The hamlets, a group of reef fishes from the wider Caribbean, sport a stunning array of colours and patterns, but the genetic basis of this morphological variety is unclear.

Although the hamlet lineage is about 26 million years old, the diversification of colours appears to have occurred only within the last 10,000 generations in a burst of diversification that ranks among the fastest in fishes.

Adaptive radiation, the evolutionary process whereby a lineage diversifies over a short period of time, often occurs in geographically isolated or newly formed habitats where colonising species encounter unoccupied niches and reduced selective pressures.

Genomic analysis suggests that colour pattern diversity is generated by different combinations of alleles in a few genes with a large effect.

Such rapid phenotypic diversification has also been documented in some butterflies and finches, which are other examples of tropical radiations that took place in highly diverse and complex environments.