Diving requires a special anatomy of the airway entrances and a very refined control of breathing.
Later, the evolution of association areas in the brain greatly enhanced human ability for attaching a particular meaning to a conventional sound combination. The ability to speak is a uniquely human characteristic. Innumerable attempts to explain it have been made but the question of how language emerged is not yet solved. When surfaced they open the airway passage whenever they want to inhale air, and they can hyperventilate and then close the airway passage when they intend to dive. All of this is very speculative but interesting enough to elaborate the hypothesis of the aquatic origin of speech and to propose a possible scenario for speech emergence.