Yes- and No-Gestures Explained by Symmetry

In most cultures, “yes” is indicate by a vertical head movement (nod), while “no” is indicated by a left-right movement (shake). In this paper, we show that basic symmetries can explain this cultural phenomenon. 1 Formulation of the Problem In most cultures, “yes” is indicated by a vertical head movement (nod), while “no” is indicated by a left-right movement (shake); see, e.g., [1]. There are a few exceptions to this rule: e.g., in Bulgaria, the gestures are swapped, but in most cultures, “yes” and “no” are described by similar gestures. Why? 2 Our Explanation: General Idea One of the main purposes of communications is to coordinate efforts between different people. From this viewpoint, “yes” means agreement; it means, in general, that we can safely continue what we have agreed on or what has been proposed. In contrast, “no” means disagreement, it means a change in plans. In view of this, it is more crucial not to miss the “no” gesture; indeed: • if we miss the “yes” gesture, we will either continue our previous action (as intended), or continue waiting for an agreement, which is probably also OK in situations where we have already been waiting for such agreement for some time; • however, if we miss the “no” gesture, we will erroneously continue the action that needs to be stopped – and consequences may be serious: e.g., a primitive person during the ancient hunt may fall into a pit or not notice a wild animal attacking him. So, we expect that between two possible gestures, the most easily detectable one will correspond to “no”, while the less easily detectable one will correspond to “yes”.