Natural selection

Natural Selection is the mechanism by means of which random mutations of the chromosomes of individuals in a population of one species result in the non-random survival of those individuals in whom the mutation confers an advantage over those without the mutation. While it is believed that most mutations are lethal, resulting in the individual's death, some mutations are not, and can prove helpful to the individual. For example, if a mutation in a gene changed the color of a white moth to black, the population might, over time, evolve a preponderance of black individuals if that helped them to hide more effectively from predators. This was actually observed in England where a white species of moth became black over time during a period when the Industrial Revolution had coated many trees and buildings in black soot against which a white moth would stand out clearly to any predator.

Over time natural selection not only results in minor changes in a population, but can result in the evolution of a new species when part of a population is isolated from the rest for geographical or other reasons. The great genius Charles Darwin, who coined the term, noticed how certain species of finches in the Galapagos Islands, that did exist anywhere else, seemed to be related. He hyopthesized that a pair of one species of finch may have been blown to the isolated islands from the mainland of South America during a storm. As mutations occured in the population over time, in the absence of competion from any other species of birds, the birds gradually occupied habitat niches ordinarily occupied by woodpeckers (strong, long bill for digging in rotten wood for insects), insect-eating birds (small with thin bills), and seed-eating birds (heavy, strong bill for cracking seeds). Gradually isolated from each other by different habits and needs, the birds eventually evolved into several different species. The same has been observed of Australia, where a number of different marsupial species have evolved. Presumbably, when a land bridge connected Austrailia to Indonesia, an ancestral marsupial had arrived on the shores of Australia. After oceans rose and the island continent was isolated, this first marsupial species evolved to fit a number of different niches, including that of the dog-like Tasmanian Devil.