Abstract
Oxygen isotope analysis of archaeological skeletal remains is an increasingly popular tool to study past human migrations. It is based on the assumption that human body chemistry preserves the δ18O of precipitation in such a way as to be a useful technique for identifying migrants and, potentially, their homelands. In this study, the first such global survey, we draw on published human tooth enamel and bone bioapatite data to explore the validity of using oxygen isotope analyses to identify migrants in the archaeological record. We use human δ18O results to show that there are large variations in human oxygen isotope values within a population sample. This may relate to physiological factors influencing the preservation of the primary isotope signal, or due to human activities (such as brewing, boiling, stewing, differential access to water sources and so on) causing variation in ingested water and food isotope values. We compare the number of outliers identified using various statistical methods. We determine that the most appropriate method for identifying migrants is dependent on the data but is likely to be the IQR or median absolute deviation from the median under most archaeological circumstances. Finally, through a spatial assessment of the dataset, we show that the degree of overlap in human isotope values from different locations across Europe is such that identifying individuals’ homelands on the basis of oxygen isotope analysis alone is not possible for the regions analysed to date. Oxygen isotope analysis is a valid method for identifying first-generation migrants from an archaeological site when used appropriately, however it is difficult to identify migrants using statistical methods for a sample size of less than c. 25 individuals. In the absence of local previous analyses, each sample should be treated as an individual dataset and statistical techniques can be used to identify migrants, but in most cases pinpointing a specific homeland should not be attempted.
Highlights
Oxygen isotope analysis is an increasingly popular tool to study past human migrations, and has been applied to samples from many time periods and locations [1,2,3]
Full information about each specimen is recorded in the full dataset which has been deposited in the University of Cambridge data repository
Phosphate is considered to be less susceptible to diagenesis and an analytically preferable material to carbonate, the use of only phosphate analyses would have significantly restricted the sample size, given that there is a greater corpus of carbonate data than of phosphate
Summary
Oxygen isotope analysis is an increasingly popular tool to study past human migrations, and has been applied to samples from many time periods and locations [1,2,3]. The typical spread of biomineral isotope values in a population is an important factor to consider, difficult to test in a modern population We examine this assumption using data from the large number of archaeological studies published. Two factors are noteworthy—the oxygen isotope value of precipitation is strongly positively correlated with surface temperature at high latitudes and in tropical regions it is negatively correlated with the amount of rainfall [11] These factors cause temporal variations associated with past climatic changes in a given location, allowing oxygen isotopes to be used as a palaeoclimatic indicator but limiting the comparability of results for migration studies These factors cause temporal variations associated with past climatic changes in a given location, allowing oxygen isotopes to be used as a palaeoclimatic indicator but limiting the comparability of results for migration studies (e.g. [12, 13])
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