On the Use of Biomineral Oxygen Isotope Data to Identify Human Migrants in the Archaeological Record: Intra-Sample Variation, Statistical Methods and Geographical Considerations

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.针对考古遗址骨骼遗骸的氧同位素分析（Oxygen isotope analysis），现已成为日益广泛应用于古人类迁徙研究的技术手段。该方法的核心假设为：人体化学组成会保留降水的δ¹⁸O比值，借此可有效识别迁徙个体，甚至推断其起源地。本研究作为首个全球性的此类调查，研究团队整合已发表的人类牙釉质与骨生物磷灰石同位素数据，旨在探究利用氧同位素分析识别考古记录中迁徙个体的有效性。我们通过人类δ¹⁸O比值数据发现，同一人群样本内的氧同位素数值存在显著差异。该差异可能源于两类因素：一是生理因素影响了原始同位素信号的保存；二是人类活动（如酿造、煮沸、炖煮、水源获取差异等）导致摄入水与食物的同位素数值发生变化。我们对比了不同统计方法识别出的异常值数量，发现识别迁徙个体的最优统计方法需依数据而定，但在多数考古场景下，四分位距（Interquartile Range, IQR）或中位数绝对偏差（median absolute deviation）更为适用。最后，通过对数据集的空间评估，我们发现欧洲不同地区的人类同位素数值存在大量重叠，因此截至目前，针对所分析的区域，仅依靠氧同位素分析无法精准确定个体的起源地。若使用得当，氧同位素分析可有效识别考古遗址中的第一代迁徙个体，但当样本量少于约25例时，难以通过统计方法判定迁徙个体。若缺乏当地既往的同位素分析数据，则应将每个样本视为独立数据集，可借助统计技术识别迁徙个体，但多数情况下不应尝试精准判定个体的具体起源地。