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.

What is Concept of Species?

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.

Also Read: How Many Species Are There On Earth And How Many In India

Types of Species

Species are broadly categorized into six concepts, these are as follows:

Biological Species Concept

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.

Nominalistic Species Concept

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

Typological Species Concept or Morphological Species Concept

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.

Ecological Species Concept

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

Phylogenetic Species Concept

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.

Evolutionary Species Concept

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

Extinction of Species

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.

Key Characteristics of Biological Species Concept

The key characteristics of biological species concepts are as follows:

• Reproductive community: Members of species recognise their members as potential mates with whom they mate and produce fertile offspring. They cannot mate with other species although they look similar.
• Ecological Unit: Members of a particular species are different from each other but as a whole they form a unit or a group which interact with other species in an environment.
• Genetic Unit: Species composed of a large inter-communicating gene pool which means it has the collection of alleles and traits which are flowing within the species through the process of mating and reproduction.

Disadvantages of Biological Species Concept

The limitation of biological species concept are as follows:

• Biological species concept does not focus on asexual organisms that produce offspring without sexual reproduction or interbreeding. Bacteria, fungi and protists reproduce asexually by the process of binary fission, budding and fragmentation. This makes it difficult for asexual organisms to be kept under the boundaries of species.
• This theory does not consider the allopatric population which are geographically isolated and cannot interbreed. Even if they are brought into contact, this theory will not be applicable as it relies on reproductive isolation.
• Biological species concept does not address the cases of hybridisation and introgression. Hybridisation occurs naturally or due to human activity caused due to introduction of non native species or due to habitat disturbance. Introgression is the process where genetic material transfers between species due to hybridisation.
• It only considers the living population and does not consider the extinct species and fossil records.

Also Read: Difference Between Bacteria And Fungi

Difference Between Biological Species Concept and Evolutionary Species Concept

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.