The document discusses various concepts and definitions of species in biology. It begins by explaining how species have traditionally been viewed as essential, fixed units but are now understood to evolve and diversify over time. It then examines different species concepts, including the biological species concept which defines a species as a population that can interbreed but is reproductively isolated from other species. The document also discusses concepts like nominalism which questions whether species are "real" categories. It explores recognition, cohesion and evolutionary species concepts, and defines types of species such as cryptic, endemic and polytypic species. Finally, it examines intraspecific categories below the species level like subspecies.

1. KHAWAJA TAIMOOR SHAHID
Prof. Superior College
M.B.DiN

2. Introduction
• The species, like the cell and the organism, is one
of the most fundamental units in biology.
• Species become transformed through time. They
undergo speciation, giving rise to separate and
distinct lineages that diversify through time. It is
also a basic unit in classification.
• Essentialism or typology: Classification meant
discovering this essence, and defining groups on
the basis of supposedly ‘essential’ properties.
• Essentialism presupposes the reality of essences,
leading people to think in terms of stereotypes and
to screen out that which is unique or variable.

3. Nominalism and realism
• If a species gradually splits into two descendant species, for example,
there is no moment in time at which one can say that we now have
two species instead of one.
• classification as something arbitrary or conventional. It often takes the
form of claims that species are not ‘real’.
• The traditional claim of nominalists was that individuals are real, but
classes are not, and that species are classes and therefore not real.
Species Concepts and Definitions
• we speak of species concepts we generally mean something more
particular, for example the biological species concept, which is just
one example of an individualistic concept.
• These levels are called ‘categories’ and the groups that occupy the
levels are called ‘taxa’ (singular ‘taxon’). Thus the genus is a category,
and each and every group that has that rank, such as Homo, is a taxon.

4. The Biological Species Concept:
Species as Populations
• evolutionary biologists treats species as reproductively
isolated populations.
• A (biological) species is reproductively isolated from all
other species, and therefore it cannot interbreed with them.
• However, the biological species concept has many
difficulties, some imagined, others real. Reproductive
isolation between entire species is often confused with the
inability of any two organisms within a species to produce
offspring. The definition covers populations under natural
conditions: artificial crosses produced in the laboratory are
irrelevant.
• The biological species definition provides no criterion for
dividing up a single lineage into so-called chronospecies.

5. Recognition, Cohesion and
Evolutionary Species Concepts
• Recognition concept: The organisms are
supposed to share a ‘specific mate recognition
system’, or SMRS.
• species are reproductive populations, and on the
whole they are equivalent to biological species.
• However, there are two important differences.
• First, a population, in principle atleast, might vary
geographically in how mates are recognized.
• Second, a single lineage might evolve a different
SMRS.

6. Cohesion concept
• The cohesion concept emphasizes the point that
something does in fact hold species together.
• It has been suggested that something other than
sex might play this role.
Evolutionary concept
• populations as they exist at any given instant in
time: they are also lineages, and the fact that
they evolve is very important.

7. Cladistic species concepts
• the appropriate unit for the study of
relationships among lineages.
• This move would have many serious effects.
The number of species names would be vastly
increased. Also, human beings would not all
belong to the same species.
Prof. Taimoor Shahid
Superior College – M.B.Din

8. Species as Kinds, or Classes
• Folk taxonomy and common sense suggest that species taxa
are kinds of organisms. However, the biological species
concept does not treat them as kinds of organisms or for that
matter as kinds of anything.
• A university is made up of departments and professors, but
it is not a kind of department or a kind of professor.
Likewise when we say that somebody is a human being, we
do not mean that he or she is ‘a Homo sapiens’ but rather
that he or she is an organism-level component of Homo
sapiens. This may seem to contradict common usage, but it
really does not.
• Most people would consider a human sperm cell a part of
our species, even though it is not a human being.

9. Species as natural, or objective kinds
• The species category may likewise be interpreted as
such a natural kind. The biological species concept
picks out a kind of population about which laws of
nature may be formulated, at least in principle.
• Biological species, and likewise the genealogical units
(clades) that arise as a consequence of their speciating,
owe their properties to their history, rather than to laws
of nature.
• In evolutionary biology as it currently exists, species
taxa donot function as natural kinds. They function as
historical units.

10. Species as subjective kinds: phenetic and morphological
species concepts
• Natural kinds may be said to be objective classes, in the sense that their
definition is based upon laws of nature, laws that exist apart from
anybody’s opinion or personal judgement.
• However, not all kinds, or classes, have such an objective character,
and this is the main objection to various species concepts that treat taxa as
classes of similar objects.
• The phenetic species concept is based upon the idea of overall similarity
that was championed by the numerical pheneticist school of taxonomy.
• The morphological species concept treats species as classes of organisms
that are similar in terms of their anatomy and other so-called
morphological properties. It is an older and narrower form of phenetic
species concept,
• The genetical species concept treats species as classes of organisms with
similar genes.
• The physiological species concept treats species as kinds of organisms that
share the physiological capacity to mate and produce fertile offspring.

11. Kinds of Species: Polymorphic, Polytypic and Cryptic (Sibling)
• ‘Polymorphism’ means having many forms, and this term
is often used in the sense of genetic polymorphism, but it
also is sometimes used to refer to morphs within a species.
• A polytypic species is one that exists as discrete
populations that are somewhat divergent from one another.
Advocates of the biological species concept treat these as
single species, on the basis of their retained capacity to
interbreed.
• Cryptic or sibling species are biological species that are
hard for us human beings, including the experts, to tell
apart.
• Both ‘cryptic’ and ‘sibling’ are somewhat misleading
terms. To call them ‘cryptic species’ suggests that the
organisms, rather than the species are cryptic (hidden). To
call them ‘sibling species’ implies that they are one
another’s closest relatives, something that may or may not
be the case.

12. Concept of Species:
• Linnaeus (1735) conceived “species” as a unchangeable
unit. This monotypic or static concept prevailed till the
19th century.
• Later Lamarck (1809) and Darwin (1859) put forwarded
their evolutionary thoughts (polytypic or dynamic
concept). This concept states that the species undergo
modification in course of time, in order to adapt
themselves to the ecological niches and may gradually
form another species under favorable conditions.
• Dobzhansky (1937) has defined the species as “a group of
individuals which while passing through the ordeal of
evolution has been physiologically and genetically incom-
patible of inbreeding with other group of individuals”.
• Emerson (1941) proposed that “a species is that which
has evolved by reproductive isolation and a genetically
distinct group of natural population”.

13. • Mayr (1963) called a species as “groups of actually or
potentially interbreeding natural populations which are
morphologically distinct and reproductively isolated
from the neighbouring natural groups”.
• Simpson (1961) viewed species as “a lineage (an
ancestral-descendant sequence of populations) evolving
separately from others and with its own evolutionary
role and tendencies”.
• Christoffersen (1995) proposes that “a species is a
single lineage of ancestral-descendant sexual
populations genetically integrated by historically
contingent events of interbreeding”. This is the
ontological species concept.
Concept of Species:

14. Types of Species
• Allopatric species: The two or more related species that
have disjunct geographical ranges are called allopatric
species. Examples of such species are Indian lion.
• Sympatric species: Two or more species are said to be
sympatric when their geographical distributions overlap,
though they may segregate into different ecological niche.
Examples of this type are the fig-frog (Rana grylio) and the
gopher frog (R. areolata).
• Parapatric species: These are the species which have the
geographical ranges with a very narrow region of overlap.
Example of this type is the flightless Australian grass-
hoppers.
• Sibling species: Two or more than two closely related
species which are morphologically alike but behaviourally
or reproductively isolated from each other. Examples are
Drosophila persimilis and D. pseudoobscura.

15. Types of Species
• Cryptic species: The species which are alike on the basis of
observed features but are genetically and sexually they are
different are cryptic species. There is a confusion between the
terms sibling species and cryptic species. The cryptic species are
incapable of interbreeding but the sibling species can interbreed
and are incapable of producing fertile hybrids.
• Monotypic species: When a genus includes a single species but
does not include any subspecies, e.g., Vampyroteuthis, a vampire
squid which is a single monotypic genus and also contains a
single species, V. infernalis (monotypic species).
• Polytypic species: When a species contains two or more
subspecies, it is called polytypic species. Examples are tiger,
Panthera tigris which has several subspecies; such as—(i) Indian
tiger, Panthera tigris tigris, (ii) the Chinese tiger, P. t. amoyensis,
(iii) the Siberian tiger, P. t. altaica, (iv) the Javan tiger, P. t.
sondaica, etc.

16. Types of Species
• Endemic species: The species which are found in a
particular region, called endemic species. Usually the
species of oceanic islands which are found in a limited
geographic area are called endemic species. The Darwinian
finches are the endemic species of Galapagos Islands.
• Transient species: Species among contemporaneous
organisms, fossil or recent, called transient species (Imbrie,
1957). Blackwelder (1967) has defined that the species are
the ones existing contemporaneously, as a cross section of
the lineages of evolutionary species.
• Agamo species: Species are those which consist of
uniparental organisms. They may produce gametes but
fertilization does not take place. They reproduce by
obligatory parthenogenesis. In case of bees, wasps, rotifers
the haploid eggs develop into haploid individuals and the
haploid eggs are not fertilized by sperms.

17. Types of Species
• Panmictic species: Species in which a single
interbreeding population occurs (Blackwelder,
1967).
• Apomictic species: Species in which there is
mixing of gametes between different individuals.
• Incipient species: A natural population which are
about genetically isolated from the rest of
population of the parent species due to
geographical barrier but has not accomplished all
qualities for reproductive isolation from the parent
population.

18. Intraspecific Categories of Species:
• Subspecies: Linnaeus used the term “subspecies” when he
classified subgroups of man. He recognised four subgroups or
variations such as
– (i) the American-Indians (Homo sapiens americanus),
– (ii) the Europeans (Homo sapiens europaeus),
– (iii) the Orientals (Homo sapiens asiaticus) and
– (iv) the African Negroes (Homo sapiens afers).
• Subspecies is a deviation from the type of species.
• Early taxonomists applied the term ‘variety’ indiscriminately for
any variation in the population of a species. In the 19th century
the term subspecies replaced ‘variety’ and the term ‘variety’ is
obsolete today. Subspecies is actually a category below species.
• Wilson and Brown (1953) proposed the abolition of trinomial
nomenclature which is considered as subspecies concept. The
scientific name of the race (subspecies) of Indian lion is Panthera
leo persica, and the name of the African lion (race) is P. I. leo.

19. • Grant (1960) has defined the subspecies as “the
groups of interbreeding populations with some
morphological differences, combined with
geographical, ecological or physiological distinctions
which give it species-like distinctness”.
• With the establishment of polytypic concept
(Beckner, 1959), it is well accepted that some species
are distributed in different geographical areas and
form different local populations.
• It is widely accepted that genotypic variation within
allopatric species occurs. It is widely accepted that
these populations become different from each other
in morphology, biochemical or genotypic variations
that help to mark a taxonomic level sufficient to
designate them as subspecies.
Intraspecific Categories of Species:

20. Prof. Taimoor Shahid
Superior College M.B.Din
0306-0746125