There are reasons to believe that they produced gibbon-like territorial songs. If this is so, it seems to imply that the earliest hominoids were monogamous. In that case, the great apes must have lost the more musical gibbon-like utterances. The adult males develop large laryngeal air sacs. It is not known which brain structures the gibbons use for song generation and analysis.
Great apes show slight Sylvian enlargements of the left auditory cortex.
Aquatic mammals can close the airway entrances much more completely than land mammals, thus avoiding being drowned by water entering the lungs, and they have a very refined voluntary control of mouth, nose and throat passages. Modern man has a very special anatomy of the airway entrances that is not incompatible with a previous semi-aquatic lifestyle. Just in front of that enlarged Area 4 lies Broca s Area. Figure 1 Lateral view of left human cerebral cortex. When our ancestors returned to a wholly terrestrial habitat, airway control for diving became superfluous and the refined airway musculature could be used exclusively for improving vocalisation.