Zhenbiao Yang

that the retinal image contains a thorn). But is this ‘communication’? Among influentialists, there is ongoing debate about whether attention should focus mainly on signalers or receivers. The correct answer is probably “both” [9]. The chapters in this volume reveal little consensus regarding these, and many other, interesting questions. Despite numerous virtues, Wiley’s proximate definition of ‘signal’ would seem inadequate to many researchers interested in the evolution of communication. A prominent issue in this subfield is the question of ‘honesty’ in signals: under what conditions do signals provide perceivers with accurate information about the signaler, or the world? Evolutionary interests of signalers and receivers may often be different, leading to a constant selection for exaggeration and “dishonest” signaling (in this context, these terms carry no connotation of conscious deception). When signalers are, on average, deceptive, this should select for perceivers who ignore them [ 0], leading some to claim that only signals whose honesty is underwritten by a large ‘handicap’ cost to the signaler can be stable over evolutionary time [ ]. But this claim is now known to be overly broad, since honesty without handicaps can exist either when the interests of signaler and receiver roughly coincide, or if signal accuracy is underwritten by physical constraints (e.g. if only large animals can produce low-frequency resonances [ 2]). Such theoretical discussions require terminology that goes beyond proximate mechanisms, framing signaling as an adaptation in the strict Darwinian sense. This proximate versus ultimate debate is another false dichotomy, and the pluralistic perspective laid out by Tinbergen [ 3] provides the best way forward. Tinbergen emphasized that there is no conflict between ultimate and proximate explanations in biology, and that full understanding requires biologists to seek answers to both types of questions. In favor of mechanism, it is easier to observe a perceiver’s response to a signal than to rigorously determine if a particular signal is an adaptation: adaptation is an ‘onerous concept’ to be invoked only after plausible alternatives have been ruled out [ 4]. Nonetheless, a rich understanding of animal communication requires us to develop and test adaptive hypotheses about ultimate function. There is thus no real conflict between the diverse ultimate and proximate approaches to signaling adopted in this volume. In summary, this is an extremely thought-provoking book that broadly captures the current state of play in these multiple ongoing debates. The diversity of opinions, each concisely expressed in relatively short chapters, is its key virtue. While many key issues are opened but not resolved, the book would provide an excellent focus for a discussion-oriented seminar on animal communication. For biologists studying animal communication, many chapters will be required reading, because they clarify that considerable work is still needed to place communication research on a firm theoretical foundation with clear consensus about terminology and practice. The volume raises and clarifies, without answering, numerous questions that any future theoretical framework must successfully address.