Researchers had previously theorised that it was an increase in population that drove behavioural innovations which in turn led to the creation of these artefacts and eventually, the expansion out of Africa. However, by examining mollusc shells from Stone Age sites, Richard Klein of Stanford University and Teresa Steele of University of California, Davis, have determined that a significant population increase did not occur until the Later Stone Age (LSA), after the out of Africa migration had already begun... The researchers found that the median size of MSA shells was larger than that of LSA shells. This showed that selection...