More seriously, classifying music into genres is like classifying animals into species.
It has no intrinsic value or meaning, it's just a handle that helps human beings conceptualise how different music/animals are related.
For animals cladistics (bases of common ancestors) is far more objective and insightful, similarly a Pete Frame Family Tree tells you a lot more than grouping bands by genre.
It's an analogy that will stand a fair degree of stretching, even if it isn't perfect.