Revisiting the Past: How Social Change Drove Declines in Male Population Thousands of Years Ago

In a recent study, researchers from the French research team at CNRS, MNHN, and Paris Cité University have suggested that the decline in the male population worldwide thousands of years ago may have been more due to social change than an unprecedented wave of violence. The team proposes that this decline occurred as societies transitioned from diverse reproductive systems to ones based on patrilineal lines, where men are aligned based on their fathers’ clans.

During the end of the Neolithic period, between 3,000 and 5,000 years ago, societies made this shift, resulting in a significant decrease in Y chromosome diversity responsible for male sexual characteristics. A study in 2015 revealed a collapse of male genetic diversity about 5,000 years ago, with one man for every 17 women involved in reproduction in Europe. However, this 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 a change in social organization as 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.

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.

The study raises questions about how cultural changes can impact human evolution and genetic diversity over time. It also highlights the importance of understanding historical shifts to better understand modern-day genetic differences between individuals and populations.

In conclusion, while previous theories have focused on violence as the main driver behind declines in male population numbers worldwide thousands of years ago, new research suggests that social change may have played a more significant role. By studying past transitions from diverse reproductive systems to patrilineal ones based on clans’ power or resources within specific populations and regions worldwide can shed light on how cultural changes affect genetic diversity and evolutionary patterns over time.