Neolithic Male Population Decline in Europe Linked to Social Change, Study Suggests

A recent archaeological study proposes that the dramatic decline in male effective population sizes observed worldwide between 3,000 and 5,000 years ago may have been caused by the rise of patrilineal social systems in the Neolithic period, rather than violent clashes between different clans as previously hypothesized. The study, which analyzed anthropological field data from contemporary non-belligerent patrilineal groups and modeled different socio-demographic scenarios, suggests that ancient changes in social structures connected to global changes in subsistence systems could explain the reported decline in Y chromosome diversity.

Previous genetic studies had found a pronounced decline in male effective population sizes worldwide around 3000-5000 years ago, while female effective population sizes continued to increase over time. This pattern was initially interpreted as the result of violent competition between patrilineal groups, leading to the extinction of certain groups and a reduction in male effective population size. However, the new study challenges this "violence hypothesis" and proposes a peaceful explanation involving the splitting of clans into different subclans (lineal fission) and differences in social status that led to the expansion of certain lineages at the expense of others.

Why this matters: The findings provide new insights into human social organization during the Neolithic and Bronze Age periods, challenging previous assumptions about the causes of genetic bottlenecks in male populations. Understanding the complex interplay between social structures, subsistence systems, and genetic diversity can shed light on the evolutionary history of human populations and the factors that have shaped our species' development over time.

The researchers found that two key processes played an important role in genetic diversity: the splitting of clans into different subclans and differences in social status that led to the expansion of certain lineages at the expense of others. According to the study, a segmentary patrilineal system, where variance in reproductive success between patrilineal groups and lineal fission can lead to a substantial reduction in the male effective population size without resorting to violence, may be sufficient to explain the reported decline in Y chromosome diversity.

The estimated timeframe of this bottleneck varies between world regions, ranging from 8300 BP in the Near East to 1400 BP in Siberia, and was estimated to be around 5000 BP in Europe. The study suggests that a peaceful explanation involving ancient changes in social structures linked to global changes in subsistence systems may be more plausible than the previously proposed violence hypothesis.

The multidisciplinary research team, led by scientists at the Max Planck Institute for Evolutionary Anthropology, analyzed ancient DNA data from four fully excavated Avar period cemeteries in Europe's Carpathian Basin, dating back to the 6th-9th centuries CE. The study revealed that the Avar communities practiced a strict patrilineal system of descent, with women playing a key role in promoting social cohesion by marrying outside their original community. The researchers were able to reconstruct extensive pedigrees spanning up to nine generations, showing that these communities maintained a detailed memory of their ancestry and knew their biological relatives over historical context.

Key Takeaways

• Decline in male effective population sizes 3,000-5,000 years ago linked to patrilineal systems
• Peaceful explanation: clan splitting, status differences led to lineage expansion, not violence
• Estimated bottleneck timeframe varies globally, around 5,000 BP in Europe
• Avar communities practiced strict patrilineal descent, women married outside their community
• Detailed ancestral memory and biological relatedness maintained over historical context