Researchers have provided the first experimental evidence that brain regions can evolve independently of each other during cognitive evolution. This so called mosaic brain evolution was verified empirically in an artificial selection experiment with guppies (Poecilia reticulata) where telencephalon size (but no other regions) differed by 10 percent after only four generations of selection. The findings can have wide implications for the understanding of cognitive evolution in other vertebrates, such as primates and humans.