Many species are known now to possess more or less consistent asymmetries (structural, behavioural or both) at a population level. The left hemisphere (LH) of the brain may be specialized for learned discriminatory behaviours, sensory and motor, upon which communication was grafted, perhaps on more than one occasion, and which may have left a residual mediation by the right hemisphere (RH) of emotional and spatial behaviours. Indeed, largely similar computational machinery on opposite sides of the brain can subserve both spatial processing and communication. Human bipedalism may have been pre-adapted for by retained arboreal habits, and selected for by thermoregulatory needs and foraging behaviours. While it would have permitted the slow development of tool use, the latter was probably insufficient to drive the rapid increase in brain size and the advent of language proper. Language, with probably a long prior evolutionary history continuous with primate vocalizations, probably did not arise via gesture. Though now effectively unique, its apparent sudden appearance around 50,000 years ago, judging by a transition in the archaeological record of art and artifacts, may merely reflect the attainment of a critical state in society, communication and technology. Until then there had been an interactive coevolution of brain capacity increase, social interaction and parenting with language a byproduct of demands imposed by such circumstances. Dextrality may be a consequence of LH mediation of communication and of other serial, syntactic, manipulatory behaviours (not restricted to the right hand); if not ancestral, it may have been sharpened by the need to communicate such behaviours (by imitative learning), but only when tool use and manufacture reached a comparatively late stage of sophistication, e.g., as in Homo erectus.