Adaptive Radiation

Adaptive radiation is the rapid diversification of a group of organisms from a single ancestral species into many new forms, typically set off when environmental change opens up new resources or ecological opportunities. Darwin's finches are a classic case: around fifteen species descended from a single ancestor that reached the Galapagos roughly three million years ago, each evolving a beak suited to a different food source, from cracking tough seeds to probing for insects to feeding on cactus nectar. The cichlid fishes of Africa's Great Lakes, with roughly 2,000 species across Lakes Tanganyika, Malawi, and Victoria, are the most species-rich modern example, filling ecological roles that elsewhere are divided among several fish families, and Hawaii's honeycreepers, silverswords, and lobelioids each underwent their own separate radiations on the islands. Adaptive radiation is generally triggered by the loss of competitors or predators, the evolution of a key innovation, dispersal into an isolated environment full of unfilled niches, or a mass extinction that clears ecological space, any of which can reduce competition enough for a population to diversify into it.