What is Natural Selection?
Some degree of variation exists in all population of organisms. The cause of this is partly the random mutations that can occur in the genes of a single organism. These mutations can be passed to the offspring through their parent organism. Throughout the lifespan of an organism their genomes interact with the environment around them and this causes a variation in their traits.
Organisms with certain favourable traits have a higher chance of surviving in their environment long enough to reproduce and pass on the favourable traits to their children. The other cause is the effectiveness of reproduction for that organism. Therefore the population evolves, and the most favourable traits see propagation into future generations while the unfavourable ones are lost. Over time this process may even result in birth of a new species.
For instance consider the simple example of a rabbit. A rabbit that runs fast will have a better chance of escaping predators than one that runs slower. Thus the rabbit that is faster will survive longer and will be able to procreate more and pass on its trait of faster speed to more offspring than the rabbit that runs slower will. This will cause an increase in the population of faster rabbits compared to slower rabbits in the next generation.
While in reality this hereditary advantage might be a very slight, but eventually over the course of many generations the rabbits that have the faster trait will become dominant in the population. This way the environment of an organism, naturally selects the best traits, that are favourable for an organism and are passed on to their next generation, gradual bringing a change or, we can say causing evolution.
Also related to natural selection is the famous phrase, "survival of the fittest". While the literal meaning of the phrase seems to point out that the fittest organism survives the longest; however in case of natural selection fittest has a slightly different meaning. Fitness can be measured as an average of an entire population. That is instead of focusing on the longevity of one individual organism, it focuses on the entire population and their average lifespan. For instance a short lived organism with favourable traits might reproduce more times than a long lived one, hence successfully passing its favourable traits to more offspring.
Natural selection can act on most any heritable trait of an organism and any aspect of the environment can produce selective pressure on that trait including sexual selection, which refers to competition for mating and reproducing. But this does not mean that natural selection always results in evolutionary adaption to environment. It can also simply mean that the less fit variants of the species are eliminated, thus maintaining the status quo in the population.
The idea of Natural Selection has had wide ranging impacts on our society ever since its conception. Most importantly it supported the theory of evolution of the human species and called into question the previously wide spread theories that were based on the creation of all living organisms by supreme beings like Gods.
However this theory was also used for more negative purposes like Social Darwinism, which is basically the ideology of applying this theory to sociology and politics. It was used as a justification for colonization by claiming it brought progress to backward people, citing the superiority of the white race, and later used by the supporters of Nazism as a justification for the Holocaust.
All these things said, the fact remains that the theory of Natural Selection had an immense impact on the development of modern thought and society.
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Edited by: Rajesh Bihani ( Find me on Google+ )