Animal signals and symbolism

Human languages are symbolic. If we accept a broadly gradualist account of evolution, forerunners of the symbolism found in human languages should be observable in our closest relatives. After intensive training by humans, animals as different as great apes, dogs, sea lions, parrots, and dolphins have been shown to be able to learn, and in some cases to use, linguistic symbols with both humans and conspecifics. However, there is an absence of convincing and widely accepted evidence for symbolism in the use by non-human animals of natural communication systems in the wild. In addressing this apparent paradox, we provide definitions of fundamental differences between human symbolism and non-human communication systems and discuss foundational capacities for symbolism in non-humans. We argue that animal signals sometimes thought to resemble symbols are more likely (as proposed by Darwin) emotional expressions. We offer arguments about the evolutionary pressures that may have led to increasingly complex communication in the hominin line.