Teaching with evaluation in ants.

Tandem running in ants is a form of recruitment in which a single well-informed worker guides a naive nestmate to a goal [1-8]. The ant Temnothorax albipennis recently satisfied a strict set of predefined criteria for teaching in nonhuman animals [9, 10]. These criteria do not include evaluation as a prerequisite for teaching [10]. However, some authors claim that true teaching is always evaluative, i.e., sensitive to the competence or quality of the pupil [11-13]. They then assume, on the premise that only humans are capable of making such necessarily complex cognitive evaluations, that teaching must be unique to humans. We conducted experiments to test whether evaluation occurs during tandem running, in which a knowledgeable ant physically guides a naive follower to a goal. In each experiment, we interrupted the tandem run by removing the tandem follower. The response of the leader was to stand still at the point where the tandem run was interrupted. We then measured how long the leader waited for the missing follower before giving up. Our results demonstrate T. albipennis performs three different kinds of evaluation. First, the longer the tandem has proceeded the longer the leader will wait for the follower to re-establish contact. Second, ant teachers modulate their giving-up time depending on the value of the goal. Finally, leaders have shorter giving-up times after unusually slow tandem runs.