The Galapagos are a group of islands located approximately 1000 km from the coast of Ecuador. Due to this, the finches on Galapagos live in isolation from those on the mainland and thus, very little gene flow occurs.
This has enabled the evolution of new finch species that can only be found on these islands. These endemic species are a perfect example of allopatric speciation in which, an ancestral population evolves into new species due to isolation caused by geographic barriers.
The speciation of the population that started living on the islands is somewhat more complicated. The distances between the islands are much smaller and although not common, some individuals do move between the islands. Thus, there is some gene flow.
Peter and Rosemary Grant have closely studied the Galapagos finches and their evolution for 30 years. By studying the distribution of break depths and lengths, they have made some exciting discoveries.
Due to changes in the rainfall, the seeds size and number differ from year to year. Thus, different beak sizes will be favored at different times. The beak size and depth is transmitted genetically and thus is heritable.
Favorable traits will enable the individual to produce more offspring and thus are said to be "naturally selected". Due to rainfall differences and thus seed production, the Grants could observe the effect of natural selection on beak dimensions and sex ratio within only a few years. This was extremely surprising as Darwin believed that evolution is takes such a long time, that we are unable to observe it directly.
Furthermore, the evolutionary changes were so small (only 0.5mm) that they would not be detected except though careful measurements.
Evidence of hybridization has also been observed, which will produce offspring with a beak size intermediate to that of their parents.
