DIRECTIONAL SELECTION Meaning and
Definition
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Directional selection is a concept in evolutionary biology that describes a form of natural selection in which a certain phenotype or trait becomes more prevalent in a population over time. This occurs when individuals with extreme phenotypes are favored and have increased reproductive success, leading to a shift in the overall distribution of the population towards a particular direction.
In directional selection, individuals with traits that are advantageous in a specific environmental context are more likely to survive, reproduce, and pass on their genes to the next generation. As a result, the frequency of these advantageous traits increases while the frequency of less beneficial traits decreases. This shift in phenotype distribution is driven by environmental pressures that favor a particular extreme of the phenotypic range.
For instance, if a population of birds inhabits an area with gradually declining vegetation, directional selection may favor longer beak lengths as they allow the birds to reach scarce food resources more effectively. Over time, the average beak length in the bird population will increase as birds with longer beaks have a greater survival advantage and produce more offspring. This results in the population becoming more adapted to the changing environment.
Directional selection can lead to rapid evolutionary changes as it acts to amplify the frequency of specific traits within a population. However, it can also reduce genetic diversity, as individuals with alternative traits are less successful and reproduce less often.
Etymology of DIRECTIONAL SELECTION
The word "directional selection" is derived from the combination of two terms: "directional" and "selection".
The term "directional" originates from the Latin word "directus", which means "straight" or "direct". In this context, "directional" refers to something that has a specific trend or tendency in a particular direction.
The term "selection" comes from the Latin word "selectus", which means "chosen" or "selected". It refers to the process of choosing individuals or organisms with certain traits or characteristics for reproduction, leading to a change in the overall genetic makeup of a population.
When these two terms are combined, "directional selection" refers to a mechanism of natural selection in which individuals with traits that deviate from the average of the population have a higher survival and reproductive success.
