The evolution or change in organisms can be observed in nature.
The existing genetic variation provides natural selection with the material needed for changes in the population.
In the desert, plants that have glossier leaves will be better adapted to the dry conditions in the desert environment. As the climate changes the varieties of the plant with less glossy leaves were unable to survive and reproduce as well as plants with more glossy leaves. This will create a change in the population. This is an example of adaptive evolution.
A classic example in animal adaptive evolution is the peppered moth in England. Before the Industrial Revolution the peppered moth population was primarily white with a small minority of black moths. During the Industrial Revolution and the extensive use of coal the black variety was better adapted to the changing environment. After the use of coal sharply declined with the use of electric power, the white variety again was better adapted. The population went from mainly white, to mainly black, to back to mainly white.
Natural selection can only select from existing variations, Presently observed changes in the existing variations are all results of a loss of genetic information. Examples such as bacterial resistance , (see the Beak of the Finch page 260), resistance to malaria, and the blind fish of Death Valley are all due to the loss of genetic information.
Both animals and plants are subject to adaptive evolution and genetic changes due to loss of genetic information. Note Darwinian evolution is an unobserved extrapolation of the observed adaptive evolution. Neo Darwinian evolution postulates that random accidental mutations will result in an increase in information and complexity, which has never been experimentally observed.
