Darwin's finches is the classic example of --------------------.

Step-by-step solution

Darwin's finches are a classic example of adaptive radiation and allopatric speciation, which occurs due to geographical isolation. The finches migrated to the Galapagos Islands and became geographically isolated from the mainland population and from each other on different islands. This isolation prevented interbreeding and allowed them to evolve into distinct species adapted to different ecological niches. Answer: Geographical isolation