One day, a finch met a new species of bird on the Galapagos Islands. Eventually the birds had attracted, causing them to sexually reproduce, which resulted in an offspring.
They produced an offspring, who was a combination of both parents. However, he had a bigger head, bigger body and he had different feet. This was due to the different alleles from both parents, causing genetic variation.
Because of his new features, he was able to adapt to his environment in a better way, like his beak, which developed, allowing him to acquire different food sources.
How did Darwin use the Finches to support his theory?
He later on met another bird and sexually reproduced, resulting in another genetically varied bird. As the generations increased, the variations increased, causing different phenotypes in the offspring.
These genetic differences are clearly shown in different generations as the size of their beaks enlarging, allowing the birds to catch their prey in a more easier manner and to vary their prey. Their beaks are quite similar to other species of birds shown above.
These Finches are the same species of birds, however with different variations, they have acquired different parts which allow them to increase their functionality.