The journal Science has named the discovery of Ardi, the fossilized partial skeleton of a female ground ape that lived 4.4 million years ago, as the biggest scientific breakthrough of 2009.
Scientists said Ardipithecus ramidus was an early member of the human branch of the primate family tree, predating the famous Lucy, found in 1974, by more than one million years.
Ardi isn't the final ancestor shared by humans and chimpanzees — that lived at least six million years ago — but it's the closest to it that paleontologists have seen.
The Ardi 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," wrote Bruce Alberts, editor in chief of Science.
Ardi surprised scientists because many of her traits don't appear in living African apes or in humans, suggesting that both the human branch and the ape branch of the family tree had already evolved significantly from their common ancestor by the time she lived.
Some scientists said Ardi disproves the "missing link," the idea that humans evolved from a common ancestor that looks like a modern-day chimpanzee.
"From studying Ardipithecus ramidus, or Ardi, we learn that we cannot understand or model human evolution from chimps and gorillas," said Owen Lovejoy, a lead author of one of the 11 studies of Ardi that appeared in Science.
The rest of the Science magazine Top 10 breakthroughs of the year:
- The discovery of 16 previously unknown pulsars — rapidly rotating neutron stars — by an international team of astronomers using NASA's Fermi Gamma-Ray Space Telescope. The discovery added to physicists' understanding of the strong magnetic fields pulsars produce.
- The longevity-boosting compound rapamycin, a secretion of soil bacteria from Easter Island, shown to stretch the lifespans of experimental mice by nine to 14 per cent.
- Experimental electronic devices made from graphene, single-atom-thick sheets of carbon that allow electrons to move incredibly fast. Graphene enables electronics to be made very thin, flexible and stretchable.
- The discovery of receptors in plant cells for abscisic acid, a chemical that allows seeds to remain dormant and keeps plants from losing water during periods of drought. Exploiting this finding could improve crop yields and allow farming on land previously thought to be too dry.
- The first X-ray laser, built at the SLAC National Accelerator Laboratory in Menlo Park, Calif. The Linac Coherent Light Source, powered by a three-kilometre-long linear accelerator, can take snapshots of chemical reactions.
The use of gene therapy to cure a rare fatal brain disease, inherited blindness and an immune disorder known as Bubble Boy disease.
The creation of "quasiparticles" with only one magnetic pole, which had been predicted by physicists' models but never seen in nature. Every magnet ever seen before has a north and south pole, but theory indicated the poles should be able to exist on their own. Physicists created the monopoles in an exotic super-cooled form of matter called spin ices.
- NASA's deliberate crashing of the LCROSS satellite and its burned-out rocket tube into the moon in October, confirming the presence of water there. "There's not just water, but lots of water," said Anthony Colaprete, a scientist on the project.
- The in-orbit repair of the Hubble space telescope by the crew of the space shuttle Atlantis, leading to the best images yet from the 19-year-old satellite. Over 11 days and five spacewalks, astronauts replaced the satellite's camera, batteries and gyroscopes and installed new instruments.