The process of natural selection throughout the history of life on Earth has resulted in the success of some species and the extinction of other species. Why has natural selection not resulted in the existence of a single best-adapted species?
1 Answer
Natural Selection can only select from existing variations. Natural Selection does not create or form information.
Explanation:
First a single best adapted species would not be the best adapted species. Organisms must live in balance with their environment which includes other organisms. A single species would soon go extinct because it would create an imbalance.
Second natural selection does not create or form variations which might result in the improvement of the species. Natural Selection can only select from existing variations those that are best adapted to the present environment.
According to Neo Darwinian theory any "improvements" come from random mutations in the DNA. Natural selection can then sort the mutations. Those mutations that help the organism to survive the environment will survive and on their DNA. Those mutations that do not help the organism survive in that environment will not survive to pass on their DNA.
Examples of harmful mutations that are beneficial to survival would sickle cell anemia. bacterial resistance to antibiotics due to gene loss, and the blind fish of death valley. In a normal environment these mutations are harmful resulting in a loss of information. But in a changed environment the mutations aid in survival.
An example a single best adapted species might be the Cheetah.
The African Cheetah is so well adapted to its environment that there is almost no genetic variation within the population. This leaves the Cheetah vulnerable to extinction do to an environmental change. Natural selection would cause the existing Cheetah population to die out. With no existing variations to "choose" from the Cheetah would become an extinct species.
