Transcript evolution by natural selection

EVOLUTION AND NATURAL SELECTION
Darwin’s dangerous idea: evolution by natural
selection
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Lectures by Mark Manteuffel, St. Louis Community College ; Clicker Questions by Kristen Curran, University of Wisconsin-Whitewater
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EVOLUTION IN ACTION
We can see evolution occur right before us.
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COULD YOU BREED
FRUIT FLIES WHO
COULD LIVE LONGER
THAN 20 HOURS ON
AVERAGE?
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When these eggs hatch, do you think the flies in this new
generation will live longer than 20 hours without food?
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A POPULATION OF FRUIT FLIES WAS STARVED
UNTIL 80% OF THE FLIES WERE DEAD. THE
REMAINING FLIES WERE FED AND OFFSPRING WERE
PRODUCED.
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AFTER 60 GENERATIONS THE AVERAGE STARVATION
RESISTANCE OF FRUIT FLIES WAS 160 HOURS
1.
They are genetically identical to the
original population.
2.
They are genetically different from the
original population.
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WHAT HAPPENED?
o
Evolution
o
Natural selection
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EXPERIMENTS IN EVOLUTION
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o
Dogs?
o
Rabbits?
EVOLUTION
o
How does evolution occur?
o
What types of changes can evolution cause in a
population?
o
Five primary lines of evidence
o
Evolution by natural selection
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It is indeed remarkable that this theory
[evolution] has been progressively accepted by
researchers, following a series of discoveries in
various fields of knowledge.
The convergence, neither sought nor
fabricated, of the results of work that was
conducted independently is in itself a significant
argument in favor of this theory.
—Pope John Paul II, 1996
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NATURAL CHANGES
o
The characteristics of individuals in a population
can change over time.
o
We can observe such change in nature and can
even cause such change to occur.
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DARWIN’S JOURNEY TO AN IDEA
A job on a ’round-the-world survey ship allowed Darwin to
indulge and advance his love of nature.
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A JOB ON A ‘ROUND-THE-WORLD SURVEY SHIP
ALLOWED DARWIN TO INDULGE AND ADVANCE
HIS LOVE OF NATURE.
o
Age 16, University of Edinburgh, medical
studies
o
Studied theology at Cambridge University
o
His real love: study of nature
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DARWIN’S JOURNEY TO AN IDEA
Before Darwin, most people believed that all species had
been created separately and were unchanging.
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Georges Buffon was the first to study what is
now known as biogeography.
• places on different continents had similar
environments,
• they had similar, but unique, wildlife that
lived in them.
• Over time, the different species would
adapt
• The world must be older if there was time
to adapt
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JEAN-BAPTISTE LAMARCK
o
Biologist, early 1800s
o
o
Living species might change over time.
If we need to jump higher we will learn to jump higher
and pass this quality on to our children
o
If we don’t need gills, we will not grow gills any more.
o
Use it or lose it.
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CHARLES LYELL & JAMES HUTTON
o
Geologist
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1830 book Principles of Geology
o
o
o
Geological forces had shaped the earth and were continuing
to do so.
Gradual but constant change
Darwin had this book with him on the Beagle
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EMERGING BELIEFS
o
People used to think that the earth was 6,000 years old
and that species were unchanging.
o
In the 18th and 19th centuries, scientists began to
change their beliefs.
o
These changes helped shape Darwin’s thinking.
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DARWIN’S 5-YEAR JOURNEY
http://www.nhm.ac.uk/nature-online/science-ofnatural-history/expeditions-collecting/beaglevoyage/
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DIFFERENT INFLUENCES ON
DARWIN’S IDEAS
Observing geographic similarities and differences among
fossils and living plants and animals, Darwin developed a
theory of evolution.
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TWO IMPORTANT AND UNEXPECTED PATTERNS:
1. THINGS THAT LOOK ALIKE ARE NOT THE SAME
SPECIES.
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1. THINGS THAT LOOK ALIKE ARE NOT THE
SAME SPECIES.

13 Different Finch Species
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2. THE FOSSILS OF EXTINCT SPECIES AND THE
LIVING SPECIES IN THAT SAME AREA RESEMBLE
EACH OTHER.
o
Glyptodonts and armadillos
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2. THE FOSSILS OF EXTINCT SPECIES AND THE
LIVING SPECIES IN THAT SAME AREA RESEMBLE
EACH OTHER.

If no giants exist today, then living things must
change.
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DARWIN’S FOSSILS
The slides were made by slicing and polishing the fossils into
translucent sheets and then placing them between two glass plates
so they could be studied under a microscope.
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DARWIN’S FOSSILS
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DARWIN’S FOSSILS
These images were made available by the Royal
Holloway, University of London on Jan. 17,
2012 . and were collected by Charles Darwin
during the course of his famous "Voyage of the
Beagle." (University of London, Kevin D'Souza
Ho,AP Photo/Royal Holloway)
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THOMAS MALTHUS
o
Economist
o
Essay on the Principle of Population
- populations can grow much faster than the food
supply. We will eat ourselves out of existence in
the foreseeable future.
o
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THE BOOK THAT WOULD “ROCK THE WORLD”
o
1842 first draft
o
14 years in a drawer
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DARWIN’S JOURNEY TO AN IDEA
In 1858, Darwin published his thoughts on natural
selection after decades of percolating and
procrastinating
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HISTORICAL PROGRESS
o
After putting off publishing his thoughts on
natural selection for more than 15 years, Darwin
did so only after Alfred Russel Wallace
independently came up with the same idea.
o
They published a joint presentation on their
ideas in 1858 and Darwin published a much
more detailed treatment in The Origin of Species
in 1859, sparking wide debate and discussion of
natural selection.
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THE OBSERVATIONS DARWIN MADE DURING HIS
TRIP ON THE HMS BEAGLE?
1.
2.
3.
The earth is shaped by gradual forces. (Lyell)
The earth is older than 6,000 years. (Buffon)
Populations could grow beyond the ability of the
environment to support them. (Malthus)
Malthus thesis was that the population of England
would soon reach a point that was impossible to feed
with the island’s resources.
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FOUR MECHANISMS CAN GIVE RISE TO
EVOLUTION.
Allele frequencies in a population
change.
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ALLELE FREQUENCIES
Increase the white phenotype through
breeding.
o
As the generations go by
o
- Higher proportion of white tigers
o
Evolution = change in allele frequencies of the
population
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INDIVIDUALS DO NOT EVOLVE.
o
Populations evolve – get better with the resources they
have
o
Allele frequencies – dark colored moths on dark tree
trunks
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4 MECHANISMS OF EVOLUTIONARY
CHANGE
1.
Mutation
2.
Genetic drift
3.
Migration
4.
Natural selection
Evolution is genetic change in a population.
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FOUR MECHANISMS OF EVOLUTIONARY
CHANGE
Mutation
1.
—a direct change in
the DNA of an individual—the ultimate
source of all genetic variation.
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MUTATION
o
An alteration of the base-pair sequence of an
individual’s DNA
o
When this alteration occurs in a gene, the change in
the DNA sequence may change the allele.
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MUTATION IS THE
ULTIMATE SOURCE
OF GENETIC
VARIATION IN A
POPULATION.
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WHAT CAUSES MUTATIONS?
o
The process of cells dividing can go awry.
o
Environmental phenomena
o
o
mutagens
Mutations are random
o
o
Beneficial?
Detrimental?
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TANNING BEDS BOMBARD THE BODY
WITH ULTRAVIOLET RADIATION.
Can they cause mutations?
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MOBILE PHONES RELEASE RADIATION.
Can they cause brain tumors?
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MUTATION
o
An alteration of the base-pair sequence in an
individual’s DNA.
o
It is Evolution if it changes an allele the individual
carries.
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NEARLY ALL MUTATIONS REDUCE AN
ORGANISM’S FITNESS.
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FOUR MECHANISMS CAN GIVE RISE TO
EVOLUTION.
Genetic drift
2.
is a random
change in allele frequencies in a
population.
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GENETIC DRIFT IS NOT NATURAL
SELECTION:
The change in allele frequencies does not influence
reproductive success.
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THE IMPACT OF GENETIC DRIFT IS
MUCH GREATER IN SMALL
POPULATIONS THAN IN LARGE
POPULATIONS.
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FIXATION
o
Genetic drift can lead to fixation for one allele for a
gene in a population.
o
If this happens, there is no more variability in the
population for this gene.
o
Genetic drift reduces the genetic variation in a
population.
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GENETIC DRIFT IN POPULATIONS
THE FOUNDER EFFECT
POPULATION BOTTLENECKS
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FOUNDER EFFECT
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AMISH PEOPLE ARE MORE LIKELY TO HAVE
EXTRA FINGERS AND TOES
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POPULATION BOTTLENECKS
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GENETIC DRIFT
o
A random change in allele frequencies within a
population,
o
A significant agent of evolutionary change primarily in
small populations.
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FOUR MECHANISMS CAN GIVE RISE TO
EVOLUTION.
Migration
3.
into or out of a
population may change allele
frequencies.
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Migration, also called gene flow,
is the movement of some
individuals of a species from one
population to another.
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MIGRATION
o
Migration, or gene flow, leads to a change in allele
frequencies in a population as individuals move into or
out of the population.
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FOUR MECHANISMS CAN GIVE RISE TO
EVOLUTION.
Natural Selection
4.
–random
changes in a population produce an
individual better suited to its
environment
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NATURAL SELECTION
1.
There must be variation for the particular
trait within a population.
2.
That variation must be inheritable.
3.
Individuals with one version of the trait
must produce more offspring than those with
a different version of the trait.
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CONDITION 1: VARIATION FOR A
TRAIT
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CONDITION 2: HERITABILITY
We call the transmission of traits from parents to
their children through genetic information
inheritance or heritability.
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CONDITION 3: DIFFERENTIAL
REPRODUCTIVE SUCCESS
1.
There are more organisms born than can
survive.
2.
Organisms are continually struggling for
existence.
3.
Some organisms are more likely to win this
struggle and survive and reproduce.
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DIFFERENTIAL REPRODUCTIVE SUCCESS
- The runt of the litter,
less chance of survival.
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MOST AGRICULTURAL PESTS EVOLVE
RESISTANCE TO PESTICIDES.
How does this happen?
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RABBITS HAVE EVOLVED DUE TO
INTERACTIONS WITH PREDATORS
1.
2.
Speed
Coat color
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THROUGH NATURAL SELECTION, POPULATIONS
OF ORGANISMS CAN BECOME ADAPTED TO
THEIR ENVIRONMENT.
Traits causing individuals to have more
offspring than others become more
prevalent.
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“SURVIVAL OF THE FITTEST”
o
Reproductive success
o
Fitness
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FRUIT FLY EXAMPLE
o
One fly carries the genes for a version of a trait that
allows it to survive a long time without food.
o
The other fly has the genes for a different version of
the trait that allows it to survive only a short while
without food.
o
Which fly has the greater fitness?
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THERE ARE THREE IMPORTANT ELEMENTS
TO AN ORGANISM’S FITNESS:
1.
An individual’s fitness is measured relative to other
genotypes or phenotypes in the population.
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THERE ARE THREE IMPORTANT ELEMENTS
TO AN ORGANISM’S FITNESS:
2.
Fitness depends on the specific environment in
which the organism lives.
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THERE ARE THREE IMPORTANT ELEMENTS
TO AN ORGANISM’S FITNESS:
3.
Fitness depends on an organism’s reproductive
success compared to other organisms in the
population.
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"SURVIVAL OF THE FITTEST" IS A
MISNOMER.
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THROUGH NATURAL SELECTION, POPULATIONS
OF ORGANISMS CAN BECOME ADAPTED TO
THEIR ENVIRONMENT.
Organisms in a population can become
better matched to their environment
through natural selection.
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ADAPTATION TO ENVIRONMENT
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THROUGH NATURAL SELECTION, POPULATIONS
OF ORGANISMS CAN BECOME ADAPTED TO
THEIR ENVIRONMENT.
Natural selection does not lead to
perfect organisms.
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
Evolution in general, and natural selection specifically,
do not guide organisms toward “better-ness” or
perfection.

If the environment changes, the alleles causing the
traits favored by natural selection may change, too.
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FACTORS THAT PREVENT POPULATIONS FROM
PROGRESSING INEVITABLY TOWARD
PERFECTION
1.
Environments
2.
Variation
3.
Multiple different alleles for a trait,
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THROUGH NATURAL SELECTION, POPULATIONS
OF ORGANISMS CAN BECOME ADAPTED TO
THEIR ENVIRONMENT.
Artificial selection is just a special case
of natural selection.
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ARTIFICIAL SELECTION
o
Animal breeders and farmers
o
Determined by humans and not nature,
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THROUGH NATURAL SELECTION, POPULATIONS
OF ORGANISMS CAN BECOME ADAPTED TO
THEIR ENVIRONMENT.
Natural selection can change the traits
seen in a population in several ways.
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DIRECTIONAL SELECTION
Individuals with one extreme from the range of variation
in the population have higher fitness.
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TURKEYS ON POULTRY
FARMS HAVE SUCH
LARGE BREAST MUSCLES THAT THEY CAN’T
GET CLOSE ENOUGH TO EACH OTHER TO MATE.
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STABILIZING SELECTION
Individuals with intermediate phenotypes are most fit.
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IS MEDICAL TECHNOLOGY UNDOING
THE WORK OF NATURAL SELECTION IN
OPTIMIZING THE NUMBER OF BABIES
WITH NORMAL BIRTH WEIGHTS?
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DISRUPTIVE SELECTION
Individuals with extreme phenotypes experience
the highest fitness, and those with intermediate
phenotypes have the lowest.
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NATURAL SELECTION CAN CHANGE
POPULATIONS IN SEVERAL WAYS:
1.
Directional selection,
2.
Stabilizing selection,
3.
Disruptive selection,
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MOST MAMMALS DO NOT DRINK MILK AFTER THEY ARE
WEANED BECAUSE THEY LOSE THE ABILITY TO DIGEST
LACTOSE.
THIS IS TRUE FOR ABOUT 60% OF PEOPLE.
BUT MOST PEOPLE OF NORTHERN EUROPEAN DESCENT
CAN DRINK MILK (AREAS WHERE DAIRY FARMING IS
HISTORICALLY PREVALENT). WHAT TYPE OF EVOLUTION
WOULD THIS EXEMPLIFY?
1.
2.
3.
Directed selection
Stabilizing selection
Disruptive selection
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THROUGH NATURAL SELECTION, POPULATIONS
OF ORGANISMS CAN BECOME ADAPTED TO
THEIR ENVIRONMENT.
Natural selection can cause the
evolution of complex traits and
behaviors.
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HOW CAN A WING EVOLVE IF 1% OF A
WING DOESN’T HELP AN ORGANISM FLY
OR GLIDE AT ALL?
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OFTEN, STRUCTURES
APPEAR BECAUSE
THEY SERVE SOME
OTHER PURPOSE.
FUNCTIONAL SHIFTS
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ADAPTING TO THE ENVIRONMENT
o
Natural selection can change allele frequencies for
genes involving roundabout unrelated paths.
o
A trait that has been selected for one function is
modified at a later time to serve a completely different
function.
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THE EVIDENCE FOR THE OCCURRENCE OF
EVOLUTION
1. The fossil record documents the
process of natural selection.
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RADIOMETRIC DATING
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THE EVIDENCE FOR THE OCCURRENCE OF
EVOLUTION
2. Geographic patterns of species’
distributions reflect their evolutionary
histories.
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BIOGEOGRAPHY
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THE EVIDENCE FOR THE OCCURRENCE OF
EVOLUTION
3. Comparative anatomy and embryology
reveal common evolutionary origins.
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CHICK EMBRYOS AND HUMAN EMBRYOS
BOTH HAVE GILLS BECAUSE…
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HOMOLOGOUS STRUCTURES
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ONTOGENY RECAPITULATES
PHYLOGENY
Why are we all born with one?
- Gills
- appendixes
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VESTIGIAL STRUCTURES
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CONVERGENT EVOLUTION
Analogous structures all
developed from different
original structures.
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WE CANNOT HIDE WHERE WE CAME
FROM
o
Similarities in how organisms look and develop shows
their common evolutionary origins.
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THE EVIDENCE FOR THE OCCURRENCE OF
EVOLUTION
4. Molecular biology reveals that
common genetic sequences link all life
forms.
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The genetic code provides our fourth line of
evidence that evolution occurs.
DNA SIMILARITIES AND DIFFERENCES
o
Related vs. unrelated individuals
o
The more distantly you and another individual are
related, the more your DNA differs.
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DNA SIMILARITY BETWEEN TWO SPECIES
o
Compare their DNA sequences for individual genes.
o
In Rhesus monkeys, 138 amino acids are the same as
those found in human hemoglobin.
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RECENCY OF COMMON ANCESTRY
o
Estimates of evolutionary
relatedness made from:
o Comparative Anatomy
o Embryology
o The Fossil Record
o
“Molecular Clocks”
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THE EVIDENCE FOR THE OCCURRENCE OF
EVOLUTION
5. Laboratory and field experiments
enable us to watch evolution in progress.
A fifth line of evidence for the occurrence of evolution
comes from multi-generation experiments and
observations.
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CHANGES IN THE FREQUENCY OF THE
VARIOUS ALLELES
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FIVE PRIMARY LINES OF EVIDENCE:
1.
The fossil record
2.
Biogeography
3.
Comparative anatomy and embryology
4.
Molecular biology
5.
Laboratory and field experiments
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