Short answers, pulled from the story.
Paul Broca identified a specific brain region in 1861 that caused severe deficits when damaged. Two patients unable to speak beyond monosyllabic words led to the discovery of expressive aphasia.
First words appear during the first year of life for typical development. Children progress through two or three word phrases before reaching three years of age, with short sentences emerging by four years old according to standard developmental milestones.
Normal human speech is pulmonic, produced with pressure from the lungs. This airflow creates phonation within the glottis located inside the larynx before being modified by the mouth and vocal tract.
The human vocal tract does not fossilize, making this absence of physical evidence a persistent challenge for researchers. Indirect evidence regarding hominid fossils has proven inconclusive when trying to map changes in the vocal tract over time.
Diseases affecting lungs or vocal cords include paralysis, bronchitis, and cancers of the throat. Disorders of the brain such as dysarthria and dystonia lead to poor speech production alongside hearing problems like otitis media with effusion.