A 2014 study published in the journalScience discovered Levallois and bifacialstone tools in an archaeological site near Nor Geghi. The artifacts, found preserved in soil under a later lava flow and dated at 325,000 – 335,000 years old, were a mix of two distinct stone tooltechnology traditions: bifacial tools and Levallois tools. Daniel Adler suggests that the coexistence of bifacial and Levallois tools at the site provides the first clear evidence that local populations developed Levallois technology out of existing bifacial technology and that the artifacts found at Nor Geghi reflect the technological flexibility and variability of a single population. He further concludes that this challenges the view that technological change resulted from population change and suggests instead that Levallois technology developed independently from existing technology within different human populations who shared a common technological ancestry.