Cichlids had genetically diverged on opposite sides of the river
Ichthyologists Melanie Stiassny and Robert Schelly observed that the cichlids, which are known to evolve quickly in new environments, were genetically distinct on one side of the Congo from similar-looking cichlids on the opposite bank. The exceptionally strong currents of the Congo divide the populations. Though the river was only a mile wide at that point, the habitats were as isolated as if a mountain range had risen between them.
