Natural Selection
Natural selection is a theory developed by Charles Darwin in which those with traits that fit the environment the most go on to survive and reproduce. (1) The reason the red fox is alive today is because of natural selection. Traits like a bushy tail, thick fur, and eyes with night-vision all contribute to the red fox thriving in it's environment. (2)
Evolution and Taxonomy of the Red Fox
Cladogram
Evidence of Evolution for the Red Fox
The red fox shares a common ancestor with all organisms, but is more closely related to vertebrates like reptiles, amphibians and birds. An example of evidence shown from this ancestry is shown through homologous structures. For example, bats, whales, and humans all share the same forearm bone as the red fox, but the external appearance is different because all of these organisms developed in different environments. (3) Also, the red fox shares a similar-looking embryo as fish, birds, and many other different organisms, but the outcome of the fetus is different because there are different genetic instructions for every organism. But embryology proves that the red fox shares a common ancestor with all organisms of the animal kingdom. (4) Also, a fossil of a two million year old Malapa fox showed striking resemblances to the red fox, which shows how past organisms are related to modern organisms existing today. (5)
Speciation
The red fox experienced allopatric speciation, which is the occurance of a new species by geographic isolation. This means that at one point, the red fox was in the same species as another fox, but that species got split up and evolved in different environments, creating two different species. Speciation can also be sympatric, but that only occurs in plants. In sympatric speciation, a plant will double it's number of chromosomes, creating an entirely new species. The new species will then self-pollinate to reproduce. (6)
(1) http://www.britannica.com/EBchecked/topic/406351/natural-selection
(2) http://www.pbs.org/wnet/nature/interactives-extras/animal-guides/animal-guide-red-fox/2212/
(3) http://itc.gsw.edu/faculty/bcarter/histgeol/paleo2/homol1.htm
(4) http://necsi.edu/projects/evolution/evidence/embryos/evidence_embryo.html
(5) http://www.sciencedaily.com/releases/2013/01/130123115350.htm
(6) http://www.uic.edu/classes/bios/bios101/Speciation2/sld022.htm
(2) http://www.pbs.org/wnet/nature/interactives-extras/animal-guides/animal-guide-red-fox/2212/
(3) http://itc.gsw.edu/faculty/bcarter/histgeol/paleo2/homol1.htm
(4) http://necsi.edu/projects/evolution/evidence/embryos/evidence_embryo.html
(5) http://www.sciencedaily.com/releases/2013/01/130123115350.htm
(6) http://www.uic.edu/classes/bios/bios101/Speciation2/sld022.htm