When we research human migration in the past, it is a challenge to pinpoint where exactly different individuals and groups came from. A new study published in PLOS ONE describes a new method to accurately identify the origins of individual humans using archaeological remains. In an interdisciplinary effort, the NEXUS1492 team members Dr. Jason Laffoon, Dr. Till Sonnemann and Dr. Termeh Shafie, in collaboration with the nexus principal investigators, combined their expertise in isotope studies, GIS and statistics, developing a new approach to identify the origin of pre-colonial Caribbean settlers.
DNA alone cannot tell us where someone came from
DNA studies are widely known methods for research on humans and human remains, but when it concerns geographic origins, these genetic studies are more informative about someone’s ancestors than about an individual’s actual (childhood) origin, explains Dr. Laffoon. Isotopes, in contrast, are increasingly applied to investigate origins in archaeological and forensic research, and have been highly successful at distinguishing between locally born people and immigrants. While we can identify which humans are not locals, such methods had not yet made much progress in identifying individual origins.
Developing new methods
In their research, the team combined isotope analyses of human teeth, with GIS (Geographic Information Systems), and statistical analysis to develop a new method to determine geographic origins of individuals. Through biochemical analyses of skeletal remains, we can use this method to provenance people from the past.
Highly accurate results
The team tested this new method on the tooth of a modern person of known origin from Caracas, Venezuela and the results showed a very good match with this location. Perhaps the most surprising aspect of this research is the high accuracy of the results obtained from the sample which happened to be the very first modern tooth that the research team tested the model with.
The team also tested the model on two archaeological teeth from different sites in the Caribbean of which the origin was suspected. While less precise than with the modern tooth, the results of these tests also indicated specific regions as the places of origin.
What makes this research particularly interesting, explains Dr. Laffoon, is that if it the method is further validated and the model is expanded spatially, it has the potential to vastly improve the accuracy and precision in these studies, so we can accurately identify someone’s origins, using relatively simple biochemical analyses. This would have very important implications not only for archaeological studies of migrations but also for forensic research into, for example, the identification of human remains in crime investigations.
J.E. Laffoon, T.F. Sonnemann, T. Shafie, C.L. Hofman, U. Brandes, and G.R. Davies. 2017. “Investigating human geographic origins using dual-isotope (87Sr/86Sr, δ18O) assignment approaches”. PLOS ONE, Vol. 12(2): 1-16.
Sampling: Andrzej Antczak and Marlena Antczak (modern tooth); Roberto Valcárcel Rojas and Marc Dorst (archaeological teeth).
Substantial progress in the application of multiple isotope analyses has greatly improved the ability to identify nonlocal individuals amongst archaeological populations over the past decades. More recently the development of large scale models of spatial isotopic variation (isoscapes) has contributed to improved geographic assignments of human and animal origins. Persistent challenges remain, however, in the accurate identification of individual geographic origins from skeletal isotope data in studies of human (and animal) migration and provenance. In an attempt to develop and test more standardized and quantitative approaches to geographic assignment of individual origins using isotopic data two methods, combining 87Sr/86Sr and δ18O isoscapes, are examined for the Circum-Caribbean region: 1) an Interval approach using a defined range of fixed isotopic variation per location; and 2) a Likelihood assignment approach using univariate and bivariate probability density functions. These two methods are tested with enamel isotope data from a modern sample of known origin from Caracas, Venezuela and further explored with two archaeological samples of unknown origin recovered from Cuba and Trinidad. The results emphasize both the potential and limitation of the different approaches. Validation tests on the known origin sample exclude most areas of the Circum-Caribbean region and correctly highlight Caracas as a possible place of origin with both approaches. The positive validation results clearly demonstrate the overall efficacy of a dual-isotope approach to geoprovenance. The accuracy and precision of geographic assignments may be further improved by better understanding of the relationships between environmental and biological isotope variation; continued development and refinement of relevant isoscapes; and the eventual incorporation of a broader array of isotope proxy data.
Go to Plos One to find the article.