Not so much evolved from the cuirass as it was a piece of medieval armour; the gorget-the piece of armour that protected the neck and came between the helmet and cuirass. As firearms became more prevalent on the battlefield; armour became less and less needed and various items of the medieval suit of armour were discarded, until by the seventeenth century, all that remained was the cuirass, gorget and helmet.
As military uniforms as we know them today began to be used (and firearms became more powerful) during the late 17th to 18th centuries, this became reduced down to just the gorget; which became the distinguishing mark of an officer during the 18th century, and gradually became smaller and smaller until it became the small crescent of metal you usually see in paintings and portraits of the time. Thus, any depiction of a soldier of the time would be depicting an officer.
Gorgets were gradually replaced by rank insignia worn on the shoulders of the uniform (epaulettes), but a vestige still exists in the 'gorget patches' worn by officers of general rank on the collar of their uniforms (and originally worn to hang the gorget from).