Pax Augusta
Elite member
Genomic transformation and social organization during the Copper Age–Bronze Age transition in southern Iberia
SCIENCE ADVANCES • 17 Nov 2021• Vol 7, Issue 47 • DOI: 10.1126/sciadv.abi7038
Abstract
The emerging Bronze Age (BA) of southeastern Iberia saw marked social changes. Late Copper Age (CA) settlements were abandoned in favor of hilltop sites, and collective graves were largely replaced by single or double burials with often distinctive grave goods indirectly reflecting a hierarchical social organization, as exemplified by the BA El Argar group. We explored this transition from a genomic viewpoint by tripling the amount of data available for this period. Concomitant with the rise of El Argar starting ~2200 cal BCE, we observe a complete turnover of Y-chromosome lineages along with the arrival of steppe-related ancestry. This pattern is consistent with a founder effect in male lineages, supported by our finding that males shared more relatives at sites than females. However, simple two-source models do not find support in some El Argar groups, suggesting additional genetic contributions from the Mediterranean that could predate the BA.
DISCUSSION
Abstract
The emerging Bronze Age (BA) of southeastern Iberia saw marked social changes. Late Copper Age (CA) settlements were abandoned in favor of hilltop sites, and collective graves were largely replaced by single or double burials with often distinctive grave goods indirectly reflecting a hierarchical social organization, as exemplified by the BA El Argar group. We explored this transition from a genomic viewpoint by tripling the amount of data available for this period. Concomitant with the rise of El Argar starting ~2200 cal BCE, we observe a complete turnover of Y-chromosome lineages along with the arrival of steppe-related ancestry. This pattern is consistent with a founder effect in male lineages, supported by our finding that males shared more relatives at sites than females. However, simple two-source models do not find support in some El Argar groups, suggesting additional genetic contributions from the Mediterranean that could predate the BA.
DISCUSSION
Our focused study on the southeastern part of Iberia highlights the potential of genetic analysis on a regional level in the light of broader-scale population dynamics in Europe. Overall, we were able to show that the structure of CA populations shows persistent genetic stability and continuity since the Neolithic. This is coupled with a differential HG ancestry in the South in addition to potential early contact between southeastern Iberian CA and Mediterranean populations, which is also revealed by numerous threads of archaeological evidence (13–17). We provide nuanced evidence for the arrival of steppe-related ancestry in southeastern Iberia by 2200 cal BCE, when widespread social and cultural changes occurred across much of southern Iberia, including the end of the ditched enclosures system of population aggregation and the emergence of BA groups. In the Southeast, all sampled BA groups can be shown to carry steppe-related ancestry, while the more extensively sampled El Argar groups also carry excess Iran_N-like ancestry, which has also been observed in other CA and BA Mediterranean groups. The analysis of one outlier from El Argar reveals a central Mediterranean migrant individual with additional North African ancestry. Overall, we propose that El Argar has likely formed from a mixture of new groups arriving from north-central Iberia, which already carried central European steppe-related ancestry (and the predominant Y-chromosome lineage) and local southeastern Iberian CA groups that differed from other regions in Iberian in that they carried excess Iran_N-like ancestry similar to eastern and/or central Mediterranean groups. Moreover, the large sample sizes of early and late El Argar groups show that the Iran_N-like ancestry contribution in the local CA stratum was not enough to explain this type of ancestry satisfyingly, which, in turn, argues for a continued connection to and genetic influence from the Mediterranean BA at least until the end of the El Argar period. Last, we were able to shed light onto the population structure of Early Bronze El Argar societies at the intrasite level. In La Almoloya, a closer genetic relationship among males is a strong indicator of patrilineality.