Speciation example (1 of 5)
The branching points on this partial Drosophila phylogeny represent speciation events that happened in the past.
Speciation example (2 of 5)
The scene: a population of wild fruit flies is minding its own business on several bunches of rotting bananas, cheerfully laying their eggs in the mushy fruit.
Speciation example (4 of 5)
The populations diverge: Ecological conditions are slightly different on the island, and the island population evolves under different selective pressures and experiences different random events than the mainland population does. Morphology, food preferences, and courtship displays change over the course of many generations of natural selection.