Short answers, pulled from the story.
The double bass originated in Europe during the 15th century as a modern descendant of the violone. Scholars remain divided on whether this large string instrument evolved from the viol family or the violin family.
A typical double bass stands around six feet tall from scroll to endpin, though the more common size bass stands on average five and a half feet. Most professional orchestra bassists use fully carved instruments made from maple for the back, spruce for the top, and ebony for the fingerboard.
Until the 1990s, child-sized double basses were not widely available, preventing children from playing until they grew tall enough to handle a three-quarter-size model. Starting in the 1990s, smaller one-half, one-quarter, and even one-eighth sized instruments became more widely available.
Steel has largely replaced catgut because steel strings hold their pitch better and yield more volume when played with the bow. Professor Larry Hurst argues that without overwound gut strings invented in the 1650s, the instrument would surely have become extinct due to unplayable thicknesses needed for regular gut strings.
The earliest known concerto for double bass was written by Joseph Haydn in 1763, though it is presumed lost in a fire at the Eisenstadt library. The earliest known existing concertos are by Carl Ditters von Dittersdorf, who composed two concertos for the double bass and a Sinfonia Concertante for viola and double bass.