Evolution, the unifying theory of biology, describes a mechanism for the change and diversification of species over time.
Charles Darwin and Alfred Wallace independently developed the theories of evolution and its main operating principle: natural selection.
The differences in shape and size of beaks in Darwin's finches illustrate ongoing evolutionary change.
Natural selection can only occur in the presence of genetic variation; environmental conditions determine which traits are selected.
Evidence for evolution has been obtained through fossil records, embryology, geography, and molecular biology.
There are many misconceptions about evolution, including the meaning of the word theory, the way populations change, and the origin of life.