Between these extremes is the view – currently supported by archaeologists Chris Henshilwood, Curtis Marean, Ian Watts and others – that there was indeed some kind of 'human revolution' but that it occurred in Africa and spanned tens of thousands of years. The term "revolution" in this context would mean not a sudden mutation but a historical development along the lines of "the industrial revolution" or "the Neolithic revolution". In other words, it was a relatively accelerated process, too rapid for ordinary Darwinian "descent with modification" yet too gradual to be attributed to a single genetic or other sudden event. These archaeologists point in particular to the relatively explosive emergence of ochre crayons and shell necklaces apparently used for cosmetic purposes. These archaeologists see symbolic organisation of human social life as the key transition in modern human evolution. Recently discovered at sites such as Blombos Cave and Pinnacle Point, South Africa, pierced shells, pigments and other striking signs of personal ornamentation have been dated within a time-window of 70,000–160,000 years ago in the African Middle Stone Age, suggesting that the emergence of "Homo sapiens" coincided, after all, with the transition to modern cognition and behaviour. While viewing the emergence of language as a 'revolutionary' development, this school of thought generally attributes it to cumulative social, cognitive and cultural evolutionary processes as opposed to a single genetic mutation.