Three arguments are advanced from human and nonhuman primate infancy research for the exaptation of ingestive mouth movements (tongue protrusion and lip smacking) for the purposes of social communication: their relation to affiliative behaviours, their sensitivity to social context, and their role in social development. Although these behaviours may have an aerodigestive function, such an account of their occurrence is only partial.

In this book it has been proposed that the mirror system can be a scaffold for building a language-ready brain, because of its property of matching action observation with action execution, a feature that can correspond to the “parity” requirement for communication. In this commentary we will first emphasize two properties of mirror neurons and motor cortex that may have contributed to language: the generalization of the property of understanding action goals and the capacity to decode the goal of action sequences. Then we will propose, based on recent behavioural and neurophysiological data in monkeys, that the vocalization in non-human primates could have reached a partial voluntary control, thus contributing to the emergence of a communicative system relying on the coordination of gestures and utterances.

Based on mirror neurons' properties, viewers are emotionally engaged when observing others – even when not actively interacting; therefore, characterizing non-participatory action-viewing as isolated may be misleading. Instead, we propose a continuum of socio-emotional engagement. We also highlight recent developmental work that uses a second-person perspective, investigating behavioral, physiological, and neural activity during caregiver–infant interactions.

Empathy is the phenomenal experience of mirroring ourselves into others. It can be explained in terms of simulations of actions, sensations, and emotions which constitute a shared manifold for intersubjectivity. Simulation, in turn, can be sustained at the subpersonal level by a series of neural mirror matching systems.