Evolution and Biodiversity - PowerPoint PPT Presentation


Title: Evolution and Biodiversity


1
Evolution and Biodiversity
G. Tyler Millers Living in the Environment 14th
Edition Chapter 5
2
Chapter 5 Essential Questions /
Objectives Briefly describe the evolution of life
from chemical evolution to the development of
eukaryotic cells. Briefly describe the theory of
evolution, being sure to include the roles played
by variation within the gene pool and natural
selection, extinction, speciation, and adaptive
radiation. Describe the tools available to
researchers for learning the evolutionary history
of life. (evidence for evolution) Define natural
selection and the three conditions that are
necessary for evolution of a population by
natural selection.
3
Summarize and address two common misconceptions
about evolution. Define coevolution. Distinguish
between a specialist and a generalist. Evaluate
the conditions that favor these two
approaches. Define ecological niche. Distinguish
between condition and resource fundamental niche
and realized niche. List the factors that
determine the realized niche. Define speciation
and compare allopatric speciation with sympatric
speciation. Indicate which of these mechanisms is
more common.
4
Define extinction and distinguish between
background extinction and mass extinction.
Discuss the role of humans on the rate of
extinction at present. Discuss the pros and
cons of artificial selection and genetic
engineering. Consider the possible environmental
impacts on resource use, pollution, and
environmental degradation. Indicate what it is
that has allowed humans to have such a profound
influence
5
Origins and Early Evolution of Life
  • Chemical evolution of organic molecules,
    biopolymers, and systems of chemical reactions
    were needed to form the first cell. It took about
    1 billion years.
  • Biological evolution followed, from single-celled
    prokaryotic bacteria to single-celled eukaryotic
    organisms to multicellular organisms. Is has been
    continuing for 3.7 billion years.
  • Knowledge of past life comes from fossils,
    ice-core drilling, chemical analysis, and DNA
    analysis. These records are incomplete

6
The Theory of Evolution - Widely accepted
scientific idea that all life forms developed
from earlier life forms. Although this theory
conflicts with the creation stories of many
religions, it is the way biologists explain how
life has changed over the past 3.6 - 3.8 billion
years and why it is so diverse today.
The Five Parts of Darwins Theory of
Evolution Perpetual Change Common
Descent Multiplication of Species Gradualism Na
tural Selection
Galapagos Islands satellite view.
7
Darwins Observations and Inferences Observation
1 Organism have great potential
fertility Observation 2 Natural populations
normally remain constant in size except for minor
fluctuations Observation 3 Natural resources
are limited Inference 1 There exists a
continuing struggle for existence among members
of a population Observation 4 All organisms
show variation Observation 5 Some variation is
heritable Inference 2 There is differential
survival and reproduction among varying
organisms in a population
8
What Drives Evolution ?
Variation Meiotic mix Population
Dynamics Mutations
Struggle for Existence Competition Predation Selec
tive advantage
9
  • Natural Selection
  • Process by which a particular beneficial gene
    (or set of genes) is reproduced in succeeding
    generations more than other genes. The result of
    natural selection is a population that contains a
    greater proportion of organisms better adapted to
    certain environmental conditions. Conditions for
    Natural Selection Included
  • There is genetic variation within the population
  • Traits must heritable past from one generation
    to the next
  • The adaptation allows the organism to better
    survive under prevailing environmental
    conditions.
  • Differential reproduction - Phenomenon in which
    individuals with adaptive genetic traits produce
    more living offspring than do individuals without
    such traits.

10
Differential Reproduction
  • Misconceptions about Evolution
  • Evolution is the change in a population's genetic
    makeup over time. Therefore, population evolve
    not individuals
  • Evolution is concerned with leaving the most
    descendants, NOT the strongest ones.
  • There is no master plan to achieve genetic
    perfection.

11
Evolution and Adaptation
Macroevolution long term , large scale
evolutionary changes through which new species
form from ancestral species and other species are
lost through extinction. speciation
Microevolution small genetic changes that occur
in a population. variation within a
species Genes mutate Individuals are
selected Populations evolve
  • Gene pool a collection of genes potentially
    available to members offspring in the next
    generation genetic variability in a population
  • Sexual reproduction leads to random recombination
    of alleles from individual to individual.
  • Coevolution Interacting species can engage in a
    back-and-forth genetic contest in which each
    gains a temporary genetic advantage over the
    other.

Evolutionary Arms Race
12
  • Mutation random changes structure or number of
    DNA molecules in a cell that can be inherited by
    offspring.
  • Mutations occur in two ways
  • Gene DNA is exposed to external agents like X
    rays, chemicals (mutagens), or radioactivity
  • Random mistakes that occur in coded genetic
    instructions
  • Only mutations in reproductive cells are passed
    to offspring.
  • Many mutations are neutral some are deadly and
    a few are beneficial.

Fruit fly (Drosophila melangoaster) Vestigial
Wing.
Fruit fly (Drosophila) adult, dorsal view
13
Types Selection
Stabilizing
Directional demonstrated by the peppered moths
Stabilizing tends to favor the
average Disruptive may lead to speciation
Disruptive
14
What Limits Adaptation?
  • A population's gene pool and its rate of
    reproduction limit the population's ability to
    adapt to new environmental conditions.
  • The only genetic traits that can adapt are those
    already in the gene pool.
  • A population's reproductive capacity limits those
    genes that can adapt.
  • Genetically diverse species that reproduce
    quickly can often adapt quickly.
  • Populations that reproduce slowly take a long
    time to adapt through natural selection.
  • For a new favorable trait to predominate, most of
    an existing population would have to die
    prematurely.

15
The Fossil Record as Evidence for
Evolution Fossils Skeletons, bones, shells, body
parts, leaves, seeds, or impressions of such
items that provide recognizable evidence of
organisms that lived long ago.
Fossil of algae, Gunflint chert, 2.1 billion
years old. Brightfield X400.
Burgess Shale arthropod fossils, 530 years old,
Middle Cambrian Period.
Trilobite fossil from the Silurian period 405mya.
16
Comparative anatomy
Darwin recognized the major source of evidence
for common descent was found in the concept of
homology. Homology is the name given to
similarity of organs or structures due to common
embryonic or evolutionary origin. Forelimbs of
five vertebrates show skeletal homologies
Yellow --- Humerus Blue ---- radius and ulna
Pink ---- wrist White ---- phalanges Clear
homologies of bones and patterns of connection
are evident despite evolutionary modifications
for particular functions
17
Phylogenetic Reconstruction
The phylogenetic pattern specified by 15
homologous structures in the skeletons of ratite
(flightless) birds. The homologous features are
numbered 1-15 and are marked both on the branches
of the tree on which they arose and on the birds
that them
Simplified phylogenetic reconstruction of
vertebrates
18
(No Transcript)
19
Transitional Species
Whale evolution - the movement of the nostrils
from the front of the skull to the top of the
skull Why is having the nostrils at the top of
the skull an advantage?
Environmental changes require adaptations also.
Organisms must be able to adapt to the new
conditions, migrate to an area with a more
favorable environment, or become extinct.
20
DNA Evidence for Evolution
http//www.pbs.org/wgbh/evolution/library/03/4/qui
cktime/l_034_04.html
21
Ice cores unlock climate secrets
Gases and particles trapped in the layers of an
ice core provide information about the Earth's
climate and atmosphere. Oxygen and hydrogen
isotopes reveal the temperature when the ice
formed, for example, while high carbon dioxide
and methane levels indicate periods of global
warming.
22
Geological Time and Major Evolutionary Events
Modern humans (Homo sapiens) appear about 2
seconds before midnight
Photosynthesis and Oxygen Origins of the
Eukaryotic Cells The Cambrian Explosion Movement
on to land
Recorded human history begins 1/4 second before
midnight
Age of mammals
Age of reptiles
midnight
Insects and amphibians invade the land
Origin of life (3.63.8 billion years ago)
First fossil record of animals
Plants begin invading land
noon
Evolution and expansion of life
23
Ecological Niches and Adaptation
  • An ecological niche is a species' way of life in
    an ecosystem, everything that affects its
    survival and reproduction.
  • The niche includes the member's adaptations, its
    range of tolerance for physical and chemical
    conditions, its interactions with other
    components of the ecosystem, and its role in
    energy flow and matter recycling.
  • This is NOT the same as the organism's habitat.
  • The habitat is the physical location where a
    species lives.
  • The fundamental niche is the full potential range
    of conditions and resources a species could use.
  • Its realized niche is the part of the potential
    niche that allows a species to survive and avoid
    competition with other species for the same
    resources

24
Ecological Niches and Adaptation
Fig. 5-4 p. 91
25
Broad and Narrow Niches
  • Generalists
  • Some species have broad ecological roles and are
    termed generalist species.
  • Their living range is broad and includes many
    different places.
  • They can eat a variety of foods and tolerate a
    wide range of environments.
  • If the environment is changeable, the generalist
    will survive better than the specialist.
  • Specialists
  • Some species have narrow ecological roles and are
    termed specialist species.
  • Specialist species can live only in very
    specific environments.
  • This makes them more prone to extinction when
    environmental conditions change.
  • If the environment is constant, specialists have
    fewer competitors.
  • Intense competition may lead to evolutionary
    divergence of a single species into a variety
    ofsimilar species with specialized niches.

26
Speciation A new species arises when members of
a population are isolated from other members so
long that changes in their genetic makeup prevent
them from producing fertile offspring if they get
together again.
Fig. 5-7 p. 94
27
Speciation
  • Natural selection can lead to development of an
    entirely new species.
  • In speciation, two species arise from one when
    some members of a population cannot breed with
    other members to produce fertile offspring.
  • Allopatric Speciation is the most common
    mechanism and occurs in two phases
  • Geographic isolation physical separation for
    long time periods
  • Reproductive isolation the gene pools are so
    changed that members become so different
    ingenetic makeup that they cannot produce
    fertile offspring

28
Allopatric Speciation
  • Exactly how speciation occurs is not well
    understood. Most biologists believe in Allopatric
    (other place) Speciation A small population
    becomes geographically isolated in some way.
  • Breeding only among themselves, its members
    evolve away from the ancestral
  • Humans and chimpanzees diverged, it is believe,
    because the ancestral species was divided by
    Africas Great Rift Valley

29
Sympatric Speciation
  • Sympatric Speciation is less common. It occurs
    when two species live close together but can't
    interbreed due to a mutation or subtle changes in
    behavior.

Sympatric speciation can involve seasonal or
habitat isolation- potential mates arent in the
same place at the same time- or behavioral
isolation, for example when a courtship ritual
develops that appeals to some but not all.
Northern Fence Lizard (Sceloporus undulatus
hyacinthinus) male and female, showing sexual
dimorphism.
30
Extinction
  • When population members cannot adapt to changing
    environmental conditions, the species
    becomesextinct.
  • A species manages to survive one to ten million
    years before extinction occurs.
  • Life has had to cope with many major natural
    disasters that may reduce or eliminate species.
  • Introduction of new species into an area has
    also led to reduction in number or elimination of
    species.
  • When local environmental conditions change, some
    species will disappear at a low rate this is
    called background extinction.
  • Mass extinction is a significant rise in
    extinction rates above the background extinction
    level. Usually, from 25-70 of species are lost.
    Recent evidence suggests that there have been two
    mass extinctions on Earth. There appear to have
    been three mass depletions on Earth.
  • Mass depletions are periods of extinction are
    higher than normal , but not high enough to
    classify as a mass extinction

31
Mass Extinction
Adaptive radiations are recovery periods after
mass extinction when numerous new species evolve
to fill niches in changed environments. It takes
one to ten million years to rebuild biological
diversity after a mass extinction/depletion.

Terrestrialorganisms
1600
Silurian
Triassic
Jurassic
Permian
Devonian
Cambrian
Ordovician
Cretaceous
Marineorganisms
1200
Carboniferous
Pre-cambrain
800
Number of families
Tertiary
Quaternary
400
0
1.8
0
65
145
205
250
290
355
410
440
500
545
3500
Millions of years ago
32
Continental drift plays a role in speciation and
extinction by isolating populations both
geographically and reproductively
120
120
80
80
80
80
40
120
120
135 million years ago
225 million years ago
EURASIA
NORTH AMERICA
AFRICA
120
80
0
120
40
120
120
INDIA
SOUTH AMERICA
65 million years ago
Present
33
Evolutionary tree models
Evolutionary tree diagrams interaction.
Click to view animation.
34
Human Impact on Extinction
  • The Earth's biodiversity is decreasing because of
    human activities.
  • Biodiversity equals speciation minus extinction.
  • Humans are causing the premature extinction of
    species, estimated to be 100 to 1,000 species per
    million species.
  • It has been predicted that by the end of the 21st
    century we may see the extinction of half of the
    present species now on Earth.
  • Humans and their activities are also
    destroying/degrading ecosystems that might be
    centers for future speciation.

35
Human Impacts on Evolution
  • Artificial Selection
  • Genetic Engineering
  • Concerns about Genetic Engineering

36
What is the Future of Evolution?
  • Man has used artificial selection to change the
    genetic characteristics of populations.
  • We use selective breeding to obtain specific
    desired traits.
  • Traditional crossbreeding is a slow process it
    takes many generations of selection for the
    desired trait.

Wild and cultivated roses illustrating artificial
selection.
37
What is the Future of Evolution?
  • Genetic engineering/gene splicing are techniques
    that isolate, modify, multiply, and recombine
    genes from different organisms. Genes from
    different species that would never interbreed in
    nature are being transferred to each other.
  • Genetically modified organisms (GMOs)/transgenic
    organisms are the results of this gene splicing.
  • Gene splicing takes half as much time to develop
    a new crop/animal, as does traditional
    crossbreeding.
  • Cloning produces a genetically identical version
    of an individual.
  • Biopharming is a new field where genetically
    engineered animals act as biofactories to produce
    drugs, vaccines, antibodies, hormones, etc.

38
Phase 2 Make Transgenic Cell
Phase 1 Make Modified Gene
cell
Identify and extract gene with desired trait
Transfer plasmid copies to a carrier agrobacterium
gene
A. tumefaciens (agrobacterium)
DNA
Identify and remove portion of DNA with desired
trait
Agrobacterium inserts foreign DNA into plant cell
to yield transgenic cell
plasmid
Plant cell
Remove plasmid from DNA of E. coli
Nucleus
Host DNA
E. coli
DNA
Foreign DNA
Genetically modified plasmid
Insert extracted DNA (step 2) into plasmid (step3)
Transfer plasmid to surface microscopic
metal particle
plasmid
Insert modified plasmid into E. coli
Use gene gun to inject DNA into plant cell
Grow in tissue culture to make copies
39
Genetic engineering is an unpredictable process
and raises privacy, ethical, legal, and
environmental issues. It is a trial and error
process. The average success rate of genetic
engineering experiments is about 1. There are
many questions about gene therapy Who will be
helped with genetic knowledge only those who
can pay for it? If one has a defect, will he or
she be able to get health insurance, or a job?
Should we clone spare parts for people's bodies?
Phase 3 Grow Genetically Engineered Plant
Transgenic cell from Phase 2
Cell division of transgenic cells
Culture cells to form plantlets
Transfer to soil
Transgenic plants with new traits
40
Genetic Engineering
  • A backlash developed in the 1990s against
    increased use of genetically modified food plants
    and animals.
  • Proponents of more careful control of genetic
    engineering point out that most new technologies
    have had unintended, harmful consequences, so
    caution should be practiced regarding
    geneticengineering.
  • What is the Future of Evolution?
  • Humans have become such a powerful species so
    quickly due to two evolutionary adaptations a
    complex brain and strong opposable thumbs.
  • Humans have quickly developed powerful
    technologies to meet our needs and wants.
  • Humans need to change our ways in order not to be
    called Homo ignoramus instead of Homo sapiens
    sapiens, the doubly wise.

41
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Title: Evolution and Biodiversity


1
Evolution and Biodiversity
G. Tyler Millers Living in the Environment 14th
Edition Chapter 5
2
Chapter 5 Essential Questions /
Objectives Briefly describe the evolution of life
from chemical evolution to the development of
eukaryotic cells. Briefly describe the theory of
evolution, being sure to include the roles played
by variation within the gene pool and natural
selection, extinction, speciation, and adaptive
radiation. Describe the tools available to
researchers for learning the evolutionary history
of life. (evidence for evolution) Define natural
selection and the three conditions that are
necessary for evolution of a population by
natural selection.
3
Summarize and address two common misconceptions
about evolution. Define coevolution. Distinguish
between a specialist and a generalist. Evaluate
the conditions that favor these two
approaches. Define ecological niche. Distinguish
between condition and resource fundamental niche
and realized niche. List the factors that
determine the realized niche. Define speciation
and compare allopatric speciation with sympatric
speciation. Indicate which of these mechanisms is
more common.
4
Define extinction and distinguish between
background extinction and mass extinction.
Discuss the role of humans on the rate of
extinction at present. Discuss the pros and
cons of artificial selection and genetic
engineering. Consider the possible environmental
impacts on resource use, pollution, and
environmental degradation. Indicate what it is
that has allowed humans to have such a profound
influence
5
Origins and Early Evolution of Life
  • Chemical evolution of organic molecules,
    biopolymers, and systems of chemical reactions
    were needed to form the first cell. It took about
    1 billion years.
  • Biological evolution followed, from single-celled
    prokaryotic bacteria to single-celled eukaryotic
    organisms to multicellular organisms. Is has been
    continuing for 3.7 billion years.
  • Knowledge of past life comes from fossils,
    ice-core drilling, chemical analysis, and DNA
    analysis. These records are incomplete

6
The Theory of Evolution - Widely accepted
scientific idea that all life forms developed
from earlier life forms. Although this theory
conflicts with the creation stories of many
religions, it is the way biologists explain how
life has changed over the past 3.6 - 3.8 billion
years and why it is so diverse today.
The Five Parts of Darwins Theory of
Evolution Perpetual Change Common
Descent Multiplication of Species Gradualism Na
tural Selection
Galapagos Islands satellite view.
7
Darwins Observations and Inferences Observation
1 Organism have great potential
fertility Observation 2 Natural populations
normally remain constant in size except for minor
fluctuations Observation 3 Natural resources
are limited Inference 1 There exists a
continuing struggle for existence among members
of a population Observation 4 All organisms
show variation Observation 5 Some variation is
heritable Inference 2 There is differential
survival and reproduction among varying
organisms in a population
8
What Drives Evolution ?
Variation Meiotic mix Population
Dynamics Mutations
Struggle for Existence Competition Predation Selec
tive advantage
9
  • Natural Selection
  • Process by which a particular beneficial gene
    (or set of genes) is reproduced in succeeding
    generations more than other genes. The result of
    natural selection is a population that contains a
    greater proportion of organisms better adapted to
    certain environmental conditions. Conditions for
    Natural Selection Included
  • There is genetic variation within the population
  • Traits must heritable past from one generation
    to the next
  • The adaptation allows the organism to better
    survive under prevailing environmental
    conditions.
  • Differential reproduction - Phenomenon in which
    individuals with adaptive genetic traits produce
    more living offspring than do individuals without
    such traits.

10
Differential Reproduction
  • Misconceptions about Evolution
  • Evolution is the change in a population's genetic
    makeup over time. Therefore, population evolve
    not individuals
  • Evolution is concerned with leaving the most
    descendants, NOT the strongest ones.
  • There is no master plan to achieve genetic
    perfection.

11
Evolution and Adaptation
Macroevolution long term , large scale
evolutionary changes through which new species
form from ancestral species and other species are
lost through extinction. speciation
Microevolution small genetic changes that occur
in a population. variation within a
species Genes mutate Individuals are
selected Populations evolve
  • Gene pool a collection of genes potentially
    available to members offspring in the next
    generation genetic variability in a population
  • Sexual reproduction leads to random recombination
    of alleles from individual to individual.
  • Coevolution Interacting species can engage in a
    back-and-forth genetic contest in which each
    gains a temporary genetic advantage over the
    other.

Evolutionary Arms Race
12
  • Mutation random changes structure or number of
    DNA molecules in a cell that can be inherited by
    offspring.
  • Mutations occur in two ways
  • Gene DNA is exposed to external agents like X
    rays, chemicals (mutagens), or radioactivity
  • Random mistakes that occur in coded genetic
    instructions
  • Only mutations in reproductive cells are passed
    to offspring.
  • Many mutations are neutral some are deadly and
    a few are beneficial.

Fruit fly (Drosophila melangoaster) Vestigial
Wing.
Fruit fly (Drosophila) adult, dorsal view
13
Types Selection
Stabilizing
Directional demonstrated by the peppered moths
Stabilizing tends to favor the
average Disruptive may lead to speciation
Disruptive
14
What Limits Adaptation?
  • A population's gene pool and its rate of
    reproduction limit the population's ability to
    adapt to new environmental conditions.
  • The only genetic traits that can adapt are those
    already in the gene pool.
  • A population's reproductive capacity limits those
    genes that can adapt.
  • Genetically diverse species that reproduce
    quickly can often adapt quickly.
  • Populations that reproduce slowly take a long
    time to adapt through natural selection.
  • For a new favorable trait to predominate, most of
    an existing population would have to die
    prematurely.

15
The Fossil Record as Evidence for
Evolution Fossils Skeletons, bones, shells, body
parts, leaves, seeds, or impressions of such
items that provide recognizable evidence of
organisms that lived long ago.
Fossil of algae, Gunflint chert, 2.1 billion
years old. Brightfield X400.
Burgess Shale arthropod fossils, 530 years old,
Middle Cambrian Period.
Trilobite fossil from the Silurian period 405mya.
16
Comparative anatomy
Darwin recognized the major source of evidence
for common descent was found in the concept of
homology. Homology is the name given to
similarity of organs or structures due to common
embryonic or evolutionary origin. Forelimbs of
five vertebrates show skeletal homologies
Yellow --- Humerus Blue ---- radius and ulna
Pink ---- wrist White ---- phalanges Clear
homologies of bones and patterns of connection
are evident despite evolutionary modifications
for particular functions
17
Phylogenetic Reconstruction
The phylogenetic pattern specified by 15
homologous structures in the skeletons of ratite
(flightless) birds. The homologous features are
numbered 1-15 and are marked both on the branches
of the tree on which they arose and on the birds
that them
Simplified phylogenetic reconstruction of
vertebrates
18
(No Transcript)
19
Transitional Species
Whale evolution - the movement of the nostrils
from the front of the skull to the top of the
skull Why is having the nostrils at the top of
the skull an advantage?
Environmental changes require adaptations also.
Organisms must be able to adapt to the new
conditions, migrate to an area with a more
favorable environment, or become extinct.
20
DNA Evidence for Evolution
http//www.pbs.org/wgbh/evolution/library/03/4/qui
cktime/l_034_04.html
21
Ice cores unlock climate secrets
Gases and particles trapped in the layers of an
ice core provide information about the Earth's
climate and atmosphere. Oxygen and hydrogen
isotopes reveal the temperature when the ice
formed, for example, while high carbon dioxide
and methane levels indicate periods of global
warming.
22
Geological Time and Major Evolutionary Events
Modern humans (Homo sapiens) appear about 2
seconds before midnight
Photosynthesis and Oxygen Origins of the
Eukaryotic Cells The Cambrian Explosion Movement
on to land
Recorded human history begins 1/4 second before
midnight
Age of mammals
Age of reptiles
midnight
Insects and amphibians invade the land
Origin of life (3.63.8 billion years ago)
First fossil record of animals
Plants begin invading land
noon
Evolution and expansion of life
23
Ecological Niches and Adaptation
  • An ecological niche is a species' way of life in
    an ecosystem, everything that affects its
    survival and reproduction.
  • The niche includes the member's adaptations, its
    range of tolerance for physical and chemical
    conditions, its interactions with other
    components of the ecosystem, and its role in
    energy flow and matter recycling.
  • This is NOT the same as the organism's habitat.
  • The habitat is the physical location where a
    species lives.
  • The fundamental niche is the full potential range
    of conditions and resources a species could use.
  • Its realized niche is the part of the potential
    niche that allows a species to survive and avoid
    competition with other species for the same
    resources

24
Ecological Niches and Adaptation
Fig. 5-4 p. 91
25
Broad and Narrow Niches
  • Generalists
  • Some species have broad ecological roles and are
    termed generalist species.
  • Their living range is broad and includes many
    different places.
  • They can eat a variety of foods and tolerate a
    wide range of environments.
  • If the environment is changeable, the generalist
    will survive better than the specialist.
  • Specialists
  • Some species have narrow ecological roles and are
    termed specialist species.
  • Specialist species can live only in very
    specific environments.
  • This makes them more prone to extinction when
    environmental conditions change.
  • If the environment is constant, specialists have
    fewer competitors.
  • Intense competition may lead to evolutionary
    divergence of a single species into a variety
    ofsimilar species with specialized niches.

26
Speciation A new species arises when members of
a population are isolated from other members so
long that changes in their genetic makeup prevent
them from producing fertile offspring if they get
together again.
Fig. 5-7 p. 94
27
Speciation
  • Natural selection can lead to development of an
    entirely new species.
  • In speciation, two species arise from one when
    some members of a population cannot breed with
    other members to produce fertile offspring.
  • Allopatric Speciation is the most common
    mechanism and occurs in two phases
  • Geographic isolation physical separation for
    long time periods
  • Reproductive isolation the gene pools are so
    changed that members become so different
    ingenetic makeup that they cannot produce
    fertile offspring

28
Allopatric Speciation
  • Exactly how speciation occurs is not well
    understood. Most biologists believe in Allopatric
    (other place) Speciation A small population
    becomes geographically isolated in some way.
  • Breeding only among themselves, its members
    evolve away from the ancestral
  • Humans and chimpanzees diverged, it is believe,
    because the ancestral species was divided by
    Africas Great Rift Valley

29
Sympatric Speciation
  • Sympatric Speciation is less common. It occurs
    when two species live close together but can't
    interbreed due to a mutation or subtle changes in
    behavior.

Sympatric speciation can involve seasonal or
habitat isolation- potential mates arent in the
same place at the same time- or behavioral
isolation, for example when a courtship ritual
develops that appeals to some but not all.
Northern Fence Lizard (Sceloporus undulatus
hyacinthinus) male and female, showing sexual
dimorphism.
30
Extinction
  • When population members cannot adapt to changing
    environmental conditions, the species
    becomesextinct.
  • A species manages to survive one to ten million
    years before extinction occurs.
  • Life has had to cope with many major natural
    disasters that may reduce or eliminate species.
  • Introduction of new species into an area has
    also led to reduction in number or elimination of
    species.
  • When local environmental conditions change, some
    species will disappear at a low rate this is
    called background extinction.
  • Mass extinction is a significant rise in
    extinction rates above the background extinction
    level. Usually, from 25-70 of species are lost.
    Recent evidence suggests that there have been two
    mass extinctions on Earth. There appear to have
    been three mass depletions on Earth.
  • Mass depletions are periods of extinction are
    higher than normal , but not high enough to
    classify as a mass extinction

31
Mass Extinction
Adaptive radiations are recovery periods after
mass extinction when numerous new species evolve
to fill niches in changed environments. It takes
one to ten million years to rebuild biological
diversity after a mass extinction/depletion.

Terrestrialorganisms
1600
Silurian
Triassic
Jurassic
Permian
Devonian
Cambrian
Ordovician
Cretaceous
Marineorganisms
1200
Carboniferous
Pre-cambrain
800
Number of families
Tertiary
Quaternary
400
0
1.8
0
65
145
205
250
290
355
410
440
500
545
3500
Millions of years ago
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Continental drift plays a role in speciation and
extinction by isolating populations both
geographically and reproductively
120
120
80
80
80
80
40
120
120
135 million years ago
225 million years ago
EURASIA
NORTH AMERICA
AFRICA
120
80
0
120
40
120
120
INDIA
SOUTH AMERICA
65 million years ago
Present
33
Evolutionary tree models
Evolutionary tree diagrams interaction.
Click to view animation.
34
Human Impact on Extinction
  • The Earth's biodiversity is decreasing because of
    human activities.
  • Biodiversity equals speciation minus extinction.
  • Humans are causing the premature extinction of
    species, estimated to be 100 to 1,000 species per
    million species.
  • It has been predicted that by the end of the 21st
    century we may see the extinction of half of the
    present species now on Earth.
  • Humans and their activities are also
    destroying/degrading ecosystems that might be
    centers for future speciation.

35
Human Impacts on Evolution
  • Artificial Selection
  • Genetic Engineering
  • Concerns about Genetic Engineering

36
What is the Future of Evolution?
  • Man has used artificial selection to change the
    genetic characteristics of populations.
  • We use selective breeding to obtain specific
    desired traits.
  • Traditional crossbreeding is a slow process it
    takes many generations of selection for the
    desired trait.

Wild and cultivated roses illustrating artificial
selection.
37
What is the Future of Evolution?
  • Genetic engineering/gene splicing are techniques
    that isolate, modify, multiply, and recombine
    genes from different organisms. Genes from
    different species that would never interbreed in
    nature are being transferred to each other.
  • Genetically modified organisms (GMOs)/transgenic
    organisms are the results of this gene splicing.
  • Gene splicing takes half as much time to develop
    a new crop/animal, as does traditional
    crossbreeding.
  • Cloning produces a genetically identical version
    of an individual.
  • Biopharming is a new field where genetically
    engineered animals act as biofactories to produce
    drugs, vaccines, antibodies, hormones, etc.

38
Phase 2 Make Transgenic Cell
Phase 1 Make Modified Gene
cell
Identify and extract gene with desired trait
Transfer plasmid copies to a carrier agrobacterium
gene
A. tumefaciens (agrobacterium)
DNA
Identify and remove portion of DNA with desired
trait
Agrobacterium inserts foreign DNA into plant cell
to yield transgenic cell
plasmid
Plant cell
Remove plasmid from DNA of E. coli
Nucleus
Host DNA
E. coli
DNA
Foreign DNA
Genetically modified plasmid
Insert extracted DNA (step 2) into plasmid (step3)
Transfer plasmid to surface microscopic
metal particle
plasmid
Insert modified plasmid into E. coli
Use gene gun to inject DNA into plant cell
Grow in tissue culture to make copies
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Genetic engineering is an unpredictable process
and raises privacy, ethical, legal, and
environmental issues. It is a trial and error
process. The average success rate of genetic
engineering experiments is about 1. There are
many questions about gene therapy Who will be
helped with genetic knowledge only those who
can pay for it? If one has a defect, will he or
she be able to get health insurance, or a job?
Should we clone spare parts for people's bodies?
Phase 3 Grow Genetically Engineered Plant
Transgenic cell from Phase 2
Cell division of transgenic cells
Culture cells to form plantlets
Transfer to soil
Transgenic plants with new traits
40
Genetic Engineering
  • A backlash developed in the 1990s against
    increased use of genetically modified food plants
    and animals.
  • Proponents of more careful control of genetic
    engineering point out that most new technologies
    have had unintended, harmful consequences, so
    caution should be practiced regarding
    geneticengineering.
  • What is the Future of Evolution?
  • Humans have become such a powerful species so
    quickly due to two evolutionary adaptations a
    complex brain and strong opposable thumbs.
  • Humans have quickly developed powerful
    technologies to meet our needs and wants.
  • Humans need to change our ways in order not to be
    called Homo ignoramus instead of Homo sapiens
    sapiens, the doubly wise.

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Resources http//www.pbs.org/wgbh/evolution/
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