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The concept of species is fundamental in biology, representing a group of organisms that share common characteristics and can interbreed to produce fertile offspring. Various species concepts include the biological species concept, which emphasizes reproductive compatibility as the primary criterion. In this article, we will study the concept of species, their extinction, and more in detail.
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Species are the fundamental unit of biological classification, and they play an important role in differentiating the types of organisms. It is a group of individuals that can interbreed. The biological species concept and evolutionary species concept are the two known approaches to understanding the concept of species. Other approaches include nominalistic species, ecological species, typological species, and morphological species.
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Species are broadly categorized into six concepts, these are as follows:
This concept is very popular and introduced by the biologist Ernst Mayr in 1942. K. Jordan was the first one who worked on this theory and later Mayr supported this concept. They define the species as “interbreeding natural populations that are reproductively isolated from other such groups”. This theory emphasises more on reproductive isolation in defining the species which means organisms of one species do not interbreed with organisms of other species.
This prevents gene flow between populations and gene remains restricted within species. This concept does not focus on appearance in identifying the species rather they look on reproductive capabilities as prime criteria to define the species.
In the middle of the eighteenth century, Buffon and Lamarck proposed this idea in France. This idea holds that species are the creation of man. This approach lacks definite existence and does not hold any scientific basis. This theory believes that the species have been invented by nature and refer to it as big numbers of individuals jointly.
Also Read: Organism and Population
This concept of species defines it as a group of members sharing certain characteristics that distinguish them from other species. Earlier Aristotle and Plato stated this concept and later in 1954, Cain regarded this concept as morphological species concept because members of the species can be identified by their characteristics. Morphological species states that the species can be distinguished from other species by their physical or morphological features.
Define the species as a set of organisms that is adapted to a certain set of resources (a niche) in the environment. This concept explains why different species have different forms and behaviours; these adaptations are a result of the availability of resources. It demonstrated that the differences between species in form and behaviour are often related to differences in the ecological resources that the species exploit.
Also Read: Adaptation and Habitats
This is somewhat similar to the evolutionary concept of species which states that species are an irreducible group whose members are descended from the common ancestor. This concept defines species as a group which share a unique evolutionary history. This concept allows division of species into smaller groups. Although this concept contains flaws which make it infeasible to implement.
To address the limitation in biological species concept, evolutionary biologists formulated the evolutionary species concept. It was proposed by George Gaylord Simpson in 1951. George Simpson defines the species as a lineage of population that maintains its identity by evolving independently of other lineages. This theory is based on the fact that species undergo evolutionary changes in shape, size and other characteristics over the time. They define species as entities that are constantly evolving and adapting to their environment and applicable to both sexual as well as asexual reproducing organisms.
Wiley provided a revised definition to this concept of species in 1978. He defined the species as “an evolutionary species that are single lineage of ancestral- descendant population which draws its identity from other lineage and has its own evolutionary tendencies and historical fate”.
Also Read: Theories of Evolution-Explanation, Types, and FAQs
The term "species extinction" describes the irreversible disappearance of a certain kind of species from the biosphere of Earth. Throughout Earth's history, extinction has been a natural process, but in the present period, human activity has greatly accelerated it. It is believed that more than 99% of all species that have ever existed on Earth are extinct.
The estimated number of extinct species ranges from 10 to 14 million, of which over 1.2 million have been thoroughly examined and over 86% are still unknown. Major causes of extinction include Habitat loss,Climate change, Overexploitation, introduction of Invasive species, pollution and due to infectious diseases.
The key characteristics of biological species concepts are as follows:
The limitation of biological species concept are as follows:
Also Read: Difference Between Bacteria And Fungi
Biological and evolutionary species concepts are two different approaches to define and understand the basic concept of species. Although they share some similarities, they also have differences in terms of definition, criteria and emphasis. Key differences between these two theories are mentioned below.
Biological Species Concept | Evolutionary Species Concept |
|---|---|
This concept define species as the ability to exchange genetic material through reproduction. | This concept define species as lineage of population which maintain its identity over the time by evolving constantly to adapt to the environment. |
Prime criteria for defining species is reproductive isolation. | Focus on evolutionary and historical aspects. |
It is only applicable to sexual organism. | Applicable to both sexual as well as asexual organism. |
Does not consider fossil and extinct species. | This theory consider the extinct species and fossils. |
Both the concept of biological and evolutionary species aims to define the species, although they are distinct from each other in terms of definition, criteria and emphasis. Biological species concept focuses more on reproductive compatibility of the organism to define it as species while evolutionary emphasises on evolutionary history and lineage continuity. Evolutionary concept addresses most of the limitations of biological species concept like considering fossil, extinct species, asexual organisms and defining species as dynamic entities.
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