The large finches now living on the Galápagos Islands differ from the original source population from a nearby island primarily due to a combination of factors:
- The separation of habitats reduced gene flow between the populations, limiting genetic exchange and allowing populations to diverge genetically.
- Natural selection favored individuals better adapted to the unique environments of each island, especially adaptations like beak size and shape suited to available food resources.
- Genetic drift also contributed to changes in the populations as random genetic changes accumulated independently in each isolated population.
- Environmental factors such as food availability and climatic events (e.g., El Niño) caused selective pressures that further shaped the evolutionary path of the finches on each island.
These processes led to the finches evolving distinct physical and behavioral traits that helped them exploit the ecological niches on their specific islands, differentiating them from their ancestors on other islands.
