Music has structure at many levels, from grand arrangements of verses and choruses down to patterns in small riffs and themes. A bracketed L-system — the SARAH language — is used to represent compositions in terms of these hierarchical structures, allowing genetic programming to meaningfully mutate and crossbred compositions at all levels of structure. Automated composition becomes possible, using evolution with human aesthetic judgment as a fitness function. SARAH is also human-readable and can be used as a human tool for rapid structural composition development; or as a semi-automated composition system, mixing human and evolved contributions. The system has bred pleasing compositions starting from basic musical materials and has also been used to crossbreed Bach with the Spice Girls: these examples are presented as audio files.