What causes speciation?

Speciation occurs when a group within a particular species develops a set of unique characteristics which the other members of that species do not exhibit. The unique characteristics acquired by this group invariably distinguishes them and their offspring from their ancestors. Occasionally, all the members of the same species change into a new species over a period of time without any group splitting from the main species but this is a less common occurrence.

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Speciation is caused by reproductive isolation. Speciation is the process of creating a new species. A species is a group of organisms that can mate and produce fertile offspring. Fertile offspring means that the offspring have the ability to reproduce. So, when two organisms can no longer mate to produce fertile offspring, they are no longer considered to be part of the same species. There are typically 3 ways in which organisms can become reproductively isolated. They are behavioral, temporal, and geographic. Behavioral isolation is when the organisms are in the same area but the mating rituals/behavior differ, so they chose not to mate. Temporal isolation is when the organisms are in the same area, but the time of day/year that they mate does not overlap, so they do not mate. Geographic isolation occurs when two organisms cannot come in physical contact with each other due to geographic barriers such as rivers or mountains. Speciation is a very slow process and takes a long time. The longer two organisms go without mating, the more likely it is that they will evolve adapt to their environments differently, and it is these different adaptations that will lead to different species.
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How does speciation occur?

A species is a group of living organisms comprised of members capable of sharing a gene pool or interbreeding. This implies that members of the same species have similar characteristics and are closely related to each other. They are usually able to interbreed and produce fertile offspring. Speciation is an evolutionary process. Usually, some mutation occurs, leading to reproductive isolation, and it is this reproductive isolation that causes speciation.

Reproductive isolation can occur in three ways. The first is allopatric speciation. This occurs when members of a species split into geographically isolated groups as a result of events such as continental shift. The geographic barrier prevents members of both groups from exchanging genetic materials. Gradually, phenotypic and genotypic differences begin to appear between the two groups. Initially, the geographically separated group develops into an incipient species, but over time, the process of speciation progresses to completion with the formation of brand new species.

The second type of speciation is called parapatric speciation. This happens when interbreeding still takes place occasionally between the two groups in spite of the geographical barrier between them. Unlike allopatric speciation, parapatric speciation does not give rise to two distinct populations of different species. Instead, an environmental gradient of species is created. This type of speciation is common where distinct geographical barriers don't exist.

The third type is sympatric speciation, which can occur in the same geographical location if a group inherits more than one homologous set of chromosomes from their ancestral species. This character trait is called polyploidy. It is the rarest form of speciation.

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