Natural selection is an evolutionary process, originally proposed by Charles Darwin in his seminal On the Origin of Species, during which different individual organisms develop characteristics that lead to the species’ future survival over the course of several generations. Organisms that have these preferable characteristics automatically become more likely to reproduce by the sheer nature of their ability to survive in otherwise adverse conditions. Natural selection can also be called microevolution because the adaptation takes place one step at a time as opposed to an immediate species-wide change. For microevolution to give way to macroevolution – the development over time of wholly new species or specialized organs such as the eye – the principles of divergence and extinction must come into account. As explained by Reznick and Ricklefs (2009), divergence occurs when a certain species evolves several distinct variations based on environmental factors. Not all these variations will be successful organisms, but those that survive will continue to evolve with multiple variations in a similar manner to their parent species. Over time, different “branches” of a species’ evolutionary tree may go extinct, severing the hard link between two divergent species that share biological ties from a common ancestor. These changes take place over the course of hundreds, if not thousands, of years, which explains why we are unable to see such drastic macroevolutionary changes take place within a typical human life. This process of repeated divergence and extinction supports Darwin’s Theory of Evolution because it accounts for the diversification of species based on local environments. For example, there are many different varieties of rodents, all evolving from the same base species, but a guinea pig isn’t suited to survive in a desert the way a kangaroo rat is, because guinea pigs were borne out of spending years in a completely different environment than kangaroo rats. The evolution is evident since they are both rodents, but the variations on a microevolutionary level lead to eventual macroevolutionary change.
Reznick, D. N., & Ricklefs, R. E. (2009). Darwin's bridge between microevolution and macroevolution. Nature, 457(7231), 837-842.
Natural selection. (n.d.). Dictionary.com Unabridged. Retrieved March 10, 2014, from http://dictionary.reference.com/browse/natural+selection