Speciation is the evolutionary process where populations evolve to become distinct species, primarily described by Charles Darwin, who highlighted natural and sexual selection as mechanisms. There are four geographic modes of speciation: allopatric, peripatric, parapatric, and sympatric, each defined by the level of isolation between populations. The process typically involves three stages: isolation of populations, divergence of traits, and reproductive isolation.

1. Dr. P.B.Reddy
M.Sc,M.Phil,Ph.D, FIMRF,FICER,FSLSc,FISZS,FISQEM
PG DEPARTMENT OF ZOOLOGY
GOVERTNAMENT PG COLLEGE, RATLAM.M.P
reddysirr@gmail.com
Mechanism of speciation

3. Multiply, vary, let the strongest live and the weakest die.”
― Charles Darwin

4. Speciation is the evolutionary process by which populations evolve to become
distinct species.
The biologist Orator F. Cook coined the term in 1906 for cladogenesis, the splitting
of lineages, as opposed to anagenesis, phyletic evolution within lineages.
Charles Darwin was the first to describe the role of natural selection in speciation
in his 1859 book On the Origin of Species. He also identified sexual selection as a
likely mechanism, but found it problematic.

5.  The process by which a new species develops from the
existing species is known as speciation.
Charles Darwin was the first to describe the role of natural
selection in speciation in his 1859 book On the Origin of
Species. He also identified sexual selection as a likely
mechanism, but found it problematic.
A species can be defined as one or more populations of
interbreeding organisms that are reproductively isolated in
nature from all other organisms.
 When populations no longer interbreed, they are thought to
be separate species.
 There are four geographic modes of speciation in nature,
based on the extent to which speciating populations are
isolated from one another: allopatric, peripatric, Parapatric,
and sympatric.
Speciation may also be induced artificially, through animal
husbandry, agriculture, or laboratory experiments.

6. 3 steps of speciation
Speciation has been observed as a three-stage process:
1. Isolation of populations.
2. Divergence in traits of separated populations (e.g. mating system or
habitat use).
3. Reproductive isolation of populations that maintains isolation when
populations come into contact again (secondary contact).
Types of isolating mechanisms
Ecological Isolation. ...
Temporal Isolation. ...
Behavioral Isolation. ...
Mechanical or Chemical Isolation. ...
Geographical Isolation.
Basic mechanisms of evolution
Describe the four basic causes of evolution: natural selection, mutation,
genetic drift, and gene flow.

7.  Allopatric speciation: It is regarded as the most common type of speciation. It involves the
physical separation of a species into two groups. This may occur due to climatic changes,
movement of tectonic plates leading to the fragmentation of a mass of land, or eruption of a
land mass, formation of waterways, or due to the presence of an impassable mountain range.
 Parapatric mode of speciation: It occurs due to partial spatial isolation of populations, and is
characterized by a small overlap in their ranges as well as significant gene flow amongst the
populations. However, the gene flow reduces due to changes in the local conditions, and the
two populations become reproductively isolated.
 Sympatric mode of speciation: It involves the formation of new species due to a genetic
divergence among a few members of the species inhabiting a single geographic area. Unlike the
other modes of speciation, here genetic divergence does not arise due to increase in geographic
distance, but occurs within the same niche.
 Peripatric speciation was Proposed by Ernst Mayr. In this type of speciation, a small group of
members inhabiting a peripheral region of the range undergo reproductive isolation to form a
new species. Many a time, it is considered to be a variation of allopatric speciation.

8. Modes of Speciation
Allopatric Speciation VS Sympatric Speciation

10. Pre-zygotic
barriers are
obstacles that
are present
before an egg
can be
fertilized.
Post-zygotic barriers mean
the animals mated but no
offspring occurred after
they did so. It can also
mean the offspring is a
hybrid and is not viable,
sterile or both.