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The research that brought to light the fossils of Ardipithecus ramidus, a hominid species that lived 4.4 million years ago in what is now Ethiopia, has topped Science's list of this year's most significant scientific breakthroughs. The monumental find predates "Lucy,"--previously the most ancient partial skeleton of a hominid on record--by more than one million years, and it inches researchers ever-closer to the last common ancestor shared by humans and chimpanzees.

Science and its publisher, AAAS, the nonprofit science society, recognize the Ardipithecus ramidus fossils, including the partial skeleton named "Ardi," as 2009's Breakthrough of the Year. They also identify nine other important scientific accomplishments from this past year in a top ten list, appearing in a special news feature in the journal's 18 December 2009 issue.

The Ardipithecus research "changes the way we think about early human evolution, and it represents the culmination of 15 years of painstaking, highly collaborative research by 47 scientists of diverse expertise from nine nations, who carefully analyzed 150,000 specimens of fossilized animals and plants," said Dr. Bruce Alberts, editor-in-chief of Science, in a related editorial.

Back in October, an international team of scientists offered this first comprehensive, peer-reviewed description of Ardipithecus. This research appeared in a special issue of Science, published on 2 October 2009 (http://www. sciencemag. org/ ardipithecus/ ). Until then, the fossil record contained only scant evidence of other hominids older than "Lucy."

After analyzing the skull, teeth, pelvis, hands, feet, and other bones, they determined that Ardipithecus possessed a mix of "primitive" traits, shared with its predecessors--the apes of the Miocene epoch--and "derived" traits, which it shared exclusively with later hominids.

However, many of its traits do not appear in modern-day African apes. One surprising conclusion, therefore, is that it is likely that the African apes have evolved extensively since we shared that last common ancestor, which thus makes living chimpanzees and gorillas poor models for the last common ancestor and for understanding our own evolution since that time.

The first Ardipithecus fossils were actually dug up in 1994, but the team of researchers responsible for their discovery was careful not to rush the findings to the public. Instead, more than a decade of detailed analysis and documentation followed, as the experts sent their fossils to various laboratories around the world for evaluation. This collaborative, international effort to study "Ardi" and her environment represents a major scientific landmark of both discovery and analysis.

Science's list of the nine other groundbreaking achievements from 2009 follows.

Pulsars Detected by Fermi: NASA's Fermi Gamma-Ray Space Telescope helped to identify previously unknown pulsars--highly magnetized and rapidly rotating neutron stars--and shed light onto their unique gamma-ray emissions.

Rapamycin: Researchers found that tinkering with a key signaling pathway produces life-extending benefits in mice--the first such result ever achieved in mammals. The discovery was particularly remarkable because the treatment did not start until the mice were middle-aged.

Graphene: In a string of rapid-fire advances, materials scientists probed the properties of graphene--highly conductive sheets of carbon atoms--and started fashioning the material into experimental electronic devices.

Plant ABA Receptors: Solving the structure of a critical molecule that helps plants survive during droughts may help scientists design new ways to protect crops against prolonged dry periods, potentially improving crop yields worldwide and aiding biofuel production on marginal lands.

LCLS at SLAC: SLAC National Accelerator Laboratory unveiled the world's first x-ray laser, a powerful research tool capable of taking snapshots of chemical reactions in progress, altering the electronic structures of materials, and myriad other experiments spanning a wide range of scientific fields.

Gene Therapy Comeback: European and U.S. researchers made progress in treating a fatal brain disease, inherited blindness, and a severe immune disorder by developing new strategies involving gene therapy.

Monopoles: In an experimental coup, physicists working with strange crystalline materials called spin ices created magnetic ripples that model the predicted behavior of "magnetic monopoles," or fundamental particles with only one magnetic pole.

LCROSS Finds Water on the Moon: In October, sensors aboard a NASA spacecraft detected water vapor and ice in the debris from a spent rocket stage that researchers deliberately crashed near the south pole of the Moon.

Hubble Repair: In May, a nearly flawless final repair mission by space-shuttle astronauts gave the Hubble Space Telescope sharper vision and a new lease on life, resulting in its most spectacular images yet.

Areas to Watch: Science's predictions for hot science topics in 2010 include cancer cell metabolism, the Alpha Magnetic Spectrometer, exome sequencing and disease, pluripotent stem cells for neuropsychiatric disease, and the future of human space flight.

The special news feature will also revisit last year's Breakdown of the Year--the financial meltdown--and explore the effects of this year's Virus of the Year--H1N1 flu--on scientific research and collaborations.

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On the afternoon of Thursday, December 17, the Breakthrough of the Year articles, plus a related editorial by Bruce Alberts, Science's editor-in-chief, and related multimedia will be available at http://www. sciencemag. org/ btoy2009/ .

The American Association for the Advancement of Science (AAAS) is the world's largest general scientific society, and publisher of the journal, Science (www.sciencemag.org) as well as Science Translational Medicine (www.sciencetranslationalmedicine.org) and Science Signaling (www.sciencesignaling.org). AAAS was founded in 1848, and includes some 262 affiliated societies and academies of science, serving 10 million individuals. Science has the largest paid circulation of any peer-reviewed general science journal in the world, with an estimated total readership of 1 million. The non-profit AAAS (www.aaas.org) is open to all and fulfills its mission to "advance science and serve society" through initiatives in science policy; international programs; science education; and more. For the latest research news, log onto EurekAlert!, www.eurekalert.org, the premier science-news Web site, a service of AAAS.