Neanderthals were not wiped out by modern human ancestors but more likely were integrated into the human gene pool thousands of years ago, U.S. researchers say.

Responding to a growing ice age, Neanderthals and modern human ancestors expanded their territorial ranges across Asia and Europe to adapt to the changing environment and in the process encountered each other, Arizona State University researcher C. Michael Barton said.

As cultural and climatic forces brought the two groups together, Barton said, the Neanderthals demise was due to a combination of influences including cultural changes and interbreeding, Barton said.

As Neanderthals' and early humans' land-use patterns shifted during the ice age, computer modeling shows the two populations began to interact culturally and mate, leading to the "extinction" of one of the groups due to hybridization, a well-recognized phenomenon in conservation biology, an ASU release said.

Neanderthals were limited to western Eurasia and usually it is the smaller population that becomes "extinct" in this way, the researchers said.

Nevertheless, succeeding hybrid populations still carry genes from the regional group that disappeared, researchers said.

This has been confirmed by genetic studies in modern populations carried out by Julien Riel-Salvatore of the University of Colorado, Denver.

"Recent sequencing of ancient Neanderthal DNA indicates that Neanderthal genes make up from 1 to 4 percent of the genome of modern populations -- especially those of European descent," Riel-Salvatore said.

"While they disappeared as a distinctive form of humanity, they live on in our genes."