Insights into the cognitive evolution of genus Homo: Eye-tracking analysis of stone tool recognition in trained versus novice modern humans

• Tool opacity suggests early technologies required transmission to persist. • Recognition does not generalize to unfamiliar tools without deeper knowledge. • Even basic stone tools challenge naive perception without guidance. Eye tracking technologies have recently been used to analyze the visual exploration of stone tool stimuli by modern humans to investigate the cognition of our ancestors. As a tooling species, modern humans show remarkable abilities when it comes to understanding and manipulating complex tools, such as a microscope. Nevertheless, our earliest technological steps, at least the first ones for which we have archaeological evidence, were stone tools, which today might appear easier to grasp than a highly sophisticated surgical telemanipulator. However, the complexity and diversity of lithic industries require a certain level of knowledge to be fully understood. Thus, the question remains whether modern humans can truly extract relevant features from stone tools to distinguish them, for example, from stones fractured by uncontrolled percussion (broken stones), which might look like the first lithic industries. Naive participants, divided into two groups with one receiving a training about stone tool features and the other not, were asked to distinguish stone tools from broken stones. Results show that participants needed a minimal level of knowledge to distinguish choppers or handaxes from broken stones. Nevertheless, trained participants were still not able to correctly classify unknown types of stone tools as tools, suggesting that they needed deeper knowledge to transfer their skills. Our findings underline the important role of technical knowledge in our ancestors’ expertise in stone knapping.