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Archaeological shellfish size and later human evolution in Africa.
Richard G Klein1, Teresa E Steele
1Department of Biology, Stanford University, Stanford, CA 94305, USA.
Summary
Early human expansion from Africa (Middle Stone Age) showed no signs of population growth, contrary to previous assumptions linking behavioral changes to increased populations. Archaeological evidence suggests small, stable populations during this period.
Area of Science:
- Archaeology
- Paleoanthropology
- Human Evolution
Background:
- The African Middle Stone Age (MSA) (~200-50 ka) is investigated for the origins of behavioral modernity preceding the global expansion of modern humans.
- Potential early art objects like incised ocher and shell beads from MSA sites suggest cognitive modernity.
Observation:
- Archaeologists often link the emergence of art and behavioral changes to population growth.
- Gastropod shell size in coastal middens can indicate collection intensity, reflecting population size.
Findings:
- Economically important Cape turban shells and limpets from South African MSA layers are significantly larger than those from later Later Stone Age (LSA) layers under similar environmental conditions.
- Larger shell size in MSA sites suggests less intense collection, implying smaller, stable human populations.
Implications:
- Cognitive modernity during the MSA was not driven by population growth.
- Significant human population increase occurred later, near the MSA/LSA transition, coinciding with the Out-of-Africa expansion.
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