WASHINGTON, Nov. 24 -- Northern China may have served as an early center of chicken domestication, possibly dating as far back as 10,000 years, researchers from China and Germany said Monday.

Some scientists, including Charles Darwin, have suggested that chicken domestication originated about 4,000 years ago in the Indus Valley, South Asia. However, more recent research suggested that chickens were domesticated multiple times in different parts of Asia, including regions in South Asia, Southwest China, and Southeast Asia.

The bones of chickens dating to more than 10,000 years before present have been discovered in China, but it is unclear whether the specimens are related to present-day domestic species.

In the new study, professor Xingbo Zhao of China Agricultural University, and colleagues chose 39 ancient chicken bones from Cishan, Nanzhuangtou, and Wangyin, three archaeological sites representing the earliest sites for chicken bones both in northern China and worldwide, as well as one younger archaeological site known as Jiuliandun Chu Tombs for ancient DNA analyses.

The bones range in age from 2,300 to 10,500 years ago, based on a technique called radiocarbon dating, the researchers said.

The researchers then compared mitochondrial DNA sequences from the ancient bones with those from modern ground-feeding birds from the Galliformes order, including pheasants, rock partridges and chickens, as well as those from ancient specimens from Spain, Hawaii, Chile, and Easter Island.

Their analysis showed that the chicken bones from northern China belong to the genus Gallus which includes modern domesticated chickens.

"Combined phylogenetic analyses on modern and ancient DNA sequences from all over the world have supported the hypothesis of multiple maternal chicken origins in South and Southeast Asia," said the study published in the U.S. journal Proceedings of the National Academy of Sciences.

"Our results now add northern China as another center of chicken domestication within Asia."

The study also included researchers from China's Hebei Provincial Institute of Cultural Relic, Hebei's Xushui County Office for Preservation of Ancient Monuments, Jilin University, and University of Potsdam in Germany.