a) There are many causes and types of extinction. Any species that is unable to survive or reproduce in its environment, along with the inability to migrate to a new environment where they can, will eventually die out and become extinct. However, even healthy species may become extinct as a result of toxic pollution creating an unlivable habitat or gradually when a species will eventually lose out in competition for food to better adapted competitors. When a new species is introduced into an ecosystem, the chances of that species taking over a niche already occupied increases, and will result in the extinction of one species or more. Humans can also cause extinction of species through over harvesting, pollution, habitat destruction, over hunting, and other influences.


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Pollution: A common cause of extinction of species




When environmental conditions change, processes of evolutionary change enable some species to adapt to new conditions and thrive. Species that fail to adapt to these ever-changing environments eventually become extinct. As increased variation of species in a particular clade heightens the chances of the clade surviving environmental change in some cases, another contributing cause to extinction could be the lack of variation of species within a clade. In accordance to clades, if the rate of speciation in a clade is equal to or greater than the rate of extinction, the clade will continue to exist. If the rate of extinction in a clade is greater than the rate of speciation, the clade will eventually become extinct. All species are constantly evolving and competing for resources. Some species just become extinct because of the slow and steady process of natural selection. This type of extinction, referred to as background extinction, is a type of extinction where there are no sudden, sometimes unexplained, extinctions of species. It is a natural process, much like death.

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Competition: May the best win and reproduce




However, mass extinction is completely different. It is when many species become extinct in a relatively short period of time. Species become extinct in mass extinction because their environment breaks down and the ordinary process of natural selection cannot compensate quickly enough. E.g. Asteroid crashes, large volcanic eruptions, moving continents, changing sea levels, etc. These are conditions that relate to rather large communities and ecosystems, and the causes are therefore much more large-scale.

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Asteroids: Dinosaurs' worst nightmare




b) Extinction plays the role of removing one type of species completely to allow other species to take over that removed species' niches, thus quickening the usual evolution process. Divergent evolution occurs as the new species take over different environments and niches (along with different selective pressures) and convergent evolution occurs as the new species develop and share similar traits with the extinct species, due to living in similar environments. Extinction paves the way (catalyst) in creating new species and allowing those species to steadily evolve to become more adapted to their environment and become better in filling its roles in the ecosystem they live in.

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The extinction of Dinosaurs allowed other species to fill the empty niches and evolve




Significance

Extinction is a very important process in evolution. Extinction provides evidence that evolution does occur and so does natural selection because why else would species become extinct? Species become extinct because they cannot adjust and adapt toe the pressures they receive from the changing environment and cannot compete with other species in order to survive and reproduce. Only species that are naturally selected, the ones that have evolved to better live in their local environment live on and not become extinct. Extinction also offers new opportunities to survivors. As species become extinct, the surviving species are able to fill the void of the empty niches which the extinct species made. This allows other species to grow and become a bigger part within their environment than they were before.