School of Studies in Zoology
Jiwaji University, Gwalior
Paper 401: Animal Taxonomy and Evolution
Topic:-SPECIES CONCEPT: DIFFERENT CONCEPTS
OF SPECIES
Dr. Hemant Samadhiya
CONTENTS
Introduction.
What is a species ?
Different concepts of species:
I. Historical concepts
Static concept of species
Dynamic concept of species
Typological concept
Nominalistic concept
II. Modern concepts
Evolutionary concept
Biological concept
Conclusion
References
INTRODUCTION
Defining and recognizing a species has been a controversial issue for a long time.
To determine the variation and the limitation between species many concepts have
been proposed .
When a taxonomist study a particular taxa, They must adopt a species concept and
provide a limitation to define a taxa.
Taxonomic classification was first proposed by Linnaeus. Hierarchy of categories is
the classification of organisms in a definite sequence of categories in a descending
order starting from kingdom.
The hierarchy includes seven obligate categories.
In order to make taxonomic position of species more precise, certain categories have
been added to this list and are termed as intermediate categories.
WHAT IS SPECIES?
The word „Species‟ has been derived from the Latin word meaning
„appearance‟ or „kind‟.
Linnaeus described species in terms of morphology.
Modern taxonomists put several changes on the basic concept of
species by considering several factors like genetic as well as
behavioral differences while describing species.
Species is a natural population of individuals or group of population
which resembles one another in all essential morphological and also
reproductive characters.
They are able to interbreed freely and produce fertile progenies.
DIFFERENT CONCEPTS OF SPECIES
A species is the unit of evolution and also is the unit of classification.
Only a species undergoes reproduction and modification process.
Various concepts regarding definition of a species have been given.
These are as follows :
Historical concepts:
Static concept
Typological concept
Nominalistic concept
Dynamic concept
Modern concepts :
Evolutionary concept
Biological concept
STATIC CONCEPT
The static concept of species was proposed by Linnaeus. According to
him „species is unchangeable‟.
There is no change in the character of species, the species of present
day are same as they were in the past and they will remain same in
future.
Linnaeus believed in the theory of special creation given by Father
Saurez, according to him, “all living organisms are created by God
and God gave the basic size and shape to all living organisms and are
present in the actual form.
DYNAMIC CONCEPT
This concept was put forward by Lamarck, by rejecting static concept
of species.
According to him, „species is always changeable‟. Changes always
occur in the character of species from one generation to another and
this process is known as evolution.
TYPOLOGICAL CONCEPT
It was proposed by Aristotle and Plato.
According to this concept „there is a definite type or pattern of
characters in each species of every living organism and all the
members of species show maximum resemblance with this pattern.
This includes :
1: Monotypic species: Having a single similar pattern or resemblance.
2: Polytypic species: In many species more than one type or pattern of
characters are present.
NOMINALISTIC CONCEPT
Nominalists deny the existence of “real” universals.
For them only individuals exist while species are abstractions created
by people.
This concept was popular in France during 18th century supported by
Buffon and Robinet.
According to this concept, “Nature produces individuals and nothing
more. Species have no actual existence in nature”.
Evolutionary concept rejects the nominalistic concept of species.
EVOLUTIONARY CONCEPT
An evolutionary species is a group of organisms that shares a common
ancestor.
In the process of evolution at some point of time members may
diverge from one another, when such a divergence becomes
sufficiently clear, the two populations are regarded as separate species.
Phenetic species concept: According to this concept, phenetic
similarity is all that matters in recognizing separate species.
Phenetic characters are all the observable or measurable characters
like behavioral, anatomy as well as morphological
MAYER’S CONCEPT
According to Mayer “all the members that can interbreed among
themselves and can produce fertile offspring's are the members of
same species”.
This definition of species is considered as incomplete because this is
applicable only to sexually reproducing living beings and as because
there are many organisms that have asexual mode of reproduction are
not satisfied.
The main character in determination of any species is interbreeding
but this character is not used in taxonomy.
When the species is determined on the basis of interbreeding then it is
known as biological species, like the humans which can interbreed
among themselves.
When the determination of species is based on other characters then it
is known as taxonomic species.
Like if there are same morphological characters between two
organisms, they belong to same taxonomic species i.e. one taxonomic
species but these cannot interbreed among themselves, so on the basis
of interbreeding they are two different biological species.
Example : Euglena sanguinea and Euglena laciniata.
FEW TERMS RELATED TO SPECIES
Ecotypes : Members of same species inhabiting different environment
and having some genetic variations are said to be ecotypes.
These members can interbreed among themselves but due to
geographical barriers they cannot interbreed.
E,g.: Crow {Corvus splendense} found in different regions are
ecotypes of one species.
Corvus splendense splendense - Indian crow
Corvus splendense insolence - Myanmar crow
Corvus splendense protegatus -Srilankan crow
Ecads: Members of same species having some genetic
variations due to environment are called Ecads.
Sibling species: Members of species which are
morphologically similar but reproductively isolated.
CONCLUSION
No one definition has satisfied all naturalists, yet every
naturalist knows vaguely what he means when he speaks of
a species.
According to biological concept of species it can be defined
as the members of population that can freely interbreed and
can produce fertile offspring's.
This concept is valid till date but is still considered as
incomplete.
REFERENCES
A textbook on Organic Evolution by P.D. Sharma.
www.sciencedirect.com
