What is biological adaptation and how is it relevant to life as we know it today?

Adaptation, in biology, process by which an animal or plant species becomes fitted to its environment; it is the result of natural selection's acting upon heritable variation. Even the simpler organisms must be adapted in a great variety of ways: in their structure, physiology, and genetics, in their locomotion or dispersal, in their means of defense and attack, in their reproduction and development, and in other respects.

EX. "The 14 species of Galapagos finches differ from each other mainly in beak structure and feeding habits. The birds are believed to have undergone adaptive radiation from a single ancestral species, evolving to fill a variety of unoccupied ecological niches."