Quantitative analysis of the symmetry of artefacts: Lower Paleolithic handaxes

The ability to perceive and produce symmetrical shapes is usually taken to be a major step in the development of human cognition. Despite the importance of the concept of symmetry to studies of early human development, its current use is usually based on loose qualitative assessment. A more informative approach would be to use a continuous scale of this shape property rather than the strict current language of "more" or "less". A symmetry measurement tool has been developed, which is based on evaluation of the minimal distances that the vertices of a structure have to move in order to attain the required symmetry. Using this Continuous Symmetry Measure (CSM) method, it is possible to evaluate quantitatively how much symmetry exists in a non-symmetrical configuration and how the nearest symmetrical shape looks. We test and demonstrate the feasibility and versatility of this approach on handaxe samples from three Lower Paleolithic sites in Israel, Ubeidiya, Gesher Benot Ya'aqov and Ma'ayan Barukh, representing various stages in the Acheulian Techno-complex of the Levant. We provide, to the best of our knowledge for the first time, quantitative demonstration that the overall symmetry of handaxes generally increases, and that the variability decreases over time.