Doubts have been raised about one of Europe's most talked about ancient DNA results, the mtDNA haplogroup H sequence from the Paglicci Cave remains. A preprint at Current Biology suggests the Paleolithic sample was contaminated with modern DNA:
To further evaluate the authenticity of the ancient DNA we calculated the proportion of nucleotide misincorporations arising from DNA damage, a quantity that is known to increase over time after the death of an individual  and has been used as an indication of authenticity in previous work . It was suggested that bone samples 100 years and older have a minimum of 20% C to T misincorporations concentrated at the 50 end of the molecule . Using this criterion, we excluded Paglicci Str. 4b from further analysis as the rate of C to T misincorporation at the 50 end was only 8.8%, thus making an ancient origin for the DNA in this sample uncertain .Another sample thought to be from a Paleolithic European, dubbed "Cro-Magnon 1" and belonging to haplogroup T2b1, was also eliminated from the study after radiocarbon dating revealed it to be of medieval origin. What this means is that all Paleolithic European remains successfully tested to date belong to mtDNA haplogroup U, including six new samples featured in this paper.
It has been argued that hg U5 is the most ancient subhaplogroup of the U lineage, originating among the first early modern humans in Europe . Our results support this hypothesis because we find that the two Dolni Vestonice individuals radiocarbon dated to 31.5 kya carry a type of mtDNA that is as yet uncharacterized, sits close to the root of hg U, and carries two mutations that are specific to hg U5. With our recalibrated molecular clock, we date the age of the U5 branch to approximately 30 kya, thus predating the LGM. Because the majority of late Paleolithic and Mesolithic mtDNAs analyzed to date fall on one of the branches of U5 (see also ), our data provide some support for maternal genetic continuity between the pre- and post-ice age European hunter-gatherers from the time of first settlement to the onset of the Neolithic.A Revised Timescale for Human Evolution Based on Ancient Mitochondrial Genomes, Current Biology (2013), http://dx.doi.org/10.1016/j.cub.2013.02.044