Download BILD 10.LECTURE 8.Hochmuth.2014

ANNOUNCEMENTS – Thursday February 13, 2014
Chapter 8: Evolution and Natural Selection
• Dr. Traver returns next week.
• Movie on Tuesday afternoon – “What Darwin Never Knew”.
• Midterm 2 is next week 2/20/2014
• I will be back to moderate the debate on
Tuesday 2/25/2014. Please contact
Dr. Traver if you would like to sign up.
Use new chapter opening photo here
Darwin’s dangerous idea: evolution by natural
selection
Learning objectives
•  By the end of today’s topic students
should be able to:
–  identify four agents of evolutionary change
and describe how they contribute to changes
in allele frequencies in a population.
–  explain the three conditions required for
evolution by natural selection to occur.
–  list five primary lines of evidence of evolution
and give an example of each.
Evolution in Action
We can see evolution occur
right before us.
Could you breed fruit
flies who could live
longer than 20 hours
on average?
When these eggs hatch, do you think the
flies in this new generation will live longer
than 20 hours without food?
What happened?
q 
Evolution
•  A genetic change in the population
q 
Natural selection
•  The consequence of certain individual organisms in
a population being born with characteristics that
enable them to survive better and reproduce more
than the offspring of other individuals in the
population
Does evolution occur?
q  The
answer is an unambiguous YES.
q  We
can watch it happen in the lab
whenever we want.
Evolution
q  How
does evolution occur?
q  What
types of changes can cause
evolution in a population?
q  Five
primary lines of evidence
q  Evolution
by natural selection
Darwin’s Journey to an Idea
Before Darwin, most people
believed that all species had been
created separately and were
unchanging.
Jean-Baptiste Lamarck
q  Biologist,
q  Living
early 1800s
species might change over time.
Charles Lyell
q  Geologist
q  1830
book Principles of Geology
•  Geological forces had shaped the earth and were
continuing to do so.
q  Gradual
but constant change
A job on a ‘round-the-world survey
ship allowed Darwin to indulge and
advance his love of nature.
q  Age
16, University of Edinburgh, medical studies
q  Studied
q  His
theology at Cambridge University
real love: study of nature
Observing geographic similarities and
differences among fossils and living
plants and animals, Darwin developed a
theory of evolution.
q  Lyell’s
q  The
Principles of Geology
Galapagos Islands
The Galapagos Islands
Two important and unexpected patterns:
1. Traits exhibited by species
2. Similarity between the fossils of extinct
species and the living species in that same
area
q  Glyptodonts
The Book that Would
“Rock the World”
Thomas Malthus
q  Economist
q  Essay
and armadillos
on the Principle of Population
q  1842
q  Darwin
realized that favorable variations
are preserved.
q  14
first draft
years in a drawer
In 1859, after decades of
mulling and procrastinating,
Darwin published his thoughts
on natural selection.
q  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.
q  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.
Poll Time
•  Cheetahs (large African cats) are able to
run faster than 60 miles per hour when
chasing prey. How would a biologist
explain how the ability to run fast evolved
in cheetahs, assuming their ancestors
could run only 20 miles per hour?
Individuals do NOT evolve.
Four mechanisms can give
rise to evolution.
q  Populations
q  Allele
Evolution occurs when the
allele frequencies in a
population change.
q  It
evolve
frequencies
is helpful to think of each allele as
having some “market share” of all of the
alleles.
Natural Selection
q  An
efficient mechanism of evolution…
q  …and
a powerful force in adapting
populations to their environment
Agents of Evolutionary Change
1.
2.
3.
4.
Mutation
Genetic drift
Migration
Natural selection
q  Evolution
and natural selection, however,
are not the same thing.
Evolution is genetic change in a population.
Mutation—a direct change in the DNA of
an individual—is the ultimate source
of all genetic variation.
Mutation is the
ultimate source of
genetic variation in a
population.
BUT only when
mutated genes are
present in the
germline!
What causes mutations?
q  The
process of cells dividing can go awry.
q  Environmental
phenomena
•  Mutagens
q  Mutations
are random
•  Beneficial?
•  Detrimental?
Genetic drift is a random
change in allele frequencies
in a population.
Nearly all mutations reduce an
organism’s fitness.
q  Suppose
paper.
that you have written a ten-page
q  Randomly
select one letter in the paper
and change it to another letter.
q  Is
the change more likely to make your
paper better or worse?
Fixation
The important factor that
distinguishes genetic drift from
natural selection:
The change in allele frequencies is not
related to the alleles’ influence on
reproductive success.
q  Genetic
drift can lead to fixation for one
allele for a gene in a population.
q  If
this happens, there is no more
variability in the population for this gene.
q  Genetic
drift reduces the genetic
variation in a population.
Founder Effect
Two special cases of genetic drift, the
founder effect and population
bottlenecks, are important in the
evolution of populations.
q  A
small number of individuals may leave a
population and become the founding
members of a new, isolated population.
q  The
founders may have different allele
frequencies than the original “source”
population, particularly if they are a small
sample.
Why are Amish people more likely to
have extra fingers and toes?
The impact of genetic drift is
much greater in small
populations than in large
populations.
Population Bottlenecks
Migration into or out of a population
may change allele frequencies.
The third agent of evolutionary change
When three simple conditions are
satisfied, evolution by natural selection
occurs.
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.
Condition 1: Variation for a Trait
q  Variation
is all around us.
q  Variation is the raw material on which
evolution feeds.
Condition 2: Heritability
We call the transmission of traits from parents to
their children through genetic information
inheritance or heritability.
Condition 3: Differential
Reproductive Success
1.  There are more organisms born than can
survive.
Condition 3: Differential
Reproductive Success
3.  Some organisms are more likely to win
this struggle and survive and reproduce.
Condition 3: Differential
Reproductive Success
2.  Organisms are continually struggling for
existence.
Differential Reproductive Success
From all the variation
existing in a population,
individuals with traits
most suited to
reproduction in their
environment generally
leave more offspring than
individuals with other
traits.
Reproductive Success
Traits causing some individuals to
have more offspring than others
become more prevalent in the
population.
q  Fitness
•  A measure of the relative amount of
reproduction of an individual with a
particular phenotype, compared with the
reproductive output of individuals of the
same species with alternative
phenotypes
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.
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.
There are three important elements to
an organism’s fitness:
2.  Fitness depends on the specific
environment in which the organism lives.
Organisms in a population can become
better matched to their environment
through natural selection.
Natural selection does not lead to
perfect organisms.
Why doesn’t natural selection
lead to the production
of perfect organisms?
Factors that Prevent Populations from
Progressing Inevitably Toward Perfection
1.  Environments change quickly.
2.  Variation is needed as the raw material of
selection.
3.  There may be multiple different alleles for a
trait, each causing an individual to have the
same fitness.
Artificial selection is just a special
case of natural selection.
q  Because
the differential reproductive success
is determined by humans and not nature,
this type of natural selection is also called
artificial selection.
Natural selection can change the
traits in a population in several
ways
Directional Selection
Individuals with one extreme from the range
of variation in the population have higher
fitness.
Turkeys on poultry farms have such large
breast muscles that they can’t get close
enough to each other to mate.
How can such a trait evolve?
Stabilizing Selection
Individuals with intermediate phenotypes are most fit.
Disruptive Selection
Individuals with extreme phenotypes experience the
highest fitness, and those with intermediate phenotypes
have the lowest.
Natural selection can cause the
evolution of complex traits and
behaviors.
How can a wing evolve if 1% of a
wing doesn’t help an organism fly or
glide at all?
Often, structures
appear because they
serve some other
purpose.
Functional Shifts
The evidence for
evolution is
overwhelming.
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
Five primary lines of evidence:
1.  The fossil record
2.  Biogeography
3.  Comparative anatomy and embryology
4.  Molecular biology
5.  Laboratory and field experiments
The fossil record documents
the process of natural
selection.
Comparative anatomy and
embryology reveal common
evolutionary origins.
Homologous Structures
Vestigial Structures
Convergent Evolution
Analogous structures
all developed from
different original
structures.
Molecular biology reveals that
common genetic sequences link
all life forms.
The genetic code provides our fourth
line of evidence that evolution occurs.
http://www.bababrinkman.com/video/