Introduction

Animals show both impressive feats and surprising failures of recognition. On the one hand, we have the Mexican free-tailed bat mother finding her young in a maternity cave of a million bats. On the other we have the redwinged blackbird parent failing to eject from its nest the conspicuously different eggs of a brood parasitic cowbird. From the evolutionary point of view, the failures of recognition are, on the face of it, much more difficult to explain than the successes. Any treatment of the evolution of recognition systems, therefore, must consider both faces of recognition – the failures as well as the successes. This is the perspective I take in this paper, drawing my examples from the parent-offspring context.

A source of conceptual confusion in the analysis of ‘failures’ of recognition has been the tendency of investigators to equate ‘recognition’ with ‘discrimination’. Typically, recognition is operationally defined in terms of discrimination, an animal being said to recognize a particular individual or class of individuals if it discriminates that individual or class from others (e.g. discriminates its offspring from other, unrelated young). For successes of recognition, this operational definition is perfectly reasonable. A failure of discrimination, however, could imply either that (1) discrimination is not possible, a true failure of recognition, or (2) discrimination is not adaptive in this circumstance.