Warfare was uncommon among hunter-gatherers, and killings among nomadic groups were often due to competition for women or interpersonal disputes, researchers in Finland said Thursday.

Their study in the U.S. journal Science suggests that the origins of war were not -- as some have argued -- rooted in roving hunter-gather groups but rather in cultures that held land and livestock and knew how to farm for food.

Two NASA spacecraft are about to take pictures of the Earth for planetary science research, and the U.S. space agency is encouraging people worldwide to jump into the shot.

"Consider it the first interplanetary photobomb," NASA said.

Deforestation has soared in the Brazilian Amazon since a new forestry code was passed last year at the urging of the agribusiness lobby, a non-profit environmental group said Thursday.

Between August 2012 and June 2013, 1,838 square kilometers (709 square miles) of forest were lost, a 103 percent hike over the same previous period, Institute Imazon said in its latest report.

Gene scientists on Wednesday said that in lab-dish cells, they had found a way to switch off the rogue chromosome that causes Down's syndrome.

The breakthrough opens up the tantalising goal of therapy for Down's, they said, cautioning that years of work lie ahead before this aim is reached -- if, in fact, it is attainable.

Long-necked plant-grazing dinosaurs that roamed the Earth 150 million years ago evolved a nifty way of fixing broken teeth. They just grew new ones, said a U.S. study Wednesday.

Scientists analyzed the fossils of two of the largest herbivores known to have lived in North America -- Diplodocus and Camarasaurus -- and found they grew fresh smiles every six weeks or so.

A strange glow in space has provided fresh evidence that all the gold on Earth was forged from ancient collisions of dead stars, researchers reported Wednesday.

Astronomers have long known that fusion reactions in the cores of stars create lighter elements such as carbon and oxygen, but such reactions can't produce heavier elements like gold.

Australia pledged another Aus$5 million (U.S.$4.6 million) to the fight against a predatory starfish devastating the iconic Great Barrier Reef Thursday, revealing 100,000 of the creatures had been wiped out so far.

Environment Minister Mark Butler said the new funding, on top of Aus$2.53 million already pledged, would support a program of culling the coral-eating crown-of-thorns starfish, which is naturally-occurring but has proliferated due to pollution and run-off.

A giant panda gave birth to twins at an American zoo this week -- the first panda double birth in the U.S. in 26 years.

Mama Lun Lun and her cubs, which were delivered Monday, are doing well, according to Zoo Atlanta in the southern state of Georgia.

Medical research that uses animals to test therapies for human brain disorders is often biased, claiming positive results and then failing in human trials, U.S. researchers said Tuesday.

The findings by John Ioannidis and colleagues at Stanford University could help explain why many treatments that appear to work in animals do not succeed in humans.

Palaeontologists in Utah on Wednesday said they had found the fossil of a strange horned dinosaur which roamed an island continent known as Laramidia.

Dubbed Nasutoceratops titusi, the creature lived during the Late Cretaceous about 76 million years ago.