DISRUPTIVE SELECTION Meaning and
Definition
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Disruptive selection is a form of natural selection that occurs when extreme traits in a population are favored over intermediate traits, leading to the splitting of the population into two or more distinct groups. This type of selection acts against the average individuals in a population, favoring those individuals at the extremes of a trait distribution.
In disruptive selection, there is a shift away from the average or intermediate phenotype toward extreme phenotypes. This can happen due to changes in environmental conditions, predation pressures, or competition for resources. The extreme phenotypes become more successful in their respective ecological niches, while the intermediate forms struggle to survive and reproduce.
As the extreme phenotypes become reproductively isolated from each other and the intermediate forms, they start evolving independently, potentially leading to the emergence of new species. Disruptive selection drives diversification and speciation as it creates distinct populations that are adapted to different ecological roles.
An example of disruptive selection is the divergence of beak sizes in a population of finches. If a population of finches lives in an area with a variety of seed sizes, individuals with large beaks are better suited to crack larger seeds, while individuals with small beaks are more adept at cracking smaller seeds. Over time, the intermediate beak sizes become less fit, and the population splits into two groups, each with distinct beak sizes specialized for a specific seed size.
Etymology of DISRUPTIVE SELECTION
The word "disruptive" in "disruptive selection" originates from the verb "disrupt", which comes from the Latin word "disruptus", meaning "broken apart" or "shattered". The term "selection" refers to the process of natural selection, which describes the differential survival and reproduction of individuals in a population.
The concept of disruptive selection was first introduced by the English biologist Ronald Fisher in 1930. It describes a form of natural selection where extreme phenotypes are favored over intermediate forms. This disruptive process can lead to the creation of two distinct subpopulations with contrasting traits.
Therefore, the term "disruptive selection" refers to the phenomenon where extreme variations of a trait become favored in a population, leading to the divergence of phenotypes and potentially the formation of new species over time.
