How do new species arise?
-- Speciation -• Species: group of organisms that can
interbreed and produce fertile offspring
• Speciation: the process by which genetically
distinct species arise.
Speciation: Formation of new species
• As adaptations and differences accumulate,
the organisms become so different that they
cannot interbreed (reproduce) anymore
• The Unit of Evolution is a Population:
A population is a group
of individuals, of the
same species, living in
the same area, that
interbreed (reproduce)
• Populations Have Genetic
Variation (Variability)
Individuals in a population are
different. Small differences are
determined by their genes
(DNA sequences)
Speciation:
Formation of New Species
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If a population becomes separated, or a group of
individuals becomes isolated, they may change over
time.
They may change so much that they cannot
interbreed anymore with the members of the
original population. Reproductive Isolation.
Reproductive Isolation is the first step towards the
formation of a new species
What influences reproductive isolation:
1. Geographic Isolation
2. Behavioral Isolation
3. Temporal Isolation
1. Geographic Isolation
• A physical barrier separates (splits) the original
population
• As time passes, the environment may selects
for different traits and the 2 populations become
genetically different AND can’t reproduce
• Barriers: Rivers, mountains, bodies of water
Kaibab and Abert Squirrels
Kaibab
Abert
- The Kaibab squirrel
(Sciurus aberti
kaibabensis) became
geographically
isolated from the
common ancestor
about 10,000 years
ago.
- Its closest relative is
the Abert squirrel
(Sciurus aberti aberti)
- They live in opposite
sides of the Grand
Canyon
Example: Emus, ostriches, rheas, Cassowaries,
• Common ancestor lived in the continent of
Gondwana (all southern continents together)
• When Gondwana broke up, the populations
separated and changed over time. All these
birds are closely related but live far apart.
Wrasses: Original population split up when the
isthmus of Panama was formed
- 2 species now, one on each side of Central America
2. Temporal Isolation
(Time of Reproduction)
• Groups of individuals reproduce at different
times. The genes of the 2 groups do not mix.
• It is happening now with some of the migratory
birds that decide not to migrate.
• The birds that do not migrate start mating
before the migratory ones come back.
• Eventually they might become different enough
that they may not recognize each other.
Robins usually migrate south to warmer climates.
Some are not migrating. They reproduce before
the migrating individuals return.
Reproductive Isolation
3. Behavioral Isolation
(Reproductive Behavior changes)
• If 2 populations have different
courtship behaviors, they will not
be able to interbreed
• Different songs (birds) or mating
calls (frogs)
• Different scents (smells)
• A simple mutation can cause a change
How fast is evolution?
How fast do organisms change?
Gradualism
Punctuated Equilibrium
Gradualism
• Organisms go through gradual and
continuous change
Punctuated Equilibrium
• Organisms go through fast periods of change,
followed by long periods of no change
(according to fossil record)
Punctuated Equilibrium
Proposed by Stephen Jay Gould
(1941-2002)
Gradualism
Punctuated Equilibrium
Patterns of Evolution:
1. Convergent Evolution
• Convergent Evolution: When 2 or more
unrelated species become more similar due to
similar adaptations to their environment.
Patterns of Evolution:
2. Divergent Evolution-Adaptive Radiation
• Divergent
Evolution: when
related species
become more
different as they
adapt to different
environments
• Divergent evolution
leads to Adaptive
Radiation
• As species change over evolutionary time, the
DNA sequences in their genes acquired slight
changes.
• According to evolutionary theory, these changes in
DNA and thus proteins accumulate over time.
• Species that diverged from each other long ago
have more differences in their DNA, than species
that diverged recently.
• Scientists use this degree of difference as a
molecular clock to help them predict how long
ago species split apart from one another.
• More Differences = less related, more time since
split from common ancestor.
• Fewer Differences = more related, less time since
split from common ancestor.