Significance Paleogenetic and isotope data from human remains shed new light on residential rules revealing patrilocality and high female mobility in European prehistory. We show the crucial role of this institution and its impact on the transformation of population compositions over several hundred years. Evidence for an epoch-transgressing maternal relationship between two individuals demonstrates long-debated population continuity from the central European Neolithic to the Bronze Age. We demonstrate that a simple notion of “migration” cannot explain the complex human mobility of third millennium BCE societies in Eurasia. On the contrary, it appears that part of what archaeologists understand as migration is the result of large-scale institutionalized and possibly sex- and age-related individual mobility.

Abstract Human mobility has been vigorously debated as a key factor for the spread of bronze technology and profound changes in burial practices as well as material culture in central Europe at the transition from the Neolithic to the Bronze Age. However, the relevance of individual residential changes and their importance among specific age and sex groups are still poorly understood. Here, we present ancient DNA analysis, stable isotope data of oxygen, and radiogenic isotope ratios of strontium for 84 radiocarbon-dated skeletons from seven archaeological sites of the Late Neolithic Bell Beaker Complex and the Early Bronze Age from the Lech River valley in southern Bavaria, Germany. Complete mitochondrial genomes documented a diversification of maternal lineages over time. The isotope ratios disclosed the majority of the females to be nonlocal, while this is the case for only a few males and subadults. Most nonlocal females arrived in the study area as adults, but we do not detect their offspring among the sampled individuals. The striking patterns of patrilocality and female exogamy prevailed over at least 800 y between about 2500 and 1700 BC. The persisting residential rules and even a direct kinship relation across the transition from the Neolithic to the Bronze Age add to the archaeological evidence of continuing traditions from the Bell Beaker Complex to the Early Bronze Age. The results also attest to female mobility as a driving force for regional and supraregional communication and exchange at the dawn of the European metal ages.

Human mobility, ranging from individual residential changes to large-scale population replacements, was crucial for societal transformations. While for decades population change or stability was inferred from relics of material culture and burial customs, recent analytical developments have disclosed direct evidence from ancient human skeletal remains. Radiogenic and stable isotope analysis—particularly of strontium (Sr) and oxygen (O) bound in the hydroxyapatite of tooth enamel—has identified first-generation nonlocal individuals (1, 2), and ancient mitochondrial (3) and nuclear DNA data (4, 5) have revealed population continuity and abrupt or gradual replacements.

Archeologists have vigorously debated population continuity and replacements during the transition from the Neolithic to the Bronze Age in central Europe in the late third millennium BC (6⇓–8). South of the Danube, three archaeological cultural entities are commonly recognized: the Corded Ware Complex (CWC; 2800–2500/2200 BC), the Bell Beaker Complex (BBC; 2500–2150 BC), and the Early Bronze Age (EBA; 2150–1700/1650 BC). Genome-wide analyses demonstrated that burials of the central European CWC traced up to 75% of their ancestry to populations related to those living in the north Pontic steppes archaeologically classified as the Yamnaya Culture (4, 5). The exact reasons for the expansion of steppe pastoralists to the west and east are currently unknown. Recent studies, however, suggest that a possible pandemic might have triggered this process by spreading a close relative of Yersinia pestis, the causative agent of bubonic plague (9, 10). On a smaller geographical scale, stable isotope data exhibited the crucial role of individual mobility, often connected with females (11, 12).

This paper focuses on the transition from the BBC to the EBA. Archeological evidence of the BBC includes burials with distinct bell-shaped ceramic cups, archery equipment, and occasionally gold, amber, and bronze objects (13, 14). Causes for its pan-European distribution from the Iberian Peninsula to the Carpathian Basin may have included human mobility, increasing transregional connectivity, or social differentiation accompanied by widely recognized symbols of prestige or status (15, 16). Consequently, the BBC was subject to one of the earliest large-scale Sr isotope studies (17, 18). It revealed multidirectional residential moves, which were related to subsistence practices rather than to actual mass migrations (19⇓–21). In the subsequent EBA, human mobility was essential to distribute copper and tin ores, which do not occur together, as well as finished artifacts (22). Isotope analyses in EBA contexts revealed a heterogenic picture ranging from no clear indication for nonlocal individuals at Singen in southwest Germany (23) to a few nonlocal persons in mostly smaller burial communities in central Germany (24), while data from Únětice contexts in Silesia (Poland), were interpreted to be a reflection of “hypermobility” (25).

All this research illuminates the complex dynamics of social change and human mobility at the transition from the end of the Neolithic BBC to the EBA. To comprehend the mechanisms behind them it is crucial to investigate the spatial and quantitative scale of mobility as well as its relatedness to kinship, gender, and age. A suitable region to study this is the Lech River valley south of Augsburg (Bavaria, Germany) (Fig. 1 and SI Appendix, Fig. S1), where excavations over the last 20 y have unearthed almost 400 burials of both archaeological complexes and several associated EBA settlements, and radiocarbon dating of the human remains revealed a chronological continuum from the BBC to the EBA (26).

Fig. 1. Investigated BBC and EBA cemeteries in the Lech River valley. All sites are located along a loess ridge and share similar environmental conditions. Produced using Copernicus data and information funded by the European Union—EU-DEM layers; Geology 1:200.000. Data copyright Bundesanstalt für Geowissenschaften und Rohstoffe (BGR). (Graphic: S. E. Metz.)

Here we present genetic sex assignments and ancient mitochondrial DNA analyses as well as 87Sr/86Sr and δ18O data for 84 human individuals from seven sites in the Lech River valley (Fig. 1 and Dataset S1, Table 1). The DNA analyses aimed at revealing direct maternal lineages connecting individuals from the same and different cemeteries, as well as between representatives of the BBC and EBA. The isotope analyses targeted the identification of first-generation nonlocals. The 87Sr/86Sr ratios in human tooth enamel depend on the geological conditions of the area from which foodstuffs were exploited during tooth formation in early life, while δ18O values relate to temperature, elevation, and distance from the sea (1, 2) (SI Appendix, Text S1). All samples were recovered from a small area of ∼10 km north–south and maximally 6 km east–west, which ensures well-comparable geologic and climatic conditions. The samples include 19 representatives of the BBC and 65 of the EBA of various age groups and both sexes. Fourteen faunal enamel samples helped to estimate the Sr isotope baseline.

Conclusion Interdisciplinary research combining archeological, Sr and O isotope, and mtDNA analyses disclosed striking evidence for patrilocal residential rules and female exogamy persisting over at least 800 y in central Europe from about 2500 to 1700 BC, and possibly starting even earlier in the CWC (12). On the one hand, the archeological record, radiocarbon dates, burial practices, mtDNA haplogroups, and isotope data—especially of male and subadult individuals—support settlement continuity from the Late Neolithic BBC to the EBA. This includes indication of direct maternal kinship between a male with BBC and a female with EBA attributes. On the other hand, numerous nonlocal Sr isotope ratios among the females and the diversification of the maternal lineages point to exogamy and female mobility as a driving force of regional and supraregional communication and knowledge transmission in a time of major innovations. Systematic individual movements are an important factor in third millennium BCE societies in Eurasia and force us to reexamine evidence of “migration” that may actually be the result of large-scale institutionalized and possibly sex- and age-related individual mobility.

Materials and Methods Archaeological Background. Since the 1980s, excavations in the Lech River valley south of the city of Augsburg (Bavaria, Germany; Fig. 1 and SI Appendix, Fig. S1) have unearthed cemeteries of the Late Neolithic BBC and the Early and Middle Bronze Age, some of them covering multiple periods. Some of the EBA sites are associated with a hamlet. Cultural attribution is based on archaeological criteria such as grave goods. Direct radiocarbon dating of the human remains revealed age ranges of 2500–2150 cal BC for the BBC burials and 2150–1650/1600 cal BC for the EBA burials (26). Eighty-four sampled individuals derive from seven cemeteries and include all burials of combined BBC and EBA sites and a selection from larger EBA cemeteries based on chronologically significant or remarkable grave goods and a representative number of children and adults of both sexes (Dataset S1, Tables 1 and 2). Ancient DNA Analysis. Teeth were sampled in clean room facilities at the University of Tübingen by sawing them apart transversally at the border of crown and root and removing dentine from inside the crown with a sterile dentistry drill. Extraction was performed following an established protocol (45), and an aliquot of extract was used to generate double-indexed libraries (46, 47) that were sequenced before and after enrichment for mtDNA (48) on a NextSeq with 2 × 101+8+8 and a HiSeq2500 with 2 × 101+8+8 cycles. Negative controls were included in the extraction and library preparation and taken along for all further processing steps (Dataset S1, Table 9). Base call files produced by the instrument’s software were converted to raw sequences that were demultiplexed according to the index combinations they received during library preparation. A software pipeline was used (49) to clip adapter sequences, map reads to the reference—hg19 for shotgun data and revised Cambridge reference sequence (rCRS) for mitochondrial capture data—using Burrows–Wheeler Aligner (BWA) (50) with parameters “-l 10000 -n 0.01,” and to remove duplicate reads. Mitochondrial consensus sequences were called while jointly estimating the rate of deamination damage and contamination from present-day human sources with the probabilistic iterative method applied in the software schmutzi (29) using the accompanying tool log2fasta with parameter -q 20. Poly-C regions and mutational hotspots at positions 303–315, 515–522, and 16519 were masked. Sex was assigned on the basis of the shotgun-sequencing data (51), restricted to reads that showed postmortem damage with the script pmdtools (52), parameter “–threshold 3.” Mitochondrial haplogroups were assigned manually by consulting the output of Haplofind (53) and Haplogrep2.0 (54). Haplogroup frequencies and F st analysis were conducted on a conservative dataset, counting only once a shared haplotype that occurred within a multiple burial or between very closely located burials. Pairwise F st comparisons against other ancient populations (3) were performed with Arlequin ver3.5.2 (55) using the Tamura & Nei substitution model and gamma value 0.300 on the HVS-I region (16126–16369), excluding the poly-C-stretch at 16184–16195. The significance level was corrected for using the Benjamini–Hochberg correction to limit false positives (56). To assess if the different haplogroup frequencies seen in BBC and EBA can be attributed to genetic drift alone, the Test for Population Continuity (3) was applied. All mtDNA sequences generated in this study are deposited in GenBank (accession numbers: MF498658—MF498737). Strontium and Oxygen Isotope Analyses. Sr and O isotope analyses on enamel samples were carried out at the Curt Engelhorn Centre for Archaeometry in Mannheim and the Department for Applied and Analytical Paleontology at the University of Mainz, Germany, following previously described methods (57, 58) (for comparison, see SI Appendix, Text S1). Statistical analysis was carried out using WinSTAT for Excel 2007.1 and Sigma Plot. All datasets used in Student’s t tests were tested for normality using the Kolmogorov–Smirnov test.

Acknowledgments The authors are grateful to M. Hermann and S. Gairhos (Stadtarchäologie Augsburg), H. Dietrich (Landesamt für Denkmalpflege, Bayern), and R. Linke (Arbeitskreis für Vor- und Frühgeschichte, Augsburg Süd) for access to the skeletons; to E. Nelson for anthropological age and sex determinations; to G. Borngässer, M. Gottschalk, S. Klaus, B. Höppner, and S. Pagacs (Curt Engelhorn Center for Archaeometry Mannheim) for sample preparation and isotope analysis; to F. Göhringer for photography and 3D scanning; and to J. Peters, M. Harbeck, W. Haak, A. Peltzer, M. Spyrou, and C. Posth for suggestions and discussions. Comments by anonymous reviewers and the editor, as well as language editing by Anne Gibson, improved the manuscript. Financial support by the Heidelberg Academy of Sciences (project “Times of Upheaval: Changes of Society and Landscape at the Beginning of the Bronze Age”), by the German Research Foundation [KR 4015/1-1 (to J.K. and A.M.)], and by the Crocallis–Stiftung (to A.S.) is highly acknowledged.