Biological distance at the Ryan Mound site

Area of Science:

• Bioarchaeology
• Physical Anthropology
• Skeletal Biology

Background:

• The Ryan Mound site in California has been extensively studied, with an assumption of biological continuity over its 2000-year span.
• Previous research has not empirically tested the biological continuity of the adult population at Ryan Mound across different time periods.

Purpose of the Study:

• To determine if adults at the Ryan Mound represented a biologically continuous population across three distinct temporal periods.
• To investigate potential population changes and movements within the Ryan Mound's archaeological context.

Main Methods:

• Scored 38 nonmetric cranial and 4 post-cranial skeletal traits on adult individuals.
• Utilized chi-square and Fisher's exact tests for trait correlations, and converted data to binary values for Mean Measure of Divergence (MMD) analysis.
• Applied standardized MMD statistical analyses to assess biological differences between temporal groups.

Main Results:

• After data reduction to 36 traits, standardized MMD analyses indicated significant biological differences between individuals from the oldest and most recent temporal periods.
• The findings challenge the assumption of a single, continuous population throughout the Ryan Mound's occupation.

Conclusions:

• Nonmetric skeletal trait analysis is crucial for testing biological continuity in archaeological populations.
• The results suggest that new populations may have migrated into the Ryan Mound region, potentially during the Meganos intrusion or between AD 1500 and AD 1800.
• Comparative data from adjacent sites support the theory of population replacement or significant admixture, as indicated by the Meganos intrusion.