similar characteristics.
Generation after generation, the population can change.
The important point is that natural selection does not work because organisms consciously decide
to evolve. A bird does not develop a different beak because it wants one.
Instead, variation already exists, individuals differ in their chances of surviving and reproducing,
and inherited characteristics can become more or less common over many generations.
This process can produce adaptation.
An adaptation is an inherited characteristic that helps an organism function successfully in a
particular environment. Thick fur can help an animal survive cold conditions. Certain root systems
can help plants obtain water. Specialized body structures can help organisms feed, move, or
avoid predators.
But an adaptation is always connected to an environment.
A characteristic that is useful in one environment may provide little advantage in another.
Darwin's ideas were strongly influenced by his voyage aboard HMS Beagle. During the voyage,
he collected specimens and made observations in many parts of the world. The Galápagos
Islands became particularly important in the development of his thinking.
Darwin noticed similarities and differences among organisms on different islands. The famous
Galápagos finches later became an important example of adaptive diversification, although
Darwin's understanding of them developed gradually and was supported by later scientific work.
The broader idea was that populations could become different when separated and exposed to
different environmental conditions.
Over very long periods, such differences can contribute to the formation of new species.
But what exactly is a species?
In biology, species are often defined using the biological species concept as populations whose
members can interbreed and produce fertile offspring. This definition is useful for many
organisms, but it does not apply perfectly to every form of life.
For example, scientists use different approaches for organisms that reproduce asexually or for
populations where boundaries are complicated.
Speciation—the process by which new species arise—can happen through several mechanisms.
One important pathway occurs when populations become separated. Geographic isolation can
reduce gene flow between groups. As mutations, natural selection, genetic drift, and other
