In many ways, the Gibson Brothers parallel another famous brother band in bluegrass, the Osborne Brothers. Both groups worked in the bluegrass market yet they grew to encompass elements of country, folk and roots music as well, without leaving behind their own roots.
Perhaps it is the duo format that allows for this experimentation, as maybe the compromises of a more democratic lineup don't lend themselves to taking chances. Whatever the reasons, Eric and Leigh Gibson created a collection of songs that look forward to a more expansive definition of bluegrass while mining the genre's traditions at the same time.
Eric's Farm of Yesterday is a good example, with lightly snapping drums in the background of a song about the changes in the farming life. Jericho and Just an Old Rounder likewise take folk song melodies and apply them to songs about courtship and the prodigal son, respectively.
When they cover a well known artist like Tom Petty (Angel Dream), instead of taking the Del McCoury approach of 'grassing it up to the hilt, they treat it more gently and apply the bluegrass instrumentation without taking away the airy, ethereal feel of the original.
The Gibson Brothers may not be doing it on purpose, but their willingness to mold their sound to fit the songs, rather than the other way around, means they are also molding bluegrass to fit their own idea of what it is to them.