Y-Chromosome Decline in Human Populations: A Social Change Rather than Violence

In recent years, a French research team from CNRS, MNHN, and Paris Cité University has shed new light on the notable decline in the male population thousands of years ago worldwide. The study suggests that this decline was not due to an unprecedented wave of violence but rather a social change that occurred as societies transitioned from diverse reproductive systems to ones based on patrilineal lines.

According to the researchers, this shift took place at the end of the Neolithic period, between 3,000 and 5,000 years ago. During this time, clans with lower reproductive capacity impacted their entire lineage. This decline in Y chromosome diversity was only recently identified through analysis of current men’s Y chromosomes. A study in 2015 revealed that one man for every 17 women was involved in reproduction in Europe at that time.

The decline was particularly severe in Europe but also affected regions like the Near East, Siberia, and Africa over a broader timeframe. Contradicting previous theories of violent clan warfare leading to the loss of Y chromosome diversity, the new study suggests that a change in social organization was the cause. This shift from a hunter-gatherer lifestyle to agro-pastoralism favored patrilineal systems, where clans with more power or resources were more successful in reproduction.

To understand this social transition better, the team collected over a thousand genomes from patrilineal populations and demonstrated significant loss of Y chromosome diversity in segmental patrilineal systems. They attribute this social transition to the rise of agro-pastoral economies, which favored patrilocality and patrilineality. Future research aims to explore these patterns across different continents to provide region-specific insights into this historical shift.

Overall, this study provides compelling evidence that societal changes rather than violence played a significant role in shaping human populations throughout history. Understanding these historical shifts can help us better understand our past and inform our future decisions about how we organize society today.