Shells show rise of Homo sapiens

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The size of ancient limpet shells suggests that human populations began swelling around 50,000 years ago, long after key cultural innovations appear in the archaeological record.

Teresa Steele at the University of California, Davis, and Richard Klein at Stanford University, California, measured the size of limpet shells from archaeological sites in South Africa, inferring that smaller shells are linked to increased harvesting and therefore larger human settlements. Shells from the Middle Stone Age, 200,000 to 50,000 years ago, were consistently bigger than shells from Late Stone Age sites, suggesting that there was an increase in population growth in this later era.

Humans living on the coast of South Africa began creating symbolic artefacts, such as shell beads, around 100,000 years ago, when populations are thought to have been smaller. The researchers say their findings challenge the theory that such cultural behaviour was catalysed by high population densities that helped new innovations to spread.

Proc. Natl Acad. Sci. USA (2013)

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