show Abstracthide AbstractWhole-genome resequencing data of haplochromine cichlid fishes from the Lake Victoria Region associated with the publication by Meier et al. in Science 2023. In Africa's Lake Victoria region one cichlid lineage radiated in every lake, with the largest radiation in a lake under 20,000 years old. We show that all its species and ecological guilds evolved in situ. The history of the radiation is one of cycles of fusion (hybridization) and fission (radiation). It began after swamp-dwelling refugial populations, themselves of older hybrid descent, fused which re-suspended old admixture variation. Each contributed a different set of ancient alleles from which the food web radiation rapidly assembled, involving additional fusion and fission events. Such cycles of fusion and fission make adaptive radiation fast and predictable.