Since the vocal tract consists of soft tissue (and therefore does not fossilise), reconstructing it depends on extrapolating from measurements made at the bases of fossil skulls.

ECONOMIST: What is music for?

There is also the "vocal tract" - everything upwards of the larynx along with the mouth, which are well known in humans to shape sung notes and subtle vowel sounds.

BBC: Helium-huffing gibbons 'sing with soprano technique'

But David Frayer and Chris Nicolay at the University of Kansas have, over the past couple of years, shown that it is at least equally plausible that Neanderthals possessed a vocal tract similar to a modern adult's.

ECONOMIST: What is music for?

Singing too has evolved, and soprano singers reach their piercing high notes by precisely controlling the shape of their vocal tract to match its natural, resonant frequency with multiples of the one being produced by their vocal folds.

BBC: Helium-huffing gibbons 'sing with soprano technique'

In humans the vocal tract acts as a filter on the sound from the source, and the "source-filter theory" held that the separate, fine control of the vocal tract to be the product of a long evolution in the development of the subtleties of speech.

BBC: Helium-huffing gibbons 'sing with soprano technique'