Sex-specific processes in European prehistory and beyond
: Y chromosome, mitochondrial DNA and genome-wide variation

  • Pierre Justeau

Student thesis: Doctoral Thesis


The spread of the Neolithic way of life diffused from Anatolia to Western Europe through two major routes: the continental one alongside the Danube River, and the Mediterranean route. Genomic analysis showed the existence of several patterns of admixture between the European hunter-gatherers and the incoming Neolithic farmers in accordance with both routes of expansion. However, little is known about the residence rules associated with the expansion of the Neolithic farmers. The most common residential rules across the world are characterized by patrilocality and matrilocality, where couples migrate to their husband’s or wife’s residence respectively. Less common is a neolocal system which describes when both spouses migrate to a new place of residence while a multilocal system depicts when both spouses switch between several places of residence. To characterize such migratory events associated to the neolithization of Western Europe, I developed a method using a custom pipeline written in Python based on graph theory, to collect and compare mitochondrial and Y-chromosome genetic data for 400 Neolithic samples from the Near East to Western Europe with emphasis on France and the British Isles. My final aim was to build a network where each node is a sample and the links between them display their maternal and/or paternal relationship. By using the Louvain algorithm for communities detection, I created clusters (graph communities) based on the relatedness of their mitochondrial and Y-chromosome inheritance to graphically describe the social structure within and between these communities (e.g., matrilocal, patrilocal, neolocal, multilocal system). By exporting the network on a map, I demonstrated the existence of a co-migration of males and females from the Near East westwards to Europe. This neolocal system of expansion is replaced by other residences rules when the incoming farmers reach the Western fringe of continental Europe. Then, the introduction of the mitochondrial DNA haplogroups in the British Isles follows two different processes of dispersal not yet reported. Firstly, the assimilation of some mitochondrial haplogroups into the male Y chromosome clade I2a from France prior migrating to the British Isles, and secondly, the dispersal of females without assimilation to any male clade, referring to a patrilocal residence rule.
This patrilocal system associated to female exogamy is a residence rule that persisted in some European regions at least until the Bronze Age. The emergence of Bronze Age society in North Western Europe is linked with the expansion of the Bell Beaker culture around 2750 BC. This migration brought into Western Europe a genetic ancestry from the Eurasian steppe which was absent during the Neolithic. Moreover, the appearance of the Y-chromosome R1b-M269 which reached 90% of the Y lineages in the British Isles by replacing the male Neolithic lineage I2a reinforces the existence of an important genetic turnover associated with the appearance of the Bronze Age society. However, I demonstrated a more contrasting story by using a modified version of the pathPhynder software augmented with pairwise comparison between the ancient samples. I analysed nine Bronze Age samples from the Links of Noltland in Orkney generated by the Dr Katharina Dulias from the University of Huddersfield, alongside nine Irish, 17 English, 23 Scottish and four Swedish Y-chromosome Neolithic samples published in the literature. The persistence of the male Neolithic lineage I2a in the Bronze Age Links of Noltland samples alongside the Y-chromosome lineage R1b-M269 suggests the existence of a patrilocal system associated with the migration of Bronze Age females from continental Europe indicating of an exogamic system.
After the Bronze Age, Western Europe experienced other migratory events during the Iron Age, the expansion of the Roman Empire, and the Angle-Saxon and Frankish conquest in Belgium, France, and England during the fifth century AD. To investigate the impact of Angle, Saxon, and Frankish migrations in the evolution of the genetic makeup of the Merovingian dynasty (in France and Belgium), I analysed six ancient genomes-wide samples assigned to the proto-Merovingian (n=2) and Merovingian (n=2) cultures and two French samples from the High/Late Middle Age. The results potentially suggested a first migration from Germany/Denmark to Northern France seen through the proto-Merovingian samples. A
second migration can be traced through one Merovingian sample from Belgium, which is closer to the Early Medieval samples from Germany/Denmark. However, the proximity of one of the Merovingian samples from France and the High/Late Medieval samples to the two French
proto-Merovingian samples suggests that the potential first migration was durable, and not
replaced by subsequent migrations, like the Viking conquest for example.
Date of Award22 Nov 2022
Original languageEnglish
SupervisorMartin Richards (Main Supervisor), Maria Pala (Co-Supervisor) & Ceiridwen Edwards (Co-Supervisor)

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