Stabilizing Selection & Diversifying Selection
Natural selection is a mechanism for evolution. Simply put, the individuals best suited to a certain environment thrive and reproduce, while other, less adapted individuals die without reproducing. No environment can support an unlimited population, so individuals within the population have to compete with each other for resources and mates. Eventually, unfavorable traits can be bred out entirelys. As the individuals in the population express more advantageous traits that make them more successful than their peers, these special individuals out survive and out mate their peers.
These are the basic principles of natural selection. While some of these were already being discussed at the time, most of the idea of natural selection is credited to Charles Darwin.
- Variation and Heredity: All individuals within a species are unique, with their own special variations in body and behavior. Some of these variations will be inherited by their offspring.
- Overproduction: More offspring will be produced than can survive.
- Limited Resources: No environment has unlimited carrying capacity. Survival and reproduction is determined by competition for limited resources, including habitat, mates, and food.
- Fitness: Some individuals have genetic variations that give them distinct advantages withing their environment. These individuals will survive and pass on their traits better than those without such favorable traits.
- Genetic Composition: As a species moves forward by generations, each new generation will have a higher percentage of individuals with advantageous traits than the last.
Types of Natural Selection
- Stabilizing Selection: This results in a decrease in a population's genetic variance and occurs when natural selection favors an average phenotype rather than variations.
- Diversifying Selection: This increases the genetic variation in a population and occurs when natural selection favors two or more extreme phenotypes that each have specific advantages.
- Directional Selection: This occurs when a population's genetic variance shifts toward a new phenotype and is caused by exposure to environmental changes.
- Kin Selection: This occurs when natural selection favors a trait that benefits related members of a group.
- Sexual Selection: Natural selection favors traits that maximize the ability of an individual to compete for mates and produce offspring. In the case of traits that help attract mates, like vibrant coloring, this can actually endanger the individual. While it does help attract mates, it also makes the individual easier to find by predators.