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The ability to communicate with conspecifics is an adaptive behavior important for survival and reproduction, particularly in lineages that evolved enlarged brains and complex social behavior. In humans, language is supported by a robust, left-lateralized white matter fiber tract called the arcuate fasciculus, which links Broca’s and Wernicke’s areas, the core neocortical language regions located in the frontal and temporal lobes, respectively1. This tract is also present in chimpanzees, less substantial than in humans and either weakly leftwardly-asymmetric or not asymmetric2. Other mammalian lineages have evolved large brains, complex behavior and social communication in parallel with primates, notably including carnivores. In dogs (Canis familiaris), domestication has almost certainly involved additional selective pressures and environmental factors that have shaped the evolution and development of neural circuits for communication. We report that the dog brain possesses a large, left-lateralized white matter tract that links cortical centers for productive and receptive communication, and that this tract is positively associated with individual variation in receptive vocabulary size. 

Many researchers consider language to be definitionally unique to humans. However, increasing evidence suggests that language emerged via a series of adaptations to neural systems supporting earlier capacities for visuomotor integration and manual action. This paper reviews comparative neuroscience evidence for the evolutionary progression of these adaptations. An outstanding question is how to mechanistically explain the emergence of new capacities from pre-existing circuitry. One possibility is that human brains may have undergone selection for greater plasticity, reducing the extent to which brain organization is hard-wired and increasing the extent to which it is shaped by socially transmitted, learned behaviors. Mutations that made these new abilities easier or faster to learn would have undergone positive selection, and over time, the neural changes once associated with individual neural plasticity would tend to become heritable, innate, and fixed. Clearly, though, language is not entirely “innate;” it does not emerge without the requisite environmental input and experience. Thus, a mechanistic explanation for the evolution of language must address the inherent trade-off between the evolutionary pressure for underlying neural systems to be flexible and sensitive to environmental input vs. the tendency over time for continually adaptive behaviors to become reliably expressed in an early-emerging, canalized, less flexible manner.