacia trees and piles of sifted sediment.

    That's because the Middle Awash research team sucked up everything in sight at this spot, hunting for every bit of fossil bone as well as clues to the landscape 4.4 million years ago, when Ardipithecus died here. “Literally, we crawled every square inch of this locality,” recalls team co-leader Tim White of the University of California, Berkeley. “You crawl on your hands and knees, collecting every piece of bone, every piece of wood, every seed, every snail, every scrap. It was 100% collection.” The heaps of sediment are all that's left behind from that fossil-mining operation, which yielded one of the most important fossils in human evolution (see main text, p. 36), as well as thousands of clues to its ecology and environment.

    The team collected more than 150,000 specimens of fossilized plants and animals from nearby localities of the same age, from elephants to songbirds to millipedes, including fossilized wood, pollen, snails, and larvae. “We have crates of bone splinters,” says White.

    A team of interdisciplinary researchers then used these fossils and thousands of geological and isotopic samples to reconstruct Ar. ramidus's Pliocene world, as described in companion papers in this issue (see p. 66 and 87). From these specimens, they conclude that Ardi lived in a woodland, climbing among hackberry, fig, and palm trees and coexisting with monkeys, kudu antelopes, and peafowl. Doves and parrots flew overhead. All these creatures prefer woodlands, not the open, grassy terrain often conjured for our ancestors.

    The team suggests that Ar. ramidus was “more omnivorous” than chimpanzees, based on the size, shape, and enamel distribution of its teeth. It probably supplemented woodland plants such as fruits, nuts, and tubers with the occasional insects, small mammals, or bird eggs. Carbon-isotope studies of teeth from five individuals show that Ar. ramidus ate mostly woodland, rather than grassland, plants. Although Ar. ramidus probably ate figs and other fruit when ripe, it didn't consume as much fruit as chimpanzees do today.

    Past and present.

    Ardipithecus's woodland was more like Kenya's Kibwezi Forest (left) than Aramis today.


    This new evidence overwhelmingly refutes the once-favored but now moribund hypothesis that upright-walking hominins arose in open grasslands. “There's so much good data here that people aren't going to be able to question whether early hominins were living in woodlands,” says paleoanthropologist Andrew Hill of Yale University. “Savannas had nothing to do with upright walking.”

    Geological studies indicate that most of the fossils were buried within a relatively short window of time, a few thousand to, at most, 100,000 years ago, says geologist and team co-leader Giday WoldeGabriel of the Los Alamos National Laboratory in New Mexico. During that sliver of time, Aramis was not a dense tropical rainforest with a thick canopy but a humid, cooler woodland. The best modern analog is the Kibwezi Forest in Kenya, kept wet by groundwater, according to isotope expert Stanley Ambrose of the University of Illinois, Urbana-Champaign. These woods have open stands of trees, some 20 meters high, that let the sun reach shrubs and grasses on the ground.

    Judging from the remains of at least 36 Ardipithecus individuals found so far at Aramis, this was prime feeding ground for a generalized early biped. “It was the habitat they preferred,” says White.

  11. Ardipithecus ramidus

    The View From Afar

    1. Ann Gibbons

    How do you find priceless hominin fossils in a hostile desert? Build a strong team and obsess over the details

    The crawl.

    Researchers hunt down every fossil at Aramis.


    MIDDLE AWASH VALLEY, THE AFAR DEPRESSION, ETHIOPIA—It's about 10 a.m. on a hot morning in December, and Tim White is watching a 30-year-old farmer inch his way up a slippery hill on his knees, picking through mouse-colored rubble for a bit of gray bone. The sun is already bleaching the scrubby badlands, making it difficult to distinguish a fragment of bone in the washed-out beige and gray terrain. The only shade in this parched gully is from a small, thorny acacia tree, so the fossil hunters have draped their heads with kerchiefs that hang out from under their “Cal” and “Obama for President” baseball caps, making them look like a strange tribe of Berkeley Bedouins. If there are fossils here, White is confident that the slender farmer, Kampiro Kayrento, will find them. “Kampiro is the best person in the world for finding little pieces of fossilized human bone,” says White, 59, a paleoanthropologist at the University of California, Berkeley, who has collected fossils in this region since 1981.

    Watching Kayrento is a sort of spectator sport, because he scores so often. Just minutes earlier, he had walked over the crest of a small hill, singing softly to himself, and had spotted the fossilized core of a horn from an ancient bovid, or antelope. Then he picked up a flat piece of gray bone nearby and showed the fossil to Ethiopian paleoanthropologist Berhane Asfaw, asking, “Bovid?” Asfaw, 55, who hired Kayrento when he was a boy hanging out at fossil sites in southern Ethiopia, looked over the slightly curved piece of bone the size of a silver dollar and suggested, “Monkey?” as he handed it to White. White turned it over gently in his hands, then said: “Check that, Berhane. We just found a hominid cranium. Niiiice.”

    Ancestral territory.

    The area where Ardi was found is rich in hominin fossil sites, including these worked by the Middle Awash research team.


    As word spreads that Kayrento found a hominin, or a member of the taxon that includes humans and our ancestors, the other fossil hunters tease him: “Homo bovid! Homo bovid! Niiiice.”

    The Middle Awash project, which includes 70 scientists from 18 nations, is best known for its discovery of the 4.4-million-year-old partial skeleton of Ardipithecus ramidus at Aramis, about 34 kilometers north of here. That skeleton is now dramatically revising ideas of how upright walking evolved and how our earliest ancestors differed from chimpanzees (see overview, p. 60, and main Focus text, p. 36). But Aramis is just one of 300 localities in the Middle Awash, which is the only place in the world to yield fossils that span the entire saga of hominid evolution. At last count, this team had gathered 19,000 vertebrate fossils over the past 19 years. These include about 300 specimens from seven species of hominins, from some of the first members of the human family, such as 5.8-million-year-old Ar. ramidus kadabba, to the earliest members of our own species, Homo sapiens, which lived here about 160,000 years ago.

    As they work in different places in the valley, the team members travel back and forth in time. Today, this core group is working in the western foothills near the Burka catchment, where an ancient river laid down sediments 3 million to 2 million years ago and where the team has found specimens of Australopithecus garhi, a species they suspect may have given rise to the first members of our genus, Homo.

    This season, after a rough start, the 25 scientists, students, cooks, and Ethiopian and Afar officials and guards in camp are working well together. Their tented camp is hours from any town, graded road, or fresh water. (They dug their own well to get water.) “The 1st week, it's like an engine that's running but not running smoothly,” says White, who, with Asfaw, runs a well-organized camp where every tool, map, and shower bag has its proper place. “By the 3rd week, people know their jobs.”

    The 1st week, White and a paleontologist were sick, and White is still fighting a harsh cough that keeps him awake at night. The 2nd week, some aggressive Alisera tribesmen who live near the Ar. ramidus site threatened to kill White and Asfaw, making it difficult to return there. (That's one reason the team travels with six Afar policemen armed with AK-47s and Obama caps, dubbed “The Obama Police.”) The day before, a student had awakened with a high fever and abdominal pain and had to be driven 4 hours to the nearest clinic, where he was diagnosed with a urinary tract infection, probably from drinking too little water in the 35°C heat. “The best laid plans change every day,” says White, who has dealt with poisonous snakes, scorpions, malarial mosquitoes, lions, hyenas, flash floods, dust tornadoes, warring tribesmen, and contaminated food and water over the years. “Nothing in the field comes easy.”

    Division of labor.

    Kampiro Kayrento (top left) homes in on fossils; he and others sweep the surface, and Giday WoldeGabriel dates sediments.


    Calling the “A” team

    Nothing in the Afar, for that matter, comes easy. We are reminded of that as we drive across the dusty Saragata plain to the target fossil site at 8 a.m., making giant circles in the dust with the Toyota Land Cruiser so we can find our tracks home at the end of the day. Men clad in plaid wraps, with AK-47s slung over their shoulders, flag us down seeking help. They bring over a woman who looks to be in her 70s but is probably much younger. Her finger is bleeding, and the men tell White and Asfaw, in Afar, that a puff adder bit her the night before while she was gathering wood. A quick-thinking boy had sliced her finger with a knife, releasing the venom and probably saving her life. White gets out a first-aid kit, removes a crude poultice, and cleans and bandages the wound, putting on an antibiotic cream. “It's good she survived the night,” he says as we drive off. “The danger now is infection.”

    After inching down the sandy bank of a dry river, we reach the so-called Chairman's site. This is one of dozens of fossil localities discovered in the Burka area since 2005: exposed hillsides that were spotted in satellite and aerial photos, then laboriously explored on foot. The plan was to search for animal fossils to help date a hominid jawbone discovered last year. But in the 1st hour, with Kayrento's discovery, they're already on the trail of another individual instead.

    As soon as White identifies the bit of skull bone, he swings into action. With his wiry frame and deep voice, he is a commanding presence, and it soon becomes clear how he earned his nickname, “The General.” In his field uniform—a suede Australian army hat with a rattlesnake band, blue jeans, and driving gloves without fingers—he uses a fossil pick to delineate the zones in the sandstone where he wants the crew deployed. “Get everybody out of the area,” he calls to the 15 people already fanned out over the gully, scanning for fossils. “I want the ‘A’ team.” He singles out Kayrento and three others and hands them yellow pin-flags, saying, “Go back to the bottom.” As he watches them move up the slope, he warns: “Go slowly. You're moving too fast. … Don't squash the slope. Move like a cat, not a cow.”

    By looking at the relatively fresh fractured edge of the bone fragment, White knows that it comes from a larger piece of skull that broke after it was exposed, not while it was buried. As Kayrento and the others find other bits of bone, they place yellow pin-flags at those spots. “This process establishes the distributional cone,” White explains. The top flag marks the highest point on the surface where the skull came out of the ground; the bottom boundary marks the farthest point where a fragment might finally have come to rest, following the fall line down the slope.

    This discovery also illustrates one reason why the team comes to the field right after the rainy season. If they're lucky, rain and floods will cut into the ancient sediments, exposing fossils. But they have to get there before the fossils disintegrate as they are exposed to the elements or are trampled by the Afar's goats, sheep, and cattle. Timing is everything, and this season they're a bit late. “The ideal situation is to find a fossil just as it is eroding out of the bank,” says White.

    As they crawl the entire length of the gully, they turn over every rock, mud clod, and piece of carbonate rubble to make sure it doesn't contain a fossil fragment. “Not good,” says Kayrento. “This is yucky,” agrees Asfaw, co-director of the team and the first Ethiopian scientist to join it, in 1979 when he was invited to earn his Ph.D. at Berkeley (Science, 29 August 2003, p. 1178).

    After 2 hours, the team has collected a few more pieces of skull around the temple, forehead, and ear. “It's getting bigger by the minute,” White says. “If we're lucky, we'll find it buried right in here.”

    The team has to wait until the next day to find out just how lucky. At 9:45 a.m. Thursday, they return with reinforcements: Asfaw has hired two Afar men to help with the heavy lifting of buckets of dirt. With a button-down Oxford cloth shirt and a pistol stuck in the waist-band of his khakis, Asfaw commands respect, and he is the best at negotiating with the Afar. In this case, he settles an argument by letting clan leaders select which men, among a large group, will get jobs.

    At the site, White sets up a perimeter of blue pin-flags that look like a mini slalom course, outlining the gully that he calls the “Hot Zone” where fossil pieces are most likely to be buried. The plan is to excavate all the rock and dirt around those flags, down to the original layers of sediment. White explains that the ancient landscape would have been flatter and more verdant before tectonic movements of Earth's crust cracked and tilted the sediment layers. But the original soil is still there, a red-brown layer of clay beneath a gray veneer of sandstone. “Throw every piece of stone out of the channel,” he orders. “If you see a hominid, I need to know right away!”

    White and Kayrento literally sweep off the gray lag with a push broom and then scrape back the layers of time with a trowel to the ancient surface underneath. “Once we brush out the slopes, we'll be sure no fossil is left in place,” says White. In case they miss a fragment, the loose sediment is carried to giant sieves where the crew sifts it for bits of bone or teeth. The sifted rubble is taken to a circle of workers who then empty it into small aluminum pans, in which they examine every single, tiny piece—a job that gives new meaning to the word tedium. “Sieving 101,” observes Asfaw, who supervises sieving and picking today.

    By 11:10 a.m., the pace of discovery has slowed. When the A team tells White it's “not good,” he tries to infuse them with some of his energy, reminding everyone to stay focused, to keep going, to not step on fossils. But by midday, White is grumbling, too, because they've scoured the Hot Zone and it's clear the skull is not there. “We've eliminated every hope of finding it in situ.”

    Time travel

    It's a good time to take a walk with the four geologists, who are combing the terrain, hoping to find sediments with volcanic minerals to help them date the locality and its fossils precisely. While fossil hunters move slowly, stooped at the waist and focused on the ground, the geologists move fast, heads up, scanning the next horizon for a rock face with a layer cake of sediments, like those exposed in road cuts. The 6-million-year record of Middle Awash sediments is not stacked neatly in one place, with oldest rocks on the bottom and youngest on top. (If it were, the stack would be 1 kilometer thick.) Instead, the rocks are faulted and tilted into different ridges. By tracing a once-horizontal layer from ridge to ridge, sometimes for kilometers, the geologists can link the layers and place different snapshots of time into a sequence.

    Today, Ethiopian geologist Giday WoldeGabriel of the Los Alamos National Laboratory in New Mexico, also a co-leader of the team (he joined in 1992), is searching for a familiar-looking motif—a distinct layer of volcanic tuff called the SHT (Sidiha Koma Tuff), previously dated to 3.4 million years ago by radiometric methods.

    So far, the team has found just one species of hominin—Au. garhi—that lived at this time in the Middle Awash (Science, 23 April 1999, p. 629), although a more robust species, Au. aethiopicus, appears 2.6 million years ago in southern Ethiopia and Kenya. That's also when the earliest stone tools appear in Gona, Ethiopia, 100 kilometers north of here. The earliest fossils of our genus Homo come a bit later—at 2.3 million years ago at Hadar, near Gona, also with stone tools. That's why it is important to date Au. garhi precisely: Was it the maker of the stone tools left in the Afar? The team thinks Au. garhi is the direct descendant of the more primitive Au. afarensis, best known as the species that includes the famous 3.2-million-year-old skeleton of Lucy, also from Hadar. But did Au. garhi then evolve into early Homo? They need better dates—and more fossils—to find out.

    “Now that we have the SHT as a reference point here, we have to try to trace it to where the new fossils are,” says WoldeGabriel. The only problem is that the SHT is several ridges and basins over from the excavation; linking the two will be difficult if not impossible. The team will also use other methods to date the new fossils. Luckily, the fossil hunters have found a pig known to have lived about 2.6 million to 2.7 million years ago, which suggests that the sediments and the new discovery are also that old.

    Intensive care.

    Tim White uses dental tools and a gluelike adhesive to extract fragile fossils from matrix.


    At 9 a.m. Friday, 12 December, we're back at the Chairman's site for a 3rd day, this time with a film crew from Sweden. After White and Kayrento jokingly reenact the discovery of the skull bone for the film crew, they resume sweeping and sifting, exactly where they left off. At first, there's little return. Berkeley postdoc Cesur Pehlevan from Ankara hands White a piece of bone: “Nope, tough luck. Right color, right thickness. Nope, sorry.”

    Finally, someone hands White something special. “Oh nice, frontal bone with frontal sinus. This is getting better. That's what we're after,” says White. “If we can get that brow ridge, we can match it with the known species.” He turns over the new piece of frontal bone in his hand, examining it like a diamond dealer assessing a gemstone.

    By the end of 3 days, the team of 20 will have collected a dozen pieces of one skull, an average yield for this region. Taken together, says White, those pieces show that “It's an Australopithecus because it has a small braincase, small chewing apparatus.” There's still not enough to identify the species, though White thinks it is Au. garhi. He notes that “it's a big boy, big for an australopithecine.” If it is Au. garhi, that would be one more bit of evidence to suggest that Au. afarensis gave rise to Au. garhi; males are bigger than females in Au. afarensis—and so perhaps in Au. garhi, too.

    For now, White and Asfaw are pleased with the new snapshot they're getting of Au. garhi. On our way back to camp, White stops so we can take a photo of the moon rising over Yardi Lake in front of us, the sun setting behind us. The landscape has changed since the australopithecines were here. But one thing's been constant in the Middle Awash, he notes: “Hominids have been right here looking at the moon rising over water for millions of years.”

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