Kromdraai - Crouched in a shallow square grid dug into the red African earth, American graduate student Sarah Edlund uses a hand brush to scrape soil into a dustpan.She is uncovering scraping tools of a different kind - implements fashioned from quartz that were used 100 000 years ago to prepare animal hides."We have found a lot of quartz and this is important because it is not natural to this area ... It must have been brought here," Edlund said as she topped up her bucket with soil before taking it to a sifting device, where the dirt is separated from the quartz and other potential scientific treasures.The two-metre-by-two-metre grid was pegged out just a month ago, but the site - Swartkrans - has been excavated for decades, yielding hundreds of hominid fossils and shining a light on our evolutionary past stretching back almost 2 million years.The new ground being broken on a rocky hillside 25km northwest of Johannesburg helps to reveal the material culture of our ancestors a thousand millennia ago, shortly after they had evolved into our species, Homo sapiens."In this area we have what are mostly called scrapers, a certain form of stone tool," said Travis Pickering, a professor of anthropology at the University of Wisconsin.The reason behind this conjecture is simple: modern humans also scrape and prepare hides with similar tools. Clothing and perhaps shelter would have been the most likely end product of the hides.Much of the quartz retrieved at the site is in the form of flakes that may have come off while a tool was being fashioned.The scrapers themselves are fairly basic: a piece of quartz worked so that the edge can be used to literally scrape a hide from an animal.Specialisation siteBut what is striking is the sheer number unearthed, and what that suggests about our social development 100 000 years ago."There is a preponderance of them here, and what we think is this is perhaps a specialisation site, where they were working hides. And that is indicative of a very cognitively advanced sort of society," said Pickering, who directs the research project at Swartkrans.It also underscores the layered anthropological richness of the area, which includes the famed Sterkfontein caves across the valley, when it comes to the story of human evolution.Over 30 years ago, paleoanthropologist Bob Brain uncovered humanity's first use of fire here over a million years ago.Party to the discovery was the famed British travel writer Bruce Chatwin, who was fascinated by Brain's theory that humanity's evolutionary path was blazed by our attempts to avoid being eaten by predators.Recalling his discovery of burnt bones at the site, Brain, now a spritely 84, told Reuters that the use of fire "was an attempt to evade the constant danger at night of the predators just waiting for their meals."This story has slowly come out of this excavation, which I was involved with for 50 years," he said.