Blues licks (the blues-guitarist's melody) originated when Africans tried to play their native microtonal melodies on American fretted guitars (which offer only two choices--major or minor). To compensate, they slurred "down and dirty" minor-tones toward "upbeat and clean" major tones, in a way that European music had never done, thus giving birth to American blues, rock, and jazz.
Blues licks here are grouped by difficulty. Heart-of-the-Blues is entry-level ("minor" blues). Soul-of-the-Blues is nominal-level (adds "major" blues to the repertoire of blues-guitarists already playing minor blues). Beyond-the-Blues is advanced-level (following-the-changes in all 12 dominant keys).