Final answer:
Tortoises evolving into different species on the Galápagos islands demonstrate allopatric speciation, where geographical isolation results in species divergence. These isolated populations develop unique adaptations, leading to the emergence of new species.
Step-by-step explanation:
Tortoises colonizing the different Galápagos islands and evolving into different species is an example of allopatric speciation.
Allopatric speciation occurs when populations of the same species become geographically isolated from each other. Over time, these isolated populations adapt to their specific environments and evolve genetic differences significant enough to prevent interbreeding. In the case of the Galápagos tortoises, the isolation of different islands led to unique adaptations such as different shell shapes that signified different species. This form of speciation reflects the principles of evolution that Charles Darwin observed in his studies of island biogeography during the voyage of the HMS Beagle.
Adaptive radiation is another evolutionary process closely related to allopatric speciation, where a single species evolves into several new species to fill different ecological niches. This can occur in island archipelagos, like the Hawaiian honeycreepers, which evolved from a single founder species into numerous distinct species due to geographical isolation.