Species concept
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About This Presentation
Species concept
evolution
Slide Content
University of education
LMC lahore
.Topic
Species concept
HAFIZ M WASEEM
LAHORE
LMC lahore
.Topic
Species concept
HAFIZ M WASEEM
LAHORE
Contents
.Definition
.Microtaxonomy
.History
.Species concept by scientists
.Definition
.Microtaxonomy
.History
.Species concept by scientists
.Species problem
.Chornospecies
.Types of species concept
.Criticism
.Metapopulution concept
.Causes of problema
.Solution for problem
. Conclusion
.
.Chornospecies
.Types of species concept
.Criticism
.Metapopulution concept
.Causes of problema
.Solution for problem
. Conclusion
.
Define
“Species are often defined as a group of individuals with similar
characteristics, where they can interbreed to produce fertile
offsprings.“
To differentiate between different types of living organisms, species
is used as the principal natural unit in biology.
Four most important concept of species are:
Species concept
species problem is the set of questions that arises
when biologists attempt to define what a species is. Such a definition
is called a species concept
There are at least 26 recognized species concepts.
“Species are often defined as a group of individuals with similar
characteristics, where they can interbreed to produce fertile
offsprings.“
To differentiate between different types of living organisms, species
is used as the principal natural unit in biology.
Four most important concept of species are:
Species concept
species problem is the set of questions that arises
when biologists attempt to define what a species is. Such a definition
is called a species concept
There are at least 26 recognized species concepts.
Microtaxonomy
A species concept that works well for sexually reproducing organisms such
as birds is useless for species that reproduce asexually, such as bacteria.
The scientific study of the species problem has been
called microtaxonomy.
One common, but sometimes difficult, question is how best to decide
which species an organism belongs to, because reproductively
isolated groups may not be readily recognizable, and cryptic
species may be present.
There is a continuum from reproductive isolation with no
interbreeding, to panmixis, unlimited interbreeding.
Populations can move forward or backwards along this continuum, at
any point meeting the criteria for one or another species concept, and
failing others.
Many of the debates on species touch on philosophical issues, such
as nominalism and realism, and on issues of language and cognition.
The current meaning of the phrase "species problem" is quite
different from what Charles Darwin and others meant by it during the
19th and early 20th centuries.
Species concept by Darwin
For Darwin, the species problem was the question of how new species
arose. Darwin was however one of the first people to question how well-
defined species are, given that they constantly change.
A species concept that works well for sexually reproducing organisms such
as birds is useless for species that reproduce asexually, such as bacteria.
The scientific study of the species problem has been
called microtaxonomy.
One common, but sometimes difficult, question is how best to decide
which species an organism belongs to, because reproductively
isolated groups may not be readily recognizable, and cryptic
species may be present.
There is a continuum from reproductive isolation with no
interbreeding, to panmixis, unlimited interbreeding.
Populations can move forward or backwards along this continuum, at
any point meeting the criteria for one or another species concept, and
failing others.
Many of the debates on species touch on philosophical issues, such
as nominalism and realism, and on issues of language and cognition.
The current meaning of the phrase "species problem" is quite
different from what Charles Darwin and others meant by it during the
19th and early 20th centuries.
Species concept by Darwin
For Darwin, the species problem was the question of how new species
arose. Darwin was however one of the first people to question how well-
defined species are, given that they constantly change.
The idea that an organism reproduces by giving birth to a similar
organism, or producing seeds that grow to a similar organism, goes
back to the earliest days of farming
. While people tended to think of this as a relatively stable process,
many thought that change was possible.
Species concept by John Ray
The term species was just used as a term for a sort or kind of
organism, until in 1686 John Ray introduced the biological concept
that species were distinguished by always producing the same
species, and this was fixed and permanent, though considerable
variation was possible within a species.
Species concept by Carolus linnaeus
Carolus Linnaeus (1707–1778) formalized the taxonomic rank of
species, and devised the two part naming system of binomial
nomenclature that we use today. However, this did not prevent
disagreements on the best way to identify species.
History
The history of definitions of the term "species"reveal that the seeds of
the modern species debate were alive and growing long before
Darwin.
The traditional view, which was developed by Cain, Mayr and Hull in
the mid-twentieth century, claims that until the ‘Origin of species’ by
Charles Darwin both philosophy and biology considered species as
invariable n
organism, or producing seeds that grow to a similar organism, goes
back to the earliest days of farming
. While people tended to think of this as a relatively stable process,
many thought that change was possible.
Species concept by John Ray
The term species was just used as a term for a sort or kind of
organism, until in 1686 John Ray introduced the biological concept
that species were distinguished by always producing the same
species, and this was fixed and permanent, though considerable
variation was possible within a species.
Species concept by Carolus linnaeus
Carolus Linnaeus (1707–1778) formalized the taxonomic rank of
species, and devised the two part naming system of binomial
nomenclature that we use today. However, this did not prevent
disagreements on the best way to identify species.
History
The history of definitions of the term "species"reveal that the seeds of
the modern species debate were alive and growing long before
Darwin.
The traditional view, which was developed by Cain, Mayr and Hull in
the mid-twentieth century, claims that until the ‘Origin of species’ by
Charles Darwin both philosophy and biology considered species as
invariable n
From Darwin to Myra
Charles Darwin's famous book On the Origin of Species (1859) offered
an explanation as to how species evolve, given enough time
. Although Darwin did not provide details on how species can split
into two, he viewed speciation as a gradual process.
If Darwin was correct, then, when new incipient species are forming,
there must be a period of time when they are not yet distinct enough
to be recognized as species. Darwin's theory suggested that there
was often not going to be an objective fact of the matter, on whether
there were one or
pecies problem.
In it, he wrote about how different investigators approach species
identification, and he characterized their approaches as species
concepts. He argued for what came to be called thebiological species
concept
, that a species consists of populations of organisms that can
reproduce with one another and that are reproductively isolated from
other populations, though he was not the first to define "species" on
the basis of reproductive compatibility
For example, Mayr discusses how Buffon proposed this kind of
definition of "species" in 1753. Theodosius Dobzhansky was a
contemporary of Mayr and the author of a classic book about the
evolutionary origins of reproductive barriers between species,
published a few years before Mayr's
Charles Darwin's famous book On the Origin of Species (1859) offered
an explanation as to how species evolve, given enough time
. Although Darwin did not provide details on how species can split
into two, he viewed speciation as a gradual process.
If Darwin was correct, then, when new incipient species are forming,
there must be a period of time when they are not yet distinct enough
to be recognized as species. Darwin's theory suggested that there
was often not going to be an objective fact of the matter, on whether
there were one or
pecies problem.
In it, he wrote about how different investigators approach species
identification, and he characterized their approaches as species
concepts. He argued for what came to be called thebiological species
concept
, that a species consists of populations of organisms that can
reproduce with one another and that are reproductively isolated from
other populations, though he was not the first to define "species" on
the basis of reproductive compatibility
For example, Mayr discusses how Buffon proposed this kind of
definition of "species" in 1753. Theodosius Dobzhansky was a
contemporary of Mayr and the author of a classic book about the
evolutionary origins of reproductive barriers between species,
published a few years before Mayr's
Many biologists credit Dobzhansky and Mayr jointly for emphasizing
reproductive isolation.
After Mayr's book, some two dozen species concepts were
introduced. Some, such as the Phylogenetic Species
Concept (PSC), were designed to be more useful than the BSC for
describing species. Many authors have professed to "solve" or
"dissolve" the species problem
Some have argued that the species problem is too multidimensional
to be "solved" by any one concept.
Since the 1990s, others have argued that concepts intended to help
describe species have not helped to resolve the species problem.
Although Mayr promoted the BSC for use in systematics, some
systematists have criticized it as not operational.
For others, the BSC is the preferred definition of species.
Many geneticists who work on speciation prefer the BSC because it
emphasizes the role of reproductive isolation.
It has been argued that the BSC is a natural consequence of the
effect of sexual reproduction on the dynamics of natural selection.
[
Biological species concept
The biological species concept defines a species as
members of populations that actually or potentially
interbreed in nature, not according to similarity of
reproductive isolation.
After Mayr's book, some two dozen species concepts were
introduced. Some, such as the Phylogenetic Species
Concept (PSC), were designed to be more useful than the BSC for
describing species. Many authors have professed to "solve" or
"dissolve" the species problem
Some have argued that the species problem is too multidimensional
to be "solved" by any one concept.
Since the 1990s, others have argued that concepts intended to help
describe species have not helped to resolve the species problem.
Although Mayr promoted the BSC for use in systematics, some
systematists have criticized it as not operational.
For others, the BSC is the preferred definition of species.
Many geneticists who work on speciation prefer the BSC because it
emphasizes the role of reproductive isolation.
It has been argued that the BSC is a natural consequence of the
effect of sexual reproduction on the dynamics of natural selection.
[
Biological species concept
The biological species concept defines a species as
members of populations that actually or potentially
interbreed in nature, not according to similarity of
appearance. Although appearance is helpful in identifying
species, it does not define species.
Appearance isn't everything
Organisms may appear to be alike and be different species. For
example, Western meadowlarks ( Sturnella neglecta) and Eastern
meadowlarks (Sturnella magna) look almost identical to one
another, yet do not interbreed with each other — thus, they are
separate species according to this definition.
The Western meadowlark (left) and the
Eastern meadowlark (right) appear to be
identical, and their ranges overlap, but
their distinct songs prevent
interbreeding.
Organisms may look different and yet be the
same species. For example, look at these
ants. You might think that they are distantly
related species. In fact, they are sisters—
two ants of the species Pheidole barbata,
fulfilling different roles in the same colony.
species, it does not define species.
Appearance isn't everything
Organisms may appear to be alike and be different species. For
example, Western meadowlarks ( Sturnella neglecta) and Eastern
meadowlarks (Sturnella magna) look almost identical to one
another, yet do not interbreed with each other — thus, they are
separate species according to this definition.
The Western meadowlark (left) and the
Eastern meadowlark (right) appear to be
identical, and their ranges overlap, but
their distinct songs prevent
interbreeding.
Organisms may look different and yet be the
same species. For example, look at these
ants. You might think that they are distantly
related species. In fact, they are sisters—
two ants of the species Pheidole barbata,
fulfilling different roles in the same colony.
Many characteristics can vary within a single species. For
example, the plant hydrangea may have pink "flowers" —
they're actually modified leaves — or blue "flowers." But that
doesn't mean that we should classify the two forms as
different species. In fact, you could cause a blue-"flowered"
plant to become a pink-"flowered" plant just by changing the
pH of the soil and the amount of aluminum taken up by the
plant.
Adding to the problem
We already pointed out two of the difficulties with the biological
species concept: what do you do with asexual organisms, and
what do you do with organisms that occasionally form hybrids
with one another? Other difficulties include:
What is meant by "potentially interbreeding?" If a population
of frogs were divided by a freeway, as shown below, that
prevented the two groups of frogs from interbreeding,
should we designate them as separate species? Probably not
— but how distantly separated do they have to be before we
draw the line?
example, the plant hydrangea may have pink "flowers" —
they're actually modified leaves — or blue "flowers." But that
doesn't mean that we should classify the two forms as
different species. In fact, you could cause a blue-"flowered"
plant to become a pink-"flowered" plant just by changing the
pH of the soil and the amount of aluminum taken up by the
plant.
Adding to the problem
We already pointed out two of the difficulties with the biological
species concept: what do you do with asexual organisms, and
what do you do with organisms that occasionally form hybrids
with one another? Other difficulties include:
What is meant by "potentially interbreeding?" If a population
of frogs were divided by a freeway, as shown below, that
prevented the two groups of frogs from interbreeding,
should we designate them as separate species? Probably not
— but how distantly separated do they have to be before we
draw the line?
Ring species are species with a geographic distribution that
forms a ring and overlaps at the ends. The many subspecies
of Ensatina salamanders in California exhibit subtle
morphological and genetic differences all along their range.
They all interbreed with their immediate neighbors with one
exception: where the extreme ends of the range overlap in
Southern California, E. klauberi and E. eschscholtzii do not
interbreed. So where do we mark the point of speciation?
forms a ring and overlaps at the ends. The many subspecies
of Ensatina salamanders in California exhibit subtle
morphological and genetic differences all along their range.
They all interbreed with their immediate neighbors with one
exception: where the extreme ends of the range overlap in
Southern California, E. klauberi and E. eschscholtzii do not
interbreed. So where do we mark the point of speciation?
Chronospecies are different stages in the same evolving
lineage that existed at different points in time. Obviously,
chronospecies present a problem for the biological species
concept — for example, it is not really possible (or very
meaningful!) to figure out whether a trilobite living 300
million years ago would have interbred with its ancestor
living 310 million years ago.
This trilobite lineage below evolved gradually over time:
Should we consider trilobite A as a separate species from
trilobite D, and if so, where should we divide the lineage into
separate species?
Species Concept: 4 Important Species Concept (With Criticism)
he following points highlight the four important species concept.
The important species concept are:
1. Typological or Essentialist Species Concept
2. Nominalistic Species Concept
3. Biological Species Concept
lineage that existed at different points in time. Obviously,
chronospecies present a problem for the biological species
concept — for example, it is not really possible (or very
meaningful!) to figure out whether a trilobite living 300
million years ago would have interbred with its ancestor
living 310 million years ago.
This trilobite lineage below evolved gradually over time:
Should we consider trilobite A as a separate species from
trilobite D, and if so, where should we divide the lineage into
separate species?
Species Concept: 4 Important Species Concept (With Criticism)
he following points highlight the four important species concept.
The important species concept are:
1. Typological or Essentialist Species Concept
2. Nominalistic Species Concept
3. Biological Species Concept
4. Evolutionary Species Concept.
1. Typological Species Concept:
According to this concept, there are a number of diversities on the surface
of the earth that exist as a limited number of universals or types
. These types do not bear any relationship to each other. The
universals or types are called species. Variation is considered as
trifling and irrelevant phenomenon.
This concept, was in the philosophies of Plato and Aristotle and was
the species concept of Linnaeus and his followers. Cain (1954, 1956)
regarded the above concept as the morpho-species concept. Another
group of scientists refer to this as essentialist species concept because
the members of a taxon or the species can be recognised by their
essential characters.
This is why essentialist ideology is also referred to as typology. Again
morpho-species or morphological species concept states that one
species can be segregated from another species by physical features
and can be recognised by their morphological features. This is also
called morphological species concept.
Criticisms:
Simpson (1961), Mayr (1969) and recent scientists have not
accepted the above concept totally though it has some positive
points:
1. Typological Species Concept:
According to this concept, there are a number of diversities on the surface
of the earth that exist as a limited number of universals or types
. These types do not bear any relationship to each other. The
universals or types are called species. Variation is considered as
trifling and irrelevant phenomenon.
This concept, was in the philosophies of Plato and Aristotle and was
the species concept of Linnaeus and his followers. Cain (1954, 1956)
regarded the above concept as the morpho-species concept. Another
group of scientists refer to this as essentialist species concept because
the members of a taxon or the species can be recognised by their
essential characters.
This is why essentialist ideology is also referred to as typology. Again
morpho-species or morphological species concept states that one
species can be segregated from another species by physical features
and can be recognised by their morphological features. This is also
called morphological species concept.
Criticisms:
Simpson (1961), Mayr (1969) and recent scientists have not
accepted the above concept totally though it has some positive
points:
(i) Due to several phenomena such as sexual dimorphism, polymorphism,
and age differences, the same species develop strikingly morphological
differences.
(ii) This concept is not applicable in case of sibling species because sibling
species are alike but belong to different species.
2. Nominalistic Species Concept:
Occan, the proponent of this concept and his followers (Buffon,
Bessey, Lamarck, etc.) believed that only individuals exist but do not
believe in the existence of species.
Species are man’s own creations and have no actual existence in
nature. They are mental concept and nothing more. Therefore, such
mental concept (i.e., species) of man has no value. This concept was
popular in France in 18
th
century and still now is used among some
botanists.
Criticisms:
Simpson (1961), Rollins (1965) and Mayr (1969) stated that no biologists
can agree with the idea that man cannot produce species and it is the
established fact that the species are the products of evolution.
3. Biological Species Concept:
Due to some incompleteness in the above mentioned concepts and
continuous pressure from the naturalists, a new concept the biological
species concept emerged in the middle of 18 century. The concept took a
number of years to get its foot in the soil of biology.
and age differences, the same species develop strikingly morphological
differences.
(ii) This concept is not applicable in case of sibling species because sibling
species are alike but belong to different species.
2. Nominalistic Species Concept:
Occan, the proponent of this concept and his followers (Buffon,
Bessey, Lamarck, etc.) believed that only individuals exist but do not
believe in the existence of species.
Species are man’s own creations and have no actual existence in
nature. They are mental concept and nothing more. Therefore, such
mental concept (i.e., species) of man has no value. This concept was
popular in France in 18
th
century and still now is used among some
botanists.
Criticisms:
Simpson (1961), Rollins (1965) and Mayr (1969) stated that no biologists
can agree with the idea that man cannot produce species and it is the
established fact that the species are the products of evolution.
3. Biological Species Concept:
Due to some incompleteness in the above mentioned concepts and
continuous pressure from the naturalists, a new concept the biological
species concept emerged in the middle of 18 century. The concept took a
number of years to get its foot in the soil of biology.
K. Jordan (1905) first gave the definition of biological species concept.
Later Mayr proposed the biological species concept in 1940, 1942, 1949.
According to this concept, “a species is a group of interbreeding
natural population that is reproductively isolated from other
such groups”. Mayr explained that a species has three following
properties.
These are:
1. Reproductive community:
The individuals of a species seek each other as potential mates for the
purpose of reproduction and the members form a reproductive community.
2. Ecological unit:
The members of a species differ each other for many features but all
members together form a unit, interact as a unit with other species in any
environment.
3. Genetical unit:
The members freely interbreed consisting of an intercommunicating gene
pool, whereas the individual is merely a temporary vessel holding a small
portion of the contents of gene pool.
This definition of biological species concept has accepted by Dobzhansky
(1951) and Hanson (1981) especially for two reasons— gene pool and
reproductive isolation.
Dobzhansky, Ayala, Stebbins and Valentine (1977), have postulated more or
less same definition. According to them, a species as a single or more
Mendelian populations between which the gene exchange is limited or
prevented by reproductive isolating mechanisms.
Later Mayr proposed the biological species concept in 1940, 1942, 1949.
According to this concept, “a species is a group of interbreeding
natural population that is reproductively isolated from other
such groups”. Mayr explained that a species has three following
properties.
These are:
1. Reproductive community:
The individuals of a species seek each other as potential mates for the
purpose of reproduction and the members form a reproductive community.
2. Ecological unit:
The members of a species differ each other for many features but all
members together form a unit, interact as a unit with other species in any
environment.
3. Genetical unit:
The members freely interbreed consisting of an intercommunicating gene
pool, whereas the individual is merely a temporary vessel holding a small
portion of the contents of gene pool.
This definition of biological species concept has accepted by Dobzhansky
(1951) and Hanson (1981) especially for two reasons— gene pool and
reproductive isolation.
Dobzhansky, Ayala, Stebbins and Valentine (1977), have postulated more or
less same definition. According to them, a species as a single or more
Mendelian populations between which the gene exchange is limited or
prevented by reproductive isolating mechanisms.
Most modern taxonomists and evolutionists consider the biological species
concept as the widely accepted species concept because the maximum
workers apply this concept during their work. This concept has no fixity,
and always changeable and has the potentiality for modifications required
by the evolution.
Paterson (1985) has proposed a definition which can overcome some
defects present in the biological species concept. According to him
, “a species is a population of biparental organisms, the members
of which share a common fertilization system”
. Mayr (1988) has remarked that Paterson’s species concept is not error-
free and is based on the misinterpretation of the biological species concept.
Though Mayr’s biological species concept is widely accepted to
the zoologists but the- shortcomings of the concept are criticised
by the evolutionists when applied to certain groups:
(i) Lack of information:
Due to lack of proper information systematists face some problems when
applied to some cases.
(a) The morphological differences are observed due to sexual dimorphism,
age differences and genetical polymorphism and individual variation can be
unmasked through the study of life history and through the population
analysis. The taxonomists mostly work on preserved museum specimens.
So reproductive isolation is not verified in the preserved specimens. Again
biological species concept is not applicable in fossil specimens.
(b) The closely related two populations live in a continuous area but show
preferences for different habitats. In this case, two populations fail to
concept as the widely accepted species concept because the maximum
workers apply this concept during their work. This concept has no fixity,
and always changeable and has the potentiality for modifications required
by the evolution.
Paterson (1985) has proposed a definition which can overcome some
defects present in the biological species concept. According to him
, “a species is a population of biparental organisms, the members
of which share a common fertilization system”
. Mayr (1988) has remarked that Paterson’s species concept is not error-
free and is based on the misinterpretation of the biological species concept.
Though Mayr’s biological species concept is widely accepted to
the zoologists but the- shortcomings of the concept are criticised
by the evolutionists when applied to certain groups:
(i) Lack of information:
Due to lack of proper information systematists face some problems when
applied to some cases.
(a) The morphological differences are observed due to sexual dimorphism,
age differences and genetical polymorphism and individual variation can be
unmasked through the study of life history and through the population
analysis. The taxonomists mostly work on preserved museum specimens.
So reproductive isolation is not verified in the preserved specimens. Again
biological species concept is not applicable in fossil specimens.
(b) The closely related two populations live in a continuous area but show
preferences for different habitats. In this case, two populations fail to
interbreed due to living in different habitats. So it is difficult to apply the
biological species concept on these populations because these populations
are either distinct species or failure of interbreeding due to living in
different habitat.
An example of drongo birds is recorded in central Africa. Species A,
Dicrurus ludwigii are found in the evergreen rainy forest areas and species
B, D. adsimilis are found in the open grassy land areas. They live in two
ecological niches with a distance of 50 m apart and do not interbreed.
(ii) Apomictic or asexual groups:
Biological species concept is not applicable in apomictic species (i.e.,
asexually reproducing groups) that do not fulfil interbreeding criterion
which is the most important characteristic feature in biological species
concept. Apomictic groups show uniparental reproduction by
parthenogenesis, apomixes and budding, etc.
Uniparental reproduction is seen in lower invertebrates and lower
vertebrates. The descendents of apomictic groups are termed agamospecies
or binoms, paraspecies but Ghiselin (1987), Mayr (1988a) stated that these
are not considered as ‘species’.
To solve this dilemma, Simpson (1961), Mayr (1963, 1969) and M.J.D.
White (1978) discussed the problem on the basis of discussion of Dougherty
(1955) and Stebbins (1966).
Attempts to define agamospecies or asexual species with or without using
the word population have not been successful. There are well defined
morphological discontinuity among the uniparentally reproductive
biological species concept on these populations because these populations
are either distinct species or failure of interbreeding due to living in
different habitat.
An example of drongo birds is recorded in central Africa. Species A,
Dicrurus ludwigii are found in the evergreen rainy forest areas and species
B, D. adsimilis are found in the open grassy land areas. They live in two
ecological niches with a distance of 50 m apart and do not interbreed.
(ii) Apomictic or asexual groups:
Biological species concept is not applicable in apomictic species (i.e.,
asexually reproducing groups) that do not fulfil interbreeding criterion
which is the most important characteristic feature in biological species
concept. Apomictic groups show uniparental reproduction by
parthenogenesis, apomixes and budding, etc.
Uniparental reproduction is seen in lower invertebrates and lower
vertebrates. The descendents of apomictic groups are termed agamospecies
or binoms, paraspecies but Ghiselin (1987), Mayr (1988a) stated that these
are not considered as ‘species’.
To solve this dilemma, Simpson (1961), Mayr (1963, 1969) and M.J.D.
White (1978) discussed the problem on the basis of discussion of Dougherty
(1955) and Stebbins (1966).
Attempts to define agamospecies or asexual species with or without using
the word population have not been successful. There are well defined
morphological discontinuity among the uniparentally reproductive
organisms. These discontinuities are produced by natural selection among
the various mutants which occur in asexual clones.
Sibling or Cryptic species:
Biological species concept is not applicable in sibling or cryptic species
because members of sibling or cryptic species are all alike, not separated
morphologically but reproductively isolated populations.
Incompleteness of speciation:
Evolution is a gradual and continuous process. To attain a new species,
especially three attributes are necessary, such as reproductive isolation,
ecological difference and morphological differentiation. There are many
species which represents an incomplete stage during speciation. To apply
the biological species concept in these cases becomes difficult.
Hybridization:
According to biological species concept, two good species fail to interbreed.
If the reproduction isolation breaks down, the two good species interbreed
and produce fertile hybrid.
4. Evolutionary Species Concept:
Not all taxonomists specially palaeontologists are not satisfied with the
biological species concept. They preferred a definition of species which are
related to the evolution.
Simpson (1961) has proposed a definition with many modifications that
is “an evolutionary species is a lineage (an ancestral- descendant
sequence of populations) evolving separately from others and
with its own unitary evolutionary role and tendencies”.
the various mutants which occur in asexual clones.
Sibling or Cryptic species:
Biological species concept is not applicable in sibling or cryptic species
because members of sibling or cryptic species are all alike, not separated
morphologically but reproductively isolated populations.
Incompleteness of speciation:
Evolution is a gradual and continuous process. To attain a new species,
especially three attributes are necessary, such as reproductive isolation,
ecological difference and morphological differentiation. There are many
species which represents an incomplete stage during speciation. To apply
the biological species concept in these cases becomes difficult.
Hybridization:
According to biological species concept, two good species fail to interbreed.
If the reproduction isolation breaks down, the two good species interbreed
and produce fertile hybrid.
4. Evolutionary Species Concept:
Not all taxonomists specially palaeontologists are not satisfied with the
biological species concept. They preferred a definition of species which are
related to the evolution.
Simpson (1961) has proposed a definition with many modifications that
is “an evolutionary species is a lineage (an ancestral- descendant
sequence of populations) evolving separately from others and
with its own unitary evolutionary role and tendencies”.
Simpson has stated that the above definition not only is consistent with
biological or genetical concept of species but it helps to clarify and to
remove some limitations of the biological species concept. Mayr (1982) has
stated that the above definition is related to the phyletic lineage, not
indicates a species concept.
Christoffersen (1995) proposed the ontological species concept that is “a
species is a single lineage of ancestral descendant sexual populations
genetically integrated by historically contingent events of interbreeding”.
This definition of Christoffersen has given stress on the interbreeding
nature of a species.
The flaws of the biological species concept had led the palaeontologists to
formulate the evolutionary species concept.
1. Simpson (in 1961) had defined it as “an evolutionary species is a
lineage (an ancestral- descendant sequence of populations) evolving
separately from others and with its own unitary evolutionary role and
tendencies”.
2. Wiley (in 1978) had provided a revised definition of the evolutionary
species concept. He stated that “an evolutionary species are a single
lineage of ancestral-descendant population which draws its identity
from other such lineages and has its own evolutionary tendencies
and historical fate”.
Types of species
Following are the different types of species:
biological or genetical concept of species but it helps to clarify and to
remove some limitations of the biological species concept. Mayr (1982) has
stated that the above definition is related to the phyletic lineage, not
indicates a species concept.
Christoffersen (1995) proposed the ontological species concept that is “a
species is a single lineage of ancestral descendant sexual populations
genetically integrated by historically contingent events of interbreeding”.
This definition of Christoffersen has given stress on the interbreeding
nature of a species.
The flaws of the biological species concept had led the palaeontologists to
formulate the evolutionary species concept.
1. Simpson (in 1961) had defined it as “an evolutionary species is a
lineage (an ancestral- descendant sequence of populations) evolving
separately from others and with its own unitary evolutionary role and
tendencies”.
2. Wiley (in 1978) had provided a revised definition of the evolutionary
species concept. He stated that “an evolutionary species are a single
lineage of ancestral-descendant population which draws its identity
from other such lineages and has its own evolutionary tendencies
and historical fate”.
Types of species
Following are the different types of species:
1 Taxonomic Species
It includes a group of morphologically similar organisms.
2 Microspecies
The population is obtained from a single parent.
3 Biological Species
It includes the population that involves sexually reproducing individuals.
4 Evolutionary Species
It is a combination of sexually reproducing organisms, phyletic lineages and
uniparental organisms.
5 Successional Species
It includes phyletic lineages.
Genetic species concept
The genetic species concept states that all the organisms are capable of
inheriting traits from each other through a common gene pool.
Biodiversity
Biodiversity is divided into three different types:
Genetic biodiversity
Species biodiversity
Ecosystem biodiversity
It includes a group of morphologically similar organisms.
2 Microspecies
The population is obtained from a single parent.
3 Biological Species
It includes the population that involves sexually reproducing individuals.
4 Evolutionary Species
It is a combination of sexually reproducing organisms, phyletic lineages and
uniparental organisms.
5 Successional Species
It includes phyletic lineages.
Genetic species concept
The genetic species concept states that all the organisms are capable of
inheriting traits from each other through a common gene pool.
Biodiversity
Biodiversity is divided into three different types:
Genetic biodiversity
Species biodiversity
Ecosystem biodiversity
phylogenetic species concept
Phylogenetic species concept states that a few organisms have descended
from a common ancestor and possess a combination of certain derived
traits.
Who proposed the concept of species
The concept of species was proposed by a zoologist Mayr in the year
1942.
Modern species concept
an alternative definition, was published by George Gaylord Simpson
another leader of the Modern Synthesis
However, alternative species concepts did not really begin to
proliferate until the 1970s, starting with a paper by Sokal and Crovello
which proposed a phenetic species concept.
By the late 1990s, literally dozens of alternatives had been proposed.
Mayden for example, identified 24 named species concepts, including
the now-familiar biological, phenetic, evolutionary, ecological, and
phylogenetic (three versions) concepts and 16 others.
For the present discussion, the important thing to recognize is that
different contemporary species concepts are based, in part, on
different biological properties.
Phylogenetic species concept states that a few organisms have descended
from a common ancestor and possess a combination of certain derived
traits.
Who proposed the concept of species
The concept of species was proposed by a zoologist Mayr in the year
1942.
Modern species concept
an alternative definition, was published by George Gaylord Simpson
another leader of the Modern Synthesis
However, alternative species concepts did not really begin to
proliferate until the 1970s, starting with a paper by Sokal and Crovello
which proposed a phenetic species concept.
By the late 1990s, literally dozens of alternatives had been proposed.
Mayden for example, identified 24 named species concepts, including
the now-familiar biological, phenetic, evolutionary, ecological, and
phylogenetic (three versions) concepts and 16 others.
For the present discussion, the important thing to recognize is that
different contemporary species concepts are based, in part, on
different biological properties.
For example, the biological species concept emphasizes the property
of reproductive isolation the ecological species concept emphasizes
occupation of a distinct niche or adaptive zone one version of the
phylogenetic species concept emphasizes diagnosability and
another, monophyly
For a more extensive list of properties that form the basis of
alternative species concepts,
The existence of alternative. and at least partially incompatible,
definitions of the species category, hereafter referred to as the
“species problem,” creates difficulties given that species are used as
basic units ofcomparison in diverse types of studies.
On the one hand, species taxa recognized according to different
species concepts often will not be comparable to one another with
regard to the biological properties they possess.
On the other hand, a study that uses species taxa based on a single
species concept may yield very different results from one that uses
species taxa based on a different species concept.
The existence of diverse species concepts is not altogether
unexpected, because different concepts are based on properties that
are of greatest interest to different subgroups of biologists
. For example, biologists who study hybrid zones tend to emphasize
reproductive barriers, whereas systematists tend to emphasize
of reproductive isolation the ecological species concept emphasizes
occupation of a distinct niche or adaptive zone one version of the
phylogenetic species concept emphasizes diagnosability and
another, monophyly
For a more extensive list of properties that form the basis of
alternative species concepts,
The existence of alternative. and at least partially incompatible,
definitions of the species category, hereafter referred to as the
“species problem,” creates difficulties given that species are used as
basic units ofcomparison in diverse types of studies.
On the one hand, species taxa recognized according to different
species concepts often will not be comparable to one another with
regard to the biological properties they possess.
On the other hand, a study that uses species taxa based on a single
species concept may yield very different results from one that uses
species taxa based on a different species concept.
The existence of diverse species concepts is not altogether
unexpected, because different concepts are based on properties that
are of greatest interest to different subgroups of biologists
. For example, biologists who study hybrid zones tend to emphasize
reproductive barriers, whereas systematists tend to emphasize
diagnosability and monophyly, and ecologists tend to emphasize
niche differences.
The Metapopulation Lineage Concept of Species
This general concept of species originated at least as early as the
beginning of the 20th century [Mayr cited papers by Jordan and Poulton as
early examples], but it became well established during the period of the
Modern Evolutionary Synthesis , through the writings of the great leaders of
that movement, including Sewall Wright, Theodosius Dobzhansky, George
Gaylord Simpson, and particularly Ernst Mayr.
. The equation of species with metapopulations or gene pools is
evident in a number of species definitions from the period of the
Modern Synthesis, including those proposed by several of the most
influential contributors to that movement. Thus, according to Sewall
Wright
" species are groups within which all subdivisions interbreed
sufficiently freely to form intergrading populations wherever
they come in contact, but between which there is so little
interbreeding that suchpopulations are not found.”
Similarly, according to Theodosius Dobzhansky
“The biological species is the largest and most inclusive
Mendelian population” (a “Mendelian population is a
niche differences.
The Metapopulation Lineage Concept of Species
This general concept of species originated at least as early as the
beginning of the 20th century [Mayr cited papers by Jordan and Poulton as
early examples], but it became well established during the period of the
Modern Evolutionary Synthesis , through the writings of the great leaders of
that movement, including Sewall Wright, Theodosius Dobzhansky, George
Gaylord Simpson, and particularly Ernst Mayr.
. The equation of species with metapopulations or gene pools is
evident in a number of species definitions from the period of the
Modern Synthesis, including those proposed by several of the most
influential contributors to that movement. Thus, according to Sewall
Wright
" species are groups within which all subdivisions interbreed
sufficiently freely to form intergrading populations wherever
they come in contact, but between which there is so little
interbreeding that suchpopulations are not found.”
Similarly, according to Theodosius Dobzhansky
“The biological species is the largest and most inclusive
Mendelian population” (a “Mendelian population is a
reproductive community of sexual and crossfertilizing
individuals which share in a common gene pool”).
And finally, according to Ernst Mayr
Species are groups of actually or potentially interbreeding
natural populations, which are reproductively isolated from
other such groups.”
All three of these definitions equate species with metapopulations
(sets of connected subpopulations, maximally inclusive populations),
and all of them suggest that the limits of species as metapopulations
are set in one way or another by the limits of interbreeding (which
requires not only mating but also the production of viable and fertile
offspring), thus implying sexual reproduction.
For cases involving purely asexual reproduction, there are two possibilities
regarding species.
1 one possibility is that purely asexual organisms do not form species
2 The other possibility is there are processes other than the exchange of
genetic material, such as natural selection, that determine the limits of
species in purely asexual organisms Both of these views are consistent
with the equation of species with metapopulations.
Either asexual organisms do not form metapopulations, and therefore
they do not form species, or they do form metapopulations (as the
individuals which share in a common gene pool”).
And finally, according to Ernst Mayr
Species are groups of actually or potentially interbreeding
natural populations, which are reproductively isolated from
other such groups.”
All three of these definitions equate species with metapopulations
(sets of connected subpopulations, maximally inclusive populations),
and all of them suggest that the limits of species as metapopulations
are set in one way or another by the limits of interbreeding (which
requires not only mating but also the production of viable and fertile
offspring), thus implying sexual reproduction.
For cases involving purely asexual reproduction, there are two possibilities
regarding species.
1 one possibility is that purely asexual organisms do not form species
2 The other possibility is there are processes other than the exchange of
genetic material, such as natural selection, that determine the limits of
species in purely asexual organisms Both of these views are consistent
with the equation of species with metapopulations.
Either asexual organisms do not form metapopulations, and therefore
they do not form species, or they do form metapopulations (as the
result of some process or processes other than interbreeding), and
therefore they also form species.
Gaylord Simpson
species is a lineage (an ancestral-descendant sequence of
populations) evolving separately from others and with its own
unitary evolutionary role and tendencies.”
Similarly, according to Leigh Van Valen
“A species is a lineage (or a closely related set of lineages)
which occupies an adaptive zone minimally different from that of
any other lineage in its range and which evolves separately from
all lineages outside its range.
” The reason definitions that characterize species as lineages can be
considered to represent the same general species concept as those that
characterize species as (meta)populations is there is a close relationship
between populations and lineages at the same level of biological
organization
therefore they also form species.
Gaylord Simpson
species is a lineage (an ancestral-descendant sequence of
populations) evolving separately from others and with its own
unitary evolutionary role and tendencies.”
Similarly, according to Leigh Van Valen
“A species is a lineage (or a closely related set of lineages)
which occupies an adaptive zone minimally different from that of
any other lineage in its range and which evolves separately from
all lineages outside its range.
” The reason definitions that characterize species as lineages can be
considered to represent the same general species concept as those that
characterize species as (meta)populations is there is a close relationship
between populations and lineages at the same level of biological
organization
the one hand, populations can be considered to extend through time, in
which case a population is equivalent to a lineage.
The Cause of the Species Problem
Reason emphasis on different contingent properties leads to
incompatible species definitions is that those properties arise at
which case a population is equivalent to a lineage.
The Cause of the Species Problem
Reason emphasis on different contingent properties leads to
incompatible species definitions is that those properties arise at
different times during the process of separation and divergence
among metapopulation lineages (i.e., speciation).
Lineage separation and divergence can be conceptualized in terms
of a few general evolutionary processes: mutation, natural selection,
migration (or the lack thereof), and genetic drift.
In contrast, the properties affected by those processes are highly
diverse. They may be genetic or phenotypic, qualitative or
quantitative, selectively advantageous, disadvantageous, or neutral,
and they may involve many different aspects of biology, including
genetics, development, morphology, physiology, and behavior
The problem is that each alternative species definition adopts a
different one of these properties as a defining or necessary property
of species.
This is the reason that the alternative species definitions, despite their
general agreement regarding the conceptualization of species as
metapopulation lineages, imply different conclusions concerning
which lineages deserve to be recognized as species.
The highly simplified diagram is represents the process of
metapopulation lineage divergence.
The progressive darkening and lightening of the daughter lineages
represent their increasing divergence through time, and the
numbered lines represent the times at which they acquire different
properties relative to one another
among metapopulation lineages (i.e., speciation).
Lineage separation and divergence can be conceptualized in terms
of a few general evolutionary processes: mutation, natural selection,
migration (or the lack thereof), and genetic drift.
In contrast, the properties affected by those processes are highly
diverse. They may be genetic or phenotypic, qualitative or
quantitative, selectively advantageous, disadvantageous, or neutral,
and they may involve many different aspects of biology, including
genetics, development, morphology, physiology, and behavior
The problem is that each alternative species definition adopts a
different one of these properties as a defining or necessary property
of species.
This is the reason that the alternative species definitions, despite their
general agreement regarding the conceptualization of species as
metapopulation lineages, imply different conclusions concerning
which lineages deserve to be recognized as species.
The highly simplified diagram is represents the process of
metapopulation lineage divergence.
The progressive darkening and lightening of the daughter lineages
represent their increasing divergence through time, and the
numbered lines represent the times at which they acquire different
properties relative to one another
, for example, when they become phenetically distinguishable, diagnosable,
reciprocally monophyletic, reproductively incompatible, ecologically distinct,
A Solution to the Species Problem
Both the species problem itself and the discrepancy between the
general theoretical significance commonly attributed to species and
the treatment of species in taxonomic practice can be solved by
making a simple yet fundamental shift in the way species are
conceptualized
reciprocally monophyletic, reproductively incompatible, ecologically distinct,
A Solution to the Species Problem
Both the species problem itself and the discrepancy between the
general theoretical significance commonly attributed to species and
the treatment of species in taxonomic practice can be solved by
making a simple yet fundamental shift in the way species are
conceptualized
This shift is highly consistent with the general concept of species that
became established during the Modern Evolutionary Synthesis and
for which Ernst Mayr was arguably the most important spokesman.
It also represents the more complete acceptance of Mayr's
proposition that the species is one of the fundamental categories of
biological organization
. The proposed solution retains the element common to all
contemporary concepts of species, and it eliminates the conflicts
between those rival concepts without denying the importance of the
properties that underlie their obvious differences.
The proposal has two components.
First, it retains the element common to all contemporary concepts
and definitions of species by adopting the general concept of species
as separately evolving metapopulation lineages
. Second, it eliminates the conflicts among rival concepts by treating
this property, existence as a separately evolving metapopulation
lineage, as the only necessary property of species.
In other words, all of the other properties that have previously been
treated as necessary properties of species, which created
incompatibilities among alternative species concepts, are
reinterpreted as no longer being defining properties of the species
category
. Thus, under a general and unified species concept, all of the
properties that have been considered important by previous authors
remain important for determining the numbers and boundaries of
became established during the Modern Evolutionary Synthesis and
for which Ernst Mayr was arguably the most important spokesman.
It also represents the more complete acceptance of Mayr's
proposition that the species is one of the fundamental categories of
biological organization
. The proposed solution retains the element common to all
contemporary concepts of species, and it eliminates the conflicts
between those rival concepts without denying the importance of the
properties that underlie their obvious differences.
The proposal has two components.
First, it retains the element common to all contemporary concepts
and definitions of species by adopting the general concept of species
as separately evolving metapopulation lineages
. Second, it eliminates the conflicts among rival concepts by treating
this property, existence as a separately evolving metapopulation
lineage, as the only necessary property of species.
In other words, all of the other properties that have previously been
treated as necessary properties of species, which created
incompatibilities among alternative species concepts, are
reinterpreted as no longer being defining properties of the species
category
. Thus, under a general and unified species concept, all of the
properties that have been considered important by previous authors
remain important for determining the numbers and boundaries of
species, and they take on new importance in identifying those
species most relevant to addressing particular questions
. The main difference is they are no longer treated as necessary
properties of species.
Another beneficial consequence of this proposal is that it removes the
inconsistency between the proposition that the species is a fundamental
Ernst Mayr and the Modern Concept of Species
Mayr's choice of the adjective “biological” as in the terms “biological
species definition” and “biological species concept” has sometimes been
criticized for being overly general thus raising the suspicion that it was
chosen more for its rhetorical value than for its descriptive accuracy.
However, an examination of Mayr's writings on species reveals he had
good reason for selecting this adjective.
According to Mayr
“This species concept is called biological not because it deals with
biological taxa, but because the definition is biological
. It utilizes criteria that are meaningless as far as the inanimate world
is concerned.” The important idea for Mayr was that earlier concepts
of species were based on properties, such as degree of difference,
that could be applied just as easily to inanimate objects as to living
things. Linnaeus
, for example, recognized species not only of plants and animals but
also of rocks and minerals. In contrast, a truly biological concept of
species most relevant to addressing particular questions
. The main difference is they are no longer treated as necessary
properties of species.
Another beneficial consequence of this proposal is that it removes the
inconsistency between the proposition that the species is a fundamental
Ernst Mayr and the Modern Concept of Species
Mayr's choice of the adjective “biological” as in the terms “biological
species definition” and “biological species concept” has sometimes been
criticized for being overly general thus raising the suspicion that it was
chosen more for its rhetorical value than for its descriptive accuracy.
However, an examination of Mayr's writings on species reveals he had
good reason for selecting this adjective.
According to Mayr
“This species concept is called biological not because it deals with
biological taxa, but because the definition is biological
. It utilizes criteria that are meaningless as far as the inanimate world
is concerned.” The important idea for Mayr was that earlier concepts
of species were based on properties, such as degree of difference,
that could be applied just as easily to inanimate objects as to living
things. Linnaeus
, for example, recognized species not only of plants and animals but
also of rocks and minerals. In contrast, a truly biological concept of
species must be based on properties that are unique to biological
systems, properties such as reproduction and interbreeding.
Thus, in Systematics and the Origin of Species Mayr referred to the
general concept as “the new species concept,” and he referred to his
proposed definition as “a biological species definition” (not “the
biological species definition”) . He also called it “a practical species
definition,”
Mayr stated, “A study of all of the species definitions published in
recent years indicates that they are based on three theoretical
concepts, neither more nor less”
He called these three concepts “the typological species concept”
(used to refer to older species concepts that could be applied to
inanimate objects), “the nondimensional species concept” (for the
concept adopted by naturalists working at a single time and place),
and the “interbreeding-population concept” (for the concept he
advocated)
. Conclusion
Ernst Mayr is almost certainly the greatest of all biologists in terms of
his contributions to the development and acceptance of modern
views on species
. However, with regard to theoretical advances and their practical
consequences, his most important contribution in this area was not his
widely adopted definition of species but rather the major role he played
systems, properties such as reproduction and interbreeding.
Thus, in Systematics and the Origin of Species Mayr referred to the
general concept as “the new species concept,” and he referred to his
proposed definition as “a biological species definition” (not “the
biological species definition”) . He also called it “a practical species
definition,”
Mayr stated, “A study of all of the species definitions published in
recent years indicates that they are based on three theoretical
concepts, neither more nor less”
He called these three concepts “the typological species concept”
(used to refer to older species concepts that could be applied to
inanimate objects), “the nondimensional species concept” (for the
concept adopted by naturalists working at a single time and place),
and the “interbreeding-population concept” (for the concept he
advocated)
. Conclusion
Ernst Mayr is almost certainly the greatest of all biologists in terms of
his contributions to the development and acceptance of modern
views on species
. However, with regard to theoretical advances and their practical
consequences, his most important contribution in this area was not his
widely adopted definition of species but rather the major role he played
in the development and advocacy of the general metapopulation lineage
concept of species.
This contribution had tremendous significance both for systematics in
particular and for biology in general
. It represented a fundamental shift in the conceptualization of the
species category that resulted in a uniquely biological concept of
species and changed the species category from a more-or-less
arbitrary rank in the hierarchy of taxonomic categories to a basic
category of biological organization
. Moreover, because this important change in the conceptualization of
the species category still has not been fully accepted, it continues to
have important consequences
. For example, as discussed in this paper, its more complete acceptance
provides a simple solution to the species problem, and this solution, in
turn, brings the way in which species are treated in taxonomic practice
into line with claims about the general theoretical significance of the
species category.
References
concept of species.
This contribution had tremendous significance both for systematics in
particular and for biology in general
. It represented a fundamental shift in the conceptualization of the
species category that resulted in a uniquely biological concept of
species and changed the species category from a more-or-less
arbitrary rank in the hierarchy of taxonomic categories to a basic
category of biological organization
. Moreover, because this important change in the conceptualization of
the species category still has not been fully accepted, it continues to
have important consequences
. For example, as discussed in this paper, its more complete acceptance
provides a simple solution to the species problem, and this solution, in
turn, brings the way in which species are treated in taxonomic practice
into line with claims about the general theoretical significance of the
species category.
References
1. ↵
Linnaeus, C. (1753) Species Plantarum (Laurentii Salvii, Stockholm).
Google Scholar
2. ↵
Linnaeus, C. (1758) Systema Naturae, 10th Ed. (Laurentii Salvii,
Stockholm).
Google Scholar
3. ↵
de Queiroz, K. (1997) Aliso 15, 125-144.
Google Scholar
4. ↵
Flexner, S. B. & Hauck, L. C. (1993) Random House Unabridged
Dictionary (Random House, New York).
Google Scholar
5. ↵
Darwin, C. (1859) On the Origin of Species by Means of Natural
Selection (John Murray, London).
Google Scholar
Linnaeus, C. (1753) Species Plantarum (Laurentii Salvii, Stockholm).
Google Scholar
2. ↵
Linnaeus, C. (1758) Systema Naturae, 10th Ed. (Laurentii Salvii,
Stockholm).
Google Scholar
3. ↵
de Queiroz, K. (1997) Aliso 15, 125-144.
Google Scholar
4. ↵
Flexner, S. B. & Hauck, L. C. (1993) Random House Unabridged
Dictionary (Random House, New York).
Google Scholar
5. ↵
Darwin, C. (1859) On the Origin of Species by Means of Natural
Selection (John Murray, London).
Google Scholar
6. ↵
Huxley, J. (1942) Evolution, the Modern Synthesis (Allen and Unwin,
Huxley, J. (1942) Evolution, the Modern Synthesis (Allen and Unwin,
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