New technique for dating ancient skeletons
Dating of ancient bones using DNA mutations could provide a fast and cheap alternative to current methods.
A new analytic technique – time population structure (TPS) – allows accurate dating of skeletons using DNA mutations, linked to geography, to estimate age.
The method, developed by a team in the Department of Animal and Plant Sciences at the University of Sheffield, UK, could be used to improve knowledge of ancient migration patterns, genealogy, and health research, offering insight into the link between ancestry and population stratification and genetic disorders.
This technique is based on the knowledge that people living in the same time period have a similar geo-chronological genetic structure. Umberto Esposito, a Research Associate at the Sheffield Bioinformatics Hub, Department of Animal and Plant Sciences at the University of Sheffield, told Materials World, ‘It is established that human DNA contains mutations that are connected to geography – called ancestry informative markers. That is, small differences in the genetic structure, specifically in the alleles [variant forms of a particular gene] frequencies of specific DNA positions, which allow us to infer the place of origin of the DNA carried by the individual. We, therefore, formulated the hypothesis that analogous differences in the DNA exist and can be representative of the time when the individual lived.’
Most alleles not subject to selection mutate by chance, with their frequencies the result of demographic processes that change over time, according to Esposito. These time-dependent events create signatures that can be observed.
DNA samples dated using radiocarbon dating were used to train the team’s technique. Computational methods were applied to DNA from 800 skeletons – living between 40,000 and 1,500 years ago in Europe and Asia – with known radiocarbon dates, allowing the team to build up data in which skeletons with similar age and genetic profile were grouped. This data was used as a reference point, allowing the age of an unknown sample to be determined by comparing it against known samples, assessing the geo-chronological genetic similarity.
Fast and cheap
This technique could also be used to complement radiocarbon dating – a traditional method used to date organic matter by measuring the levels of carbon isotopes it contains – or as an alternative method.
‘Radiocarbon dating is a widespread and very valuable technique that is still the best method that we have to date skeletons,’ said Esposito. ‘It is, however, a limited procedure. Unfortunately, in many cases the level of radiocarbon on these skeletons is not enough to be able to apply the dating method.’ The DNA-based TPS technique does not rely on radiocarbon levels.
Esposito added, ‘[TPS’s] great advantage is that it can offer a fast and cheap alternative to radiocarbon dating.’ At the time of writing, the team are preparing a paper on dating skeletons using TPS.
Upper Palaeolithic to the Early Middle Ages
At its current stage, the technique has shown similar results to those attained from radiocarbon dating – predictions on samples up to 45,000 years old from both techniques had an average difference of 800 years.
The team are compiling a larger dataset, improving both geographical and time coverage. Esposito said, ‘we are including newly published data that will allow us to obtain a better coverage of Eurasia and of time periods going form the Upper Palaeolithic to the Early Middle Ages (roughly from 40,000 to 1,500 years ago). In principle, the method can be extended worldwide once sufficient DNA are available.’
A method to infer the geographical origin of skeletons’ DNA is also being developed by the team, giving insight into early migration routes.