There are many types of evidence to support Natural Selection Theory. For instance, one can observe homologous structures between species. A classic example is the human forelimb, the bat wing, the whale flipper, the bird wing and a frog limb. All have a variation on the same theme and all of the bones are present in each creature, although modified to adapt to a different niche and environment. These suggest evolution from a common ancestor. Another type of evidence to support Natural Selection is the fossil record. Obviously, we can observe ancestral forms of present day life and because of time and the inheritance of various adaptations, the ancestral form will look like a more primitive version of the modern one. Also, we see extinct life forms in the fossil record indicating that both the Earth and the organisms on the Earth are constantly changing. Other evidence to support Natural Selection is biochemical evidence. The DNA of organisms that are closely related will have less genetic differences, than those who are more distantly related. Sometimes, a gene that is highly conserved with very few modifications such as cytochrome c, indicates evolution from a common ancestor especially when most living things have that gene. Evidence to show that Natural Selection is an ongoing process can be seen in the study of Biston betularia, or the peppered moth. Pre-Industrial Revolution England saw about 99% of these moths with a light color and 1% dark moths which existed as a genetic variation. The trees were light colored and the light ones evaded capture by predatory birds as they blended into the background of the tree trunks. The dark ones were eaten and the agent of selection were the birds who ate them. After the Industrial Revolution, coal smoke left soot in the air and this caused the tree trunks to become darker. Being light colored in this new environment was a disadvantage, and in a few short years, a reversal occurred with most moths being dark as they blended into the background and escaped being eaten, and the light ones decreasing. However, once England adopted clean air laws, the light moths, once again outnumbered the dark. Although this example doesn't illustrate the evolution of a new species of moth, it shows the relationship between adaptations an individual has that aid in its survival and the environmental conditions that are constantly changing. These conditions ultimately lead to Natural Selection.