The Still Bay culture was one of the most advanced Middle Stone Age groups in Africa when it emerged some 78,000 years ago. Archaeologist Chris Henshilwood's excavations at Blombos Cave on the Southern Cape of South Africa have revealed distinctive tools, including carefully worked stone points and bits of rock inscribed with apparently symbolic designs. But evidence of the technology disappears abruptly about 71,000 years ago, along with all proof of human habitation in southern Africa. It would be 7,000 years before a new culture appeared, with a markedly different toolkit, including crescent-shaped blades probably used as arrowheads.
     These and other findings have challenged the once-dominant idea that human culture - as exemplified by art such as carvings and jewellery - appeared in an explosive transformation during the Late Stone Age, some 40,000 to 50,000 years ago, in north Africa and Europe. Blombos and other sites suggest a more gradual cultural and technological development, beginning far earlier, during the Mesolithic throughout Africa.
     Henshilwood is beginning excavations on a site called Klipdrift Shelter, west of Blombos, that could allow him to look at the rise of Still Bay's successor - the Howiesons Poort culture, which appeared 65,000 years ago and persisted for about 5,000 years.
     At about the time the Still Bay culture disappeared, the planet - already in the middle of a glacial period - began to cool even further, causing sea levels to fall. Genetic data suggest that the entire population of modern humans contracted at around the same time, then rebounded and expanded in Africa and onto other continents.
     Multiple teams are now racing to determine the part climate might have played in driving human evolution during this period. The data will allow a team at the CNRS (National Centre for Scientific Research), in Bordeaux, France, to build a high-resolution model of climate in Europe and southern Africa, beginning with the time spanning the Still Bay and Howiesons Poort cultures.
     Alison Brooks, director of the Center for the Advanced Study of Hominid Paleo-biology at the George Washington University in Washington, D.C., is co-authoring a forthcoming publication that aligns palaeo-climate data with archaeological data throughout Africa, and says that each region of the continent seems to have has its own story. "There's a lot of complexity here," she says.

Edited from Nature (15 February 2012)