Download Darwin and Evolution

Evolution
and
Darwin
Evolution
• The processes that have transformed life on
earth from it’s earliest forms to the vast
diversity that characterizes it today.
• A change in the genes!!!!!!!!
Old Theories of Evolution
• Jean Baptiste Lamarck (early 1800’s) proposed:
“The inheritance of acquired characteristics”
• He proposed that by using or not using its body
parts, an individual tends to develop certain
characteristics, which it passes on to its
offspring.
“The Inheritance of Acquired
Characteristics”
• Example:
A giraffe acquired its long neck because its
ancestor stretched higher and higher into the
trees to reach leaves, and that the animal’s
increasingly lengthened neck was passed on
to its offspring.
Charles Darwin
• Influenced by Charles Lyell who published
“Principles of Geology”.
• This publication led Darwin to realize that
natural forces gradually change Earth’s
surface and that the forces of the past are still
operating in modern times.
Charles Darwin
• Darwin set sail on the H.M.S. Beagle (1831-1836)
to survey the south seas (mainly South America
and the Galapagos Islands) to collect plants and
animals.
• On the Galapagos Islands, Darwin observed
species that lived no where else in the world.
• These observations led Darwin to write a book.
Charles Darwin
• Wrote in 1859:
“On the Origin of Species
by Means of Natural Selection”
• Two main points:
1. Species were not created in their present
form, but evolved from ancestral species.
2. Proposed a mechanism for evolution:
NATURAL SELECTION
Natural Selection
• Individuals with favorable traits are more
likely to leave more offspring better suited for
their environment.
• Also known as “Differential Reproduction”
• Example:
English peppered moth (Biston betularia)
- light and dark phases
Darwin’s 5 points
1. Population has variations.
2. Some variations are favorable.
3. More offspring are produced than
survive
4. Those that survive have favorable
traits.
5. A population will change over time.
• https://www.youtube.com/watch?v=AMt
T5_AQmLg
The making of the fittest
Summary of Natural Selection
• Natural selection is differential success in
reproduction
– That results from the interaction between
individuals that vary in heritable traits and their
environment
• Natural selection can produce an increase over time
– In the adaptation of organisms to their
environment
(a) A flower mantid
in Malaysia
(b) A stick mantid
in Africa
Figure 22.11
Artificial Selection
• The selective breeding of domesticated
plants and animals by man.
• Question:
What’s the ancestor of the domesticated dog?
• Answer: WOLF
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Evidence of Evolution
1. Biogeography:
Geographical distribution of species.
2. Fossil Record:
Fossils and the order in which they appear
in layers of sedimentary rock (strongest
evidence).
Eastern Long Necked Turtle
Evidence of Evolution
3. Taxonomy:
Classification of life forms.
4. Homologous structures:
Structures that are similar because of
common ancestry (comparative anatomy)
Homologous Body
Structures
• Scientists Noticed Animals With
Backbones (Vertebrates) Had
Similar Bone Structure
• May Differ In Form or Function
• Limb Bones Develop In Similar
Patterns
• Arms, Wings, Legs, Flippers
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Homologous Body
Structures
• Structures That Have Different
Mature Forms But Develop From The
Same Embryonic Tissues
• Strong Evidence That All FourLimbed Animals With Backbones
Descended, With Modification, From
A Common Ancestor
• Help Scientist Group Animals
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Homologous Body
Structures
• Not All Serve Important Functions
– Vestigial Organs
• Appendix In Man
• Legs On Skinks
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Homologous Structures
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Evidence of Evolution
5. Comparative embryology:
Study of structures that appear during
embryonic development.
6. Molecular biology:
DNA and proteins (amino acids)
Evidence for Evolution - Comparative Embryology
Similarities In Embryonic Development
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Human Fetus – 5 weeks
copyright cmassengale
24
Chicken
Turtle
Rat
25
Similarities in DNA Sequence
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Population Genetics
• The science of genetic change in
population.
• Remember: Hardy-Weinberg equation.
Population
• A localized group of individuals belonging
to the same species.
Gene Pool
• The total collection of genes in a
population at any one time.
Hardy-Weinberg Principle
• The concept that the shuffling of genes that
occur during sexual reproduction, by itself,
cannot change the overall genetic makeup
of a population.
Hardy-Weinberg Principle
• Remember:
If these conditions are met, the
population is at equilibrium.
• This means “No Change” or “No
Evolution”.
POPULATION GENETICS AND THE HARDYWEINBERG LAW
The Hardy-Weinberg formulas allow
scientists to determine whether evolution
has occurred. Any changes in the gene
frequencies in the population over time can
be detected. The law essentially states
that if no evolution is occurring, then an
equilibrium of allele frequencies will remain
in effect in each succeeding generation of
sexually reproducing individuals. In order
for equilibrium to remain in effect (i.e.
that no evolution is occurring) then the
following five conditions must be met:
• No mutations must occur so that new alleles
do not enter the population.
• No gene flow can occur (i.e. no migration
of individuals into, or out of, the
population).
• Random mating must occur (i.e. individuals
must pair by chance)
• The population must be large so that no
genetic drift (random chance) can cause the
allele frequencies to change.
• No selection can occur so that certain
alleles are not selected for, or against. All
genotypes have equal chance of
reproducing.
Obviously, the Hardy-Weinberg
equilibrium cannot exist in real life.
Some or all of these types of forces
all act on living populations at various
times and evolution at some level
occurs in all living organisms. The
Hardy-Weinberg formulas allow us to
detect some allele frequencies that
change from generation to generation,
thus allowing a simplified method of
determining that evolution is
occurring.
There are two formulas that must be
memorized:
• p2 + 2pq + q2 = 1 and p + q = 1
• p = frequency of the dominant allele in the
population
q = frequency of the recessive allele in the
population
p2 = percentage of homozygous dominant
individuals
q2 = percentage of homozygous recessive
individuals
2pq = percentage of heterozygous
individuals
Macroevolution
• The origin of taxonomic groups higher
than the species level.
Microevolution
• A change in a population’s gene pool
over a secession of generations.
• Evolutionary changes in species over
relatively brief periods of geological time.
Five Mechanisms of Microevolution
1. Genetic drift:
Change in the gene pool of a small
population due to chance.
• Two examples:
a. Bottleneck effect
b. Founder effect
a. Bottleneck Effect
• Genetic drift (reduction of alleles in a population)
resulting from a disaster that drastically reduces
population size.
• Examples:
1. Earthquakes
2. Volcano’s
The Bottleneck Effect
• In the bottleneck effect
– A sudden change in the environment may
drastically reduce the size of a population
– The gene pool may no longer be reflective of
the original population’s gene pool
(a)
Shaking just a few marbles through the
narrow neck of a bottle is analogous to a
drastic reduction in the size of a population
after some environmental disaster. By chance,
blue marbles are over-represented in the new
population and gold marbles are absent.
Figure 23.8 A
Original
population
Bottlenecking
event
Surviving
population
b. Founder Effect
• Genetic drift resulting from the colonization
of a new location by a small number of
individuals.
• Results in random change of the gene pool.
• Example:
1. Islands (first Darwin finch)
Five Mechanisms of Microevolution
2. Gene Flow:
The gain or loss of alleles from a
population by the movement of individuals
or gametes.
• Immigration or emigration.
Five Mechanisms of Microevolution
3. Mutation:
Change in an organism’s DNA that
creates a new allele.
4. Non-random mating:
The selection of mates other than
by chance.
5. Natural selection:
Differential reproduction.
Modes of Action
• Natural selection has three modes of action:
1. Stabilizing selection
2. Directional selection
3. Diversifying selection
Number
of
Individuals
Small
Large
Size of individuals
1. Stabilizing Selection
• Acts upon extremes and favors the
intermediate.
Number
of
Individuals
Small
Large
Size of individuals
2. Directional Selection
• Favors variants of one extreme.
Number
of
Individuals
Small
Large
Size of individuals
3. Diversifying Selection
• Favors variants of opposite extremes.
Number
of
Individuals
Small
Large
Size of individuals
Evidence for Evolution – Evolution Observed
Selection against small guppies results in an increase in
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average size
RESULTS
After 11 years, the average size and age at maturity of guppies in the transplanted
populations increased compared to those of guppies in control populations.
185.6
161.5
85.7 92.3
48.5
58.2
Control Population: Guppies
from pools with pike-cichlids
as predators
67.5 76.1
Males
Females
Males
Females
Experimental Population:
Guppies transplanted to
pools with killifish as
predators
CONCLUSION Reznick and Endler concluded that the change in predator resulted in different variations
in the population (larger size and faster maturation) being favored. Over a relatively short time, this altered
selection pressure resulted in an observable evolutionary change in the experimental population.
• The three modes of selection
Original population
Original
population
Evolved
population
(a) Directional selection shifts the overall
makeup of the population by favoring
variants at one extreme of the
distribution. In this case, darker mice are
favored because they live among dark
rocks and a darker fur color conceals them
from predators.
Fig 23.12 A–C
Phenotypes (fur color)
(b) Disruptive selection favors variants
at both ends of the distribution. These
mice have colonized a patchy habitat
made up of light and dark rocks, with the
result that mice of an intermediate color are
at a disadvantage.
(c) Stabilizing selection removes
extreme variants from the population
and preserves intermediate types. If
the environment consists of rocks of
an intermediate color, both light and
dark mice will be selected against.
Species
• A group of populations whose individuals
have the potential to interbreed and produce
viable offspring.
Speciation
• The evolution of new species.
• Two basic patterns of evolutionary change
can be distinguished
– Anagenesis
– Cladogenesis
Figure 24.2 (a) Anagenesis
(b) Cladogenesis
Reproductive Barriers
• Any mechanism that impedes two species
from producing fertile and/or viable hybrid
offspring.
• Two barriers:
1. Pre-zygotic barriers
2. Post-zygotic barriers
1. Pre-zygotic Barriers
a. Temporal isolation:
Breeding occurs at different times for
different species.
b. Habitat isolation:
Species breed in different habitats.
c. Behavioral isolation:
Little or no sexual attraction between
species.
1. Pre-zygotic Barriers
d. Mechanical isolation:
Structural differences prevent gamete
exchange.
e. Gametic isolation:
Gametes die before uniting with gametes
of other species, or gametes fail to unite.
2. Post-zygotic Barriers
a. Hybrid inviability:
Hybrid zygotes fail to develop or fail to
reach sexual maturity.
b. Hybrid sterility:
Hybrid fails to produce functional gametes.
c. Hybrid breakdown:
Offspring of hybrids are weak or infertile.
Allopatric Speciation
• Induced when the ancestral population
becomes separated by a geographical
barrier.
• Example:
Grand Canyon and ground squirrels
Adaptive Radiation
• Emergence of numerous species from a
common ancestor introduced to new and
diverse environments. Usually happens on
islands (Galapagos and Hawaiian)
• Example:
Darwin’s Finches
• The Hawaiian archipelago
– Is one of the world’s great showcases of
adaptive radiation
1.3 million years
Dubautia laxa
MOLOKA'I
KAUA'I
MAUI
5.1
million
years O'AHU LANAI
3.7
million
years
Argyroxiphium sandwicense
HAWAI'I
0.4
million
years
Dubautia waialealae
Figure 24.12
Dubautia scabra
Dubautia linearis
Sympatric Speciation
• Result of a radical change in the genome that
produces a reproductively isolated subpopulation within the parent population (rare).
• Example: Plant evolution - polyploid
A species doubles it’s chromosome # to
become tetraploid.
Parent population
reproductive
sub-population
Two types of sympatric speciation:
a. autopolyploidy – when the new set of
chromosomes belongs to a single species
b. allopolyploidy – when the new set of
chromosome comes from another species
Polyploidy is much more common in plants
than animals. Ex. Oats, cotton, potatoes,
tobacco and wheat (is allohexaploid)
https://flightline.highline.edu/jbetzzall/BI100/
animations/speciation_models.html
Interpretations of Speciation
• Two theories:
1. Gradualist Model (Neo-Darwinian):
Slow changes in species overtime.
2. Punctuated Equilibrium:
Evolution occurs in spurts of relatively
rapid change.
Time
(a)
Figure 24.13
Gradualism model. Species
descended from a common
ancestor gradually diverge
more and more in their
morphology as they acquire
unique adaptations.
(b)
Punctuated equilibrium
model. A new species
changes most as it buds
from a parent species and
then changes little for the
rest of its existence.
Convergent Evolution
• Species from different evolutionary branches
may come to resemble one another if they live in
very similar environments.
• Example:
1. Ostrich (Africa) and Emu (Australia).
2. Sidewinder (Mojave Desert) and
Horned Viper (Middle East Desert)
• Some similar mammals that have adapted
to similar environments
– Have evolved independently from different ancestors
NORTH
AMERICA
Sugar
glider
AUSTRALIA
Flying
squirrel
Figure 22.17
Coevolution
• Evolutionary change, in which one species
act as a selective force on a second
species, inducing adaptations that in turn act
as selective force on the first species.
• Example:
1. Acacia ants and acacia trees
2. Humming birds and plants with flowers
with long tubes
Polymorphism
• Phenotypic polymorphism
– Describes a population in which two or more
distinct morphs for a character are each
represented in high enough frequencies to be
readily noticeable
• Genetic polymorphisms
– Are the heritable components of characters that
occur along a continuum in a population
Variation Between Populations
• Most species exhibit geographic variation
– Differences between gene pools of separate
populations or population subgroups
Figure 23.10
1
2.4
3.14
5.18
8.11
9.12
10.16
13.17
1
2.19
3.8
4.16
9.10
11.12
13.17
15.18
6
7.15
19
XX
5.14
6.7
XX
• Some examples of geographic variation
occur as a cline, which is a graded change
in a trait along a geographic axis
Heights of yarrow plants grown in common garden
EXPERIMENT
Researchers observed that the average size
Mean height (cm)
of yarrow plants (Achillea) growing on the slopes of the Sierra
Nevada mountains gradually decreases with increasing
elevation. To eliminate the effect of environmental differences
at different elevations, researchers collected seeds
from various altitudes and planted them in a common
garden. They then measured the heights of the
resulting plants.
Atitude (m)
RESULTS The average plant sizes in the common
garden were inversely correlated with the altitudes at
which the seeds were collected, although the height
differences were less than in the plants’ natural
environments.
CONCLUSION The lesser but still measurable clinal variation
in yarrow plants grown at a common elevation demonstrates the
role of genetic as well as environmental differences.
Figure 23.11
Sierra Nevada
Range
Great Basin
Plateau
Seed collection sites
Evolution
of
pesticide
resistance
in
response
to
selection
copyright cmassengale
71
Phylogenies are based on common
ancestries inferred from fossil,
morphological, and molecular
evidence
Lizard
Bird
Mammal
Four-chambered
heart
(a) Mammal-bird clade
Lizard
Bird
Mammal
Four-chambered
heart
Four-chambered
heart
(b) Lizard-bird clade
Lamprey
Tuna
Turtle
Leopard
Salamander
Lancelet
(outgroup)
CHARACTERS
TAXA
Hair
0
0
0
0
0
1
Amniotic (shelled) egg
0
0
0
0
1
1
Four walking legs
0
0
0
1
1
1
Hinged jaws
0
0
1
1
1
1
Vertebral column (backbone)
0
1
1
1
1
1
Turtle
(a) Character table. A 0 indicates that a character is absent; a 1
indicates that a character is present.
Leopard
Hair
Salamander
Amniotic egg
Tuna
Four walking legs
Lamprey
Hinged jaws
Lancelet (outgroup)
Vertebral column
(b) Cladogram. Analyzing the distribution of these
derived characters can provide insight into vertebrate
phylogeny.
Evidence for Evolution – Evolution Observed
Evolution of drug-resistance in HIV
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