A study of DNA from ancient farmers in Europe shows sharp differences from that of modern Europeans — results that are likely to add fuel to the debate over European origins.

Researchers led by Wolfgang Haak of Johannes Gutenberg University in Mainz, Germany, argue that their finding supports the belief that modern residents of central Europe descended from Stone Age hunter-gatherers who were present 40,000 years ago, and not the early farmers who arrived thousands of years later.

But other anthropologists questioned that conclusion, arguing that the available information isn't sufficient to support it.

Haak's team used DNA from 24 skeletons of farmers from about 7,500 years ago, collected in Germany, Austria and Hungary. Six of the skeletons — 25 percent — belonged to the "N1a" human lineage, according to genetic signatures in their mitochondrial DNA, which is inherited from the mother.

The N1a marker is extremely rare in modern Europeans, appearing in just 0.2 percent.

"This was a surprise. I expected the distribution of mitochondrial DNA in these early farmers to be more similar to the distribution we have today in Europe," co-author Joachim Burger, also from Johannes Gutenberg University, said in a statement.

"Our paper suggests that there is a good possibility that the contribution of early farmers could be close to zero," added co-author Peter Forster from the University of Cambridge in England.

Absence of the marker in modern people indicates they are descended from ancient hunter-gatherers rather than the later-arriving farmers, the researchers said.

But others challenged that conclusion.

"The data are new, the analysis is not compelling, and the conclusions are illogical," said anthropologist Milford H. Wolpoff of the University of Michigan.

Anthropologist Joao Zilhao of the University of Bristol, England, noted that the study didn't compare the DNA of the ancient farmers with that of the ancient hunter-gatherers, adding that there are plenty of hunter-gatherer burials in German cave sites that could have been sampled for comparison.

Without that comparison it's hard to say that the difference between modern DNA and that of the ancient farmers means current people are descended from the ancient hunter-gatherers.

"In this particular case, the reason may be because of a farmer input that was subsequently diluted, assuming that the N1a haplotype is a marker of spreading farmers, and that it was as rare in pre-Neolithic Europe as it is today," Zilhao said.

But, he added, "I see nothing in the data that would necessarily carry the exclusion of, for instance, the opposite hypothesis ... that (the N1a marker) represents the incorporation of hunter-gatherer females in the farming communities that are coming into Europe about 7,500 years ago, that incorporation being in such small numbers that, eventually, it all but disappeared."

The research was funded by the German Federal Ministry for Education and Research.