Animal signals

SummaryThe study of animal signals began in earnest with the publication in 1872 of Charles Darwin’s The Expressions of the Emotions in Man and Animals, which laid the basis for a comparative study of signals across all animals, including humans. Yet even before Darwin, the exceptional diversity of animal signals has gripped the attention of natural historians and laymen alike, as these signals represent some of the most striking features of the natural world. Structures such as the long ornamented tail of the peacock, the roaring sounds of howler monkeys, audible kilometers away, and the pheromone trails laid by ants to guide their nestmates to resources are each examples of animal signals (Figure 1). Indeed, because signals evolved for the purpose of communicating (Box 1), their prominence can be hard for even a casual observer to overlook. Animal signals therefore raise many scientific questions: What are their functions? What information do they transmit? How are they produced? And why did they evolve?