Species shape and other structural features. (Jane B.

Species and speciation

Introduction

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Species
is a taxonomic concept used in Biology to refer to a population of organisms
that are in some important ways similar. The idea of species has a long
history. After thousands of years of use, the concept remains central to
biology and a host of related fields, and yet also remains at times ill-defined
and controversial. In this article, the formation and evolution of new species
will be discussed.

 

Species concepts

 

There
are mainly five concepts of species.

 

Biological concept of species

Biological
concept of species is the most commonly used concept. It defines a species as a
group of populations whose members have the potential to interbreed in nature
and produce viable, fertile offspring but do not produce viable, fertile
offspring with members of other such groups. (Jane B. Reece, 2015) Members of a
biological species are defined in terms of reproductive compatibility. Gene
flow is the transfer of alleles between populations. Gene flow occurs between
the different populations of a species and the ongoing exchange of alleles tends
to hold the populations together genetically. Individuals who mate and produce
fertile offspring are considered belong to same species. For example, although
horse and donkey can mate and produce mules, mules are non-fertile offspring,
so horse and donkeys are still different species.

 

Ecological concept of species

The
Ecological Species Concept defines a species in terms of its ecological niche,
i.e. the sum of how members of the species interact with the non-living and
living parts of their environment. (Jane B. Reece, 2015) For example, two
species of Galapagos finches may be similar in appearance but distinguishable
based on what they feed on, so they are consider being different species. This
is less commonly used because niches are generally difficult to identify as it involves
the interaction between the organism and its environment.

 

Morphological concept of species

The
Morphological Species Concept defines a species in terms of its body shape and
other structural features. (Jane B. Reece, 2015) This was wildly used
in past day because at that time, molecular biology was no so developed and
people can only distinguish different species by observing their appearances.
However, this is less useful than the biological concept of species because
sometimes the same living environment give different species similar
appearances, so they may be mistakenly regarded as same species while there is
no gene flow among them. Morphological concept of species is still wildly used
in daily life but it is less convinced than biological concept.

Phylogenetic concept of species

The
Phylogenetic Species Concept defines a species as the smallest group of
individuals who share a common ancestor, forming one branch on the tree of
life. (Jane B. Reece, 2015)

Genetic concept of species

The
Genetic Concept of Species defines a genetic species as a group of genetically
compatible interbreeding natural populations that is genetically isolated from
other such groups. (Jane B. Reece, 2015) Genetic concept
focuses more on genetic isolation rather than what being discusses under
biological concept, reproductive isolation.

 

Formation and
evolution of new species

 

Uniformitariansm and Darwin’s idea

 

Uniformitariansm
was popularized by geologist Charles Lyell’s Priciples of Geology in 1830. He claimed that the earth’s history
was a slow, gradual process punctuated by occasional natural catastrophic events.
(Wikipedia, 2018) Uniformitariansm has
the assumption that natural laws are the same in different fields. Darwin was
heavily influenced by Lyell’s idea and became a supporter of uniformitariansm. In
the aspect of evolution, he believed that the evolution process was also a slow
but continuous process.

 

In
1859, Darwin published On the Origin of
Species and stated his hypothesis of evolution in the book. This ushered in
a scientific revolution—the era of evolutionary biology. He mainly addressed
two ideas in the book, descent with modification and natural selection. Descent
with modification means that many species on earth today are descendants of
ancestral species (Jane B. Reece, May 20, 2015) .During the process,
genetic changes occurred and led to the differences among species. Over time,
populations were evolved to different species but they are related because they
have a common ancestor. On the other hand, natural selection is the mechanism
of those evolutionary changes. In other words, new species are formed base on ancestral
organisms, the force that driven them to evolve is natural selection.

 

There
are many evidence supporting Darwin’s idea, one of them is the fossil record.
Although current found fossils do show the trend of continuous evolution of
species, there are still missing links in between. Darwin believed the missing
stages were present but just not found by us. However, some scientists proposed
opposite opinions.

 

Catastrophism to punctuated equilibrium

Catastrophism
was popularized by George Cuvier, a French naturalist. He was strongly against
to Darwin’s evolution theory. He believed that the species that appeared as
fossil will not evolve any more, until the species became extinct, its anatomy
will remain unchanged. That was the former idea of punctuated equilibrium.

 

In
1972, Niles Eldredge and Stephen Jay Gould proposed the ide of punctuated equilibrium.
It stated that the evolution and formation of species was a sudden event but
not continuously evolved from the ancestral species. At certain occasion,
evolution suddenly occurs at a rapid rate, new species burst out. After that,
the species will enter a relatively constant phase where no evolution process
takes place, this is called the equilibrium. The punctuated equilibrium theory
provided an alternative explanation on the missing links in fossil records.
Punctuated equilibrium is not a theory that against Darwin’s evolution theory
but an add-on to it.

 

Modern evolutionary ideas and synthesis

Modern
synthesis compiles Darwin’s theory with Mendel’s genetics, redefined the theory
of evolution. The concepts in the modern synthesis theory are natural selection,
genetic variations and isolation mechanisms that lead to speciation. (BYJU’s
biology, February 23, 2017)

The
natural selection factory in modern synthesis theory is similar to Darwin’s
theory, both of them agree that natural selection is the force that driven
evolution. Modern synthesis added on genetic variations concept to evolution.
Base on Mendel’s theory and its extension, the recombination of new genotypes
many form new species. During meiosis, the crossing over process also allows
gene recombination. Furthermore, mutations also caused variations in offspring
that may lead to the formation of new species.

 

There
are three main isolating mechanisms which give rise to speciation, namely, geographical
isolation, physiological isolation and behavioural isolation.

 

Geographical
isolation gives rise to allopatric speciation. In allopatric speciation, gene
flow is interrupted when a population is divided into geographically isolated
subpopulations. Once geographic separation has occurred, the separated gene
pools may diverge. Different mutations arise, and natural selection and genetic
drift may alter allele frequencies in different ways in the separated
populations. Reproductive isolation may then arise as a by-product of selection
or drift having caused the populations to diverge genetically.

 

Physiological
and behavioural isolation gives rise to sympatric speciation. In sympatric speciation,
speciation occurs from a population that lives in the same geographic area and
gene flow is interrupted by reproductive barriers. In physiological isolation, mating
is attempted but morphological differences prevent its successful completion.
In behavioural isolation, courtship rituals that attract mates and other
behaviours unique to a species are effective reproductive barriers, even
between closely related species. Such behavioural rituals enable mate
recognition – a way to identify potential mates of the same species.

 

 

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