One of the most obvious correlations seen between different genres of music is the progression of styles and fusions over time. Many newer genres are influenced by previously established styles and represent fusions or offshoots of older genres. For example, rock music has its origins in blues music from the early 20th century. Rock incorporated elements of blues into a new, amplified style with electric guitars that became popular in the 1950s and 1960s. Subgenres of rock like heavy metal, punk rock, new wave, and alternative rock emerged in later decades by blending rock with other influences.

Hip hop music has roots in disco, funk, and soul music from the 1970s. Emerging out of the Bronx in New York, early hip hop incorporated rhythmic spoken word (“rapping”) over breakbeats and funk samples. As the genre evolved, it absorbed influences from dance music, electronic music, R&B, pop, and global styles. Trap music, which became hugely popular in the 2010s, fused hip hop with Southern bass music styles like crunk and Miami bass. Reggaeton, a Spanish-language dance genre popular in Latin America, also emerged from hip hop, reggae, and Latin styles in the 1990s.

Electronic dance music descended from genres like disco, Italo disco, Euro disco, and house music that incorporated electronic production elements. House arose in Chicago in the 1980s, merging elements of disco, funk, and electronic music. Subgenres of house like acid house, garage, jump up, hardstyle, and dubstep incorporated influences from rock, pop, jungle/drum & bass, and global styles. Trance music’s melodic structure shows inspiration from new-age and ambient music genres. Bass music like dubstep brought polyrhythmic elements from genres like hip hop, garage, grime, and Jamaican dub/reggae forward in the mix.

Closely related styles often emerge from the same musical communities and regional scenes. For example, gothic rock, post-punk, and darkwave music styles arose simultaneously from overlapping scenes in Britain in the late 1970s/early 1980s that incorporated elements of punk, glam rock, and art rock with macabre lyrical and aesthetic themes. Folk punk emerged more recently by merging elements of folk, punk rock, and bluegrass in DIY communities. Lo-fi hip hop incorporated indie/bedroom production aesthetics into hip hop music.

Cross-genre correlations can also be seen in instrumentation, production techniques, and song structure. For example, country music has seen notable influence from blues, bluegrass, folk, Western swing, and rock and often incorporates electric guitars in addition to more traditional country instruments. Pop music frequently absorbs elements of other commercial styles like rock, dance, hip hop, R&B, and others to maximize mass appeal. Many popular song structures are based on traditional verse-chorus forms featured widely across genres initially defined as “pop music.” Electronic music often focuses on repetition and loops due to technological limitations of earlier gear and DJ/producer techniques.

Lyrical themes also provide some points of correlation between genres. Protest songs emerged across genres like folk, rock, punk, and others with messages of political or social change. Spiritual/religious themes show up widely in genres from gospel and Christian rock to worship secular songs. Coming-of-age and romantic themes recurs frequently as well, relating to universal human experiences. Drug culture and party/sex-focused lyrics appear regularly in genres like rock, punk, electronic, hip hop and beyond that celebrate excess or push boundaries. Storytelling traditions connect genres like folk, blues, rap, and flamenco that utilize lyrical narrative as a core component.

While many correlations exist due to influence and fusion between styles over time, genres remain broadly defined by core techniques, regional scenes, and social functions that differentiate them as well. For example, jazz prioritizes improvisation, complex instrumentation, and swinging polyrhythms not featured as prominently elsewhere. Classical music focuses on composed, notated art forms like symphonies, operas, and concert music. World music genres reflect deeply fusion folk traditions of various regions with culturally specific styles of instrumentation, vocal technique, dance, spirituality and storytelling endemic to a place. Ambient, new age, and meditative genres cultivate peaceful, hypnotic vibes through electronic soundscapes versus lyrics or driving rhythms prominent in other styles.

So While music genres certainly cross-pollinate due to the interconnected global music community, they maintain unique identifiers, histories, techniques and functions that distinguish specific styles from each other as well. Genres correlate where cultural transmission and influence have occurred, whether through timeline progressions, regional intersections, or social trend diffusion. But the diversity of human musical expression also leaves ample room for differentiation according to culture, place, and unique artistic vision. Understanding connections and distinctions between genres provides valuable insight into the social and artistic developments that have continuously shaped our musical landscape.