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CHAPTER 15
Skim read pg. 418-422
EVOLUTION
15.1 Darwin’s Theory of Natural Selection
 Darwin on the HMS Beagle
 Darwin’s role on the ship was as naturalist and
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companion to the captain.
His job was to collect biological and geological
specimens during the ship’s travel
His visit to the Galápagos Islands help him form his
ideas about Natural Selection
Here he found a strange assortment of plants and
animals.
The islands are located 1000 kilometers West of South
America.
They are many islands all with different climates
because they all have different elevations.
The Galápagos Islands
 1.Darwin began to
collect mockingbirds,
finches, and other
animals on the four
islands.
 2.He noticed that the
different islands
seemed to have their
own, slightly different
varieties of animals
 3.At first nothing jumped
out at him as significant
but as he traveled back to
England he began to think
that the animals on the
different islands could
have once members of the
same species.
Darwin Continued His Studies After
Returning Home:
 Almost every specimen that Darwin had collected on the
islands was new to European scientists.
 He came to believe that populations of birds and animals
from the mainland (South America) changed after reaching
the Galápagos.
 Darwin hypothesized that new species could appear
gradually through small changes in ancestral species.
 Darwin inferred that if humans could change species by
artificial selection (such as, selecting cows that produce the
most milk for breeding) then perhaps the same process
could work in nature.
The Galápagos Islands
15.1 Darwin’s Theory of Natural Selection
 Natural Selection
 Individuals in a population have variations ( Tall/
Short)
 Variations can be inherited (Families tend to have
similar traits)
 Organisms that can survive on the available
resources will have offspring and will pass on their
traits
 Variations that increase reproductive success will
have a greater chance of being passed on.
The Origin of Species- written by Darwin
 Darwin published On the Origin of Species by Means
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of Natural Selection in 1859.
Darwin’s theory of natural selection does not have the
same meaning as evolution
It is a means of explaining how evolution works
At his time in history most Europeans believed that:
The Earth and all living creatures were divine creatures
put on Earth a few thousand years ago in just one week.
That all creatures have remained exactly as they were
when they were put on the Earth.
Natural Selection Video Clip
http://www.pbs.org/wgbh/evolution/educators/teach
studs/svideos.html
15.2 Support for Evolution
 1. The fossil record
 Fossils provide a record of species that lived long ago.
 Fossils show that ancient species share similarities with
species that now live on Earth.
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Glyptondt
Armadillo
Evidence of Evolution contin.
 2. Derived traits
are newly evolved features, such
as feathers, that do not appear in the fossils of
common ancestors
 3. Ancestral traits are more primitive features,
such as teeth and tails, that do appear in ancestral
forms
Homologous Structures
 4. Anatomically similar structures inherited from a
common ancestor are called homologous
structures.
5. Vestigial Structures
 Structures that are the
reduced forms of
functional structures in
other organisms.
 Evolutionary theory
predicts that features of
ancestors that no longer
have a function for that
species will become
smaller over time until
they are lost.
6. Analogous Structures
Analogous structures can be
used for the same purpose
and can look similar in
construction, but are not
inherited from a common
ancestor.
Show that functionally similar
features can evolve
independently in similar
environments
FLY
EAGLE
7. Comparative Embryology
http://www.pbs.org/wgbh/nova/evolution/guess-embryo.html
 Vertebrate embryos exhibit homologous structures
during certain phases of development but become
totally different structures in the adult forms.
8. Comparative Biochemistry
 Common ancestry can be seen in the complex
metabolic molecules that many different
organisms share.
Ch. 15.2 Continued……
15.2 Geographic Distribution
 The distribution of plants and animals that Darwin
saw on his voyage suggested that evolution had
occurred
15.2 Adaptation
 Adaptation is a trait shaped by natural selection that
increases an organism’s reproductive success.
 Fitness: is a measurement of the number of
reproductively viable offspring an organism
produces
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The better the organism is adapted to its
environment, the greater is chances of
survival and reproductive success
Adaptations for survival
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Poisonous
 Camouflage: adaptation
that allows the organism
to blend in with it
surroundings to avoid
getting eaten.
 Mimicry: One species
evolves to resemble
another species
 Both of this increases
survival- so the organism
will be able to reproduce
 Nonpoisonous
Mimicry and New Technologies
 http://www.nbcnews.com/tech/innovation/spider-
web-bandages-new-medicine-mimics-nature-n69141
15.3 Shaping Evolutionary Theory
 Mechanisms of Evolution
 Hardy-Weinberg principle states that when allelic
frequencies remain constant, a population is in
genetic equilibrium
Genetic Drift:
 A change in the allele frequencies in a population
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that is due to chance
In smaller populations, the effects of genetic drift
become more pronounced, and the chance of
losing an allele becomes greater.
Types of genetic drift:
1. Founder effect
2. Bottleneck
Founder Effect:
 Occurs when a small sample of a population settles in a
location separated from the rest of the population
 Alleles that were uncommon in the original population
might be common in the new population
 Example: Amish and Mennonite communities in the
U.S. rarely marry outside of their community.
 Higher incident of 6 fingered dwarfism.
 “Darwin’s Finches”
Bottleneck:
 Occurs when a
population declines to a
very low number and
then rebounds
 Example: Cheetah’s:
population declined 100
years ago and then
rebounded. The cheetahs
are so genetically
identically they appear
inbred. Can lead to
extinction due to an
increase of genetic defects
and a decrease in fertility
 Gene Flow:
 Is caused by the random movement if individuals
between populations. This increases genetic
variation within a population and reduces
differences between populations
 Nonrandom Mating: rarely is mating
completely random. Individuals usually mate with
other that are in close proximity. This can promote
inbreeding and lead to a change in allele frequency.
Mutations
 Mutations are the raw material for natural selection.
 Mutations occur randomly but can affect the allele
frequency in a population.
 Sometimes the mutation is harmful to a population
and sometimes it is helpful.
 Example: Giraffe's long necks
Natural Selection:
 Acts to select the individuals that are best adapted
for survival and reproduction
 Three types of Natural Selection:
1.
Stabilizing Selection:
2. Directional Selection
3. Disruptive Selection
1. Stabilizing Selection:
 Stabilizing selection operates to eliminate extreme
expressions of a trait when the average expression
leads to higher fitness. Example: human birth
weight- babies born with above-normal and below
– normal birth weights have a decreased chance
for survival
2. Directional Selection:
 Directional selection makes an organism more fit
 Example: The peppered moths- They existed in two
color forms (light and dark winged). When the
environment changed and favored the dark winged
moths, the light winged moths were more likely eaten
and they decreased in number.
3. Disruptive selection:
 Disruptive selection is a process that splits a
population into two groups and tends to remove
the individual with average traits
 Example: Size of beetles:
 Smaller than average can hide more easily. Larger
than average are more difficult to eat. Medium size
are more likely to be eaten.
Darwin added one more form
of Natural Selection:
Sexual selection operates in populations where
males and females differ significantly in
appearance.
 Qualities of sexual attractiveness appear to be the
opposite of qualities that might enhance survival
 Example: Peacock feathers seem as though it
would make it more difficult for the bird to flee
from a predator
Reproductive Isolation:
 Speciation: Is the process that some members of a
sexually reproducing population change so much
that they can no longer produce fertile offspring with
members of the original population.
 Two types:
 1. Prezygotic isolation: this prevents reproduction
through geographic, behavioral, ecological or other
differences. (before mating)
 Eastern and Western Meadowlark
Reproductive Isolation:
 2. Postzygotic isolation: after mating has occurred,
the hybrid individuals are not able to reproduce
themselves.
 Example: A tiger and lion can mate but the Liger
cannot reproduce (it is sterile)
 MATING OF A HORSE AND DONKEY PRODUCES
A MULE WHICH IS STERILE
• LIGER
WHAT MADE THIS?
Speciation:
 For speciation to occur the population must diverge
( separate)
 1.Allopatric speciation A physical barrier
divides one population into two or more
populations
Speciation:
 2. Sympatric Speciation: A species evolves into
a new species without a physical barrier.
 The original species and the new species live side
by side during the speciation process
 Example: Apple fly maggots are diverging based on
the type of fruit they eat
Adaptive Radiation
 Can occur in a relatively short time when one species
gives rise to many different species in response to the
creation of new habitat or some other ecological
Opportunity
• Often follows large-scale extinction events.
(Mammals following the extinction of the dinosaurs)
One species gave rise
to many new species
of cichlid fish
Coevolution:
 The relationship between two species might be so
close that the evolution of one species affects the
evolution of the other species.
 The two types of symbiotic relationships that are
often involved in coevolution are: Mutualism and
parasitism
 Example:
 A moth that gets food from a specific flower and in
turn pollinates that flower – both have coevolved to
create this relationship
Convergent Evolution:
 Unrelated species
evolve similar traits
even though they live
in different parts of
the world.
 Occurs when the
environments the
individuals live in are
similar even though
geographically they are
far apart
How Fast do evolution occur?
1. Punctuated
Equilibrium
2. Gradualism:
 Rapid evolution in
 Evolution occurs slowly
short periods of time &
some periods of time
when evolution occurs
slowly
over many, many years