Transcript NATURAL SELECTION AT WORK

THEORY OF EVOLUTION
“Evolution explains the diversity & relatedness of life on earth”
GPS – Evolution (Population Genetics and Speciation)
The Idea of Evolution: Descent
with Modification
• Living things share common characteristics
because they are descended from common
ancestors.
• Living things are diverse because each species is
adapted to its own habitat and way of life.
Who was Charles Darwin?
• 1831, became an unpaid
naturalist on board the HMS
Beagle.
• Observed plants and animals
on the Galapagos Islands…
Darwin’s Investigations of the
Galapagos Islands
• Each island had its own species of
giant tortoise in response to the
type of vegetation found on each
island.
• Marine iguanas (only found on the
Galapagos) have similarities to the
land iguanas found in South
America.
• The 13 species of finch on the
islands are similar except for
each having a beak adapted to a
particular way of life.
CHARLES DARWIN DEVELOPS A
THEORY
“On the Origin of Species by Means of Natural Selection”
Darwin’s Observations:
1) Individuals in a population are different
from one another.
2) Organisms produce more offspring than
the environment can support.
3) In spite of the large numbers of offspring,
population size tends to remain the same.
4) Environments are constantly changing.
CHARLES DARWIN DEVELOPS A
THEORY
“On the Origin of Species by Means of Natural Selection”
1) In each population there is a competition for
available resources; only some organisms
survive.
2) Individuals with favorable variations are
more likely to survive and reproduce.
(survival of the fittest)
3) The favorable variation that allows survival
accumulates and eventually appears in the
entire population. (adaptation)
NATURAL SELECTION AT WORK
“Natural Selection Provides a Mechanism for Evolution”
• Natural Selection Check List:
aVariation exists between
individuals.
aOverproduction/struggle
for survival.
aSurvival of the fittest.
(survive and reproduce)
aAdaptation increases in the
population.
The maintenance of variation is beneficial
because populations that lack variation
may not be able to adapt to new conditions
and may become extinct.
What causes Variation?
• Mutations and genetic
recombination.
• Natural Selection reduces,
but does not eliminate, the
range of phenotypes.
A Mutation is a change in the
DNA sequence
Spontaneous mutations affect
the amino acid sequence of a
protein. This new protein may
be beneficial, harmful or have
no affect at all.
New mutations are constantly
being generated in a gene pool.
• A gene pool is all the
genes in a population.
• Mutation is an
important source of
genetic variation within
a gene pool.
How does Natural Selection
determine which genetic traits
are passed on?
• Beetles with brown
genes escaped
predation and survived
to reproduce more
frequently than beetles
with green genes, so
that more brown genes
got into the next
generation.
Over the past 60 years penicillin has
been used to treat bacterial infections.
• Now, however, penicillin has become
ineffective at killing many types of bacteria.
What helped the bacteria become more
resistant?
Organisms Differ in Fitness
What is Fitness?
• The most fit organisms
reproduce and leave more
offspring than the less fit
organisms.
• Natural Selection is the
change caused by the
survival and reproduction
of specific individuals.
Natural selection causes change
within populations
• Organisms best suited to their environment
survive and pass on their traits through their
“genes”.
• The frequency of these “genes” builds up in the
population.
• When this “genetic trait”
builds up in the
entire population it
is called an adaptation.
Natural Selection
determines the
differential survival of
groups of organisms
• An adaptation is a trait
that helps an organism
be more suited to its
environment.
• Natural selection
results in the adaptation
of populations to their
specific environments.
Industrial Melanism
“An Example of Natural Selection”
• The Peppered Moths of Manchester, England
come in two varieties, one darker than the other.
• Before the industrial revolution, the dark moth
was rare; however, during the industrial
revolution the light moth seldom appeared.
• Why?
SPECIATION
“Splitting of one species into two species”
Isolation leads to species formation
• Geographic isolation
physically separates
groups within a
population.
• When populations
become separated,
different environmental
pressures can create
differences between the
two groups.
Allopatric speciation is created
by a geographic barrier
Sympatric speciation is when
populations develop a genetic
difference
• If these differences
become so extreme
that the two
populations can no
longer interbreed they
can, at that point, be
considered two
different “species”.
Reproductive isolation keeps
newly forming
species from interbreeding
Why is species diversity beneficial?
• Increased
diversity among
species increases
the chances that
some species will
adapt to survive
future
environmental
changes.
Fossils Tell The Story …
Fossils - preserved or mineralized
remains or traces of an organism
that lived long ago.
THE FOSSIL RECORD
- Provides evidence for
succession of life over
time (example: the
evolution of the horse).
- Provides transitional
links between groups
of organisms (example:
Archaeopteryx - links
reptiles to birds).
What is a Mass Extinction?
• Periods when a large
percentage of existing
species becomes extinct
within a relatively short
period of time.
Is All life wiped out
during a Mass
Extinction?
• No, but one mass extinction
lost as much as 95% of the
life on earth.
Convergent Evolution
The independent
development of
similar structures in
organisms that are
not directly related
Convergent
evolution is usually
seen in animals and
plants that live in
similar
environments
Analogous structures tend to be
alike but constructed differently
e.g. insect wings and bird wings.
The relationship between insect wings and bird wings is
analogous
The relationship between different bird wings is
homologous
Co-evolution
Two species that
interact with each other
(predator/prey;
mutualistic;
parasite/host;) and act
as selection pressures
on one another
Long legs
Good hearing
Sharp eyesight
Co-evolution
What can cause a Mass Extinction?
• Environmental changes, diseases, loss of
resources, predation, extraterrestrial events
What do Mass Extinction do in
terms of evolution?
- Mass Extinctions allow
evolution to take a new
direction.
- Episodes of speciation are
the most dramatic after a
mass extinction has
cleared the way for new
species take over recently
vacated areas.
Evidence of Evolution
Taxonomy:
Classification of life
forms.
Homologous
structures:
Structures that are
similar because of
common
ancestry
(comparative
anatomy)
Divergent Evolution
• When species with a common ancestor
evolve into very different forms.
• Evidence: homologous structures –
May have the same components but
different a function and or structure.
Evidence cont’d
Comparative
embryology:
Study of
structures that
appear during
embryonic
development.
Molecular biology:
DNA and proteins
(amino acids)
EVIDENCE CONT’D
VESTIGIAL
STRUCTURES:
STRUCTURES
THAT DO NOT
SEEM TO HAVE
A FUNCTION
What adaptation would increase the white turtle’s fitness?
www.msnbc.com
Evolution due to natural selection
• Ex: white turtle will
not survive in nature
(no evolution)
• If sea becomes white,
then white turtle will
have the advantage,
thus green turtles
become extinct
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