5.1 - B - Speciation
When populations of species becomes separated by some means, it is possible for natural selection to affect them differently. Over time, the populations can evolve in different ways such that they develop distinct characteristics and lose the ability to interbreed. When this happens, speciation has taken place and two new species emerge.
Speciation usually occurs when populations migrate to neighboring areas. When Darwin traveled to the Galapagos, he observed variations of similar species that had migrated between islands and developed unique characteristics. Watch the video at the bottom of the page for a great explanation of speciation in bird populations.
The example that Darwin noted was the red grouse (right) of Britain and the willow ptarmigan of Norway (left), which are commonly classified as two species. The idea of continuous variation supports the idea that evolution changes populations and that new species can result from this.
A commonly discussed change in a species' characteristics is the development of melanistic (dark) insects in polluted areas. The most famous example of this is the peppered moth, which was observed by British ecologist H.B.D. Kettlewell.
During the middle of the eighteenth century, the industrial revolution began which led to tons of soot being deposited in the countryside. This increase caused the surface of trees and rocks to darken. Peppered moths were a light-colored insect that used the bark of trees for camouflage. However, when the trees darkened they were no longer able to do so and so experienced increased predation.
A variant of the peppered moth emerged, which was darker in color. The variant blended in with the soot-stained trees and so were better able to survive. Over time, the number of dark moths increased while the lighter-colored moth population diminished.