Unearthing the Causes of Declining Male Populations: A Study Challenges Previous Assumptions and Reveals the Impact of Social Change on Y Chromosome Diversity

A recent study by a French research team from CNRS, MNHN, and Paris Cité University sheds new light on the decline in the male population worldwide thousands of years ago. The team posits that this decline may have been more due to social change than an unprecedented wave of violence.

The study took place at the end of the Neolithic period, between 3,000 and 5,000 years ago, resulting in a significant decrease in Y chromosome diversity. This decline 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 during this time.

The decline was particularly severe in Europe but also affected regions like the Near East, Siberia, and Africa over a broader timeframe. However, 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 primary 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.

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 that 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 challenges previous assumptions about the causes of declining male populations and provides valuable insights into how social changes can shape genetic diversity over time.