Charles Darwin

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Charles Darwin
•
1859 – “Origin of Species”
published
1.
Argued from evidence that species
inhabiting Earth today descended from
ancestral species *****Descent with
modification explains life’s unity and
diversity
2.
Proposed a mechanism for evolution
 Natural Selection
In 1844, Darwin wrote an essay on the origin of species
and natural selection but did not introduce his theory
publicly, anticipating an uproar
In June 1858, Darwin received a manuscript from Alfred
Russell Wallace, who had developed a theory of natural
selection similar to Darwin’s
Darwin quickly finished The Origin of Species and
published it the next year
•Charles Darwin had a consuming interest in nature
•First studied medicine (unsuccessfully), and then theology at Cambridge University
•After graduating, he took an unpaid position as naturalist and companion to Captain Robert
FitzRoy for a 5-year around the world voyage on the Beagle
GREAT
BRITAIN
EUROPE
NORTH
AMERICA
ATLANTIC
OCEAN
The
Galápagos
Islands
AFRICA
Pinta
Genovesa
Equator
Marchena
Santiago
Fernandina
Isabela
Daphne
Islands
Pinzón
Santa
Santa
Cruz
Fe
Florenza
SOUTH
AMERICA
AUSTRALIA
PACIFIC
OCEAN
San
Cristobal
Cape of
Good Hope
Tasmania
Española
Cape Horn
Tierra del Fuego
New
Zealand
•During his travels on the Beagle, Darwin collected specimens of South American plants and
animals
•He observed adaptations of plants and animals that inhabited many diverse environments
•
The most influential stop on the voyage was to the Galápagos
Islands
•
Darwin noticed that many of the birds and reptiles were unique
to specific islands in the Galápagos archipelago
–
These included tortoises…
https://www.yout
ube.com/watch?
v=Gb_IO-SzLgk
•
In the
Darwinian
view, the
history of life
is like a tree
with
branches
representing
life’s diversity
•
Darwin’s
theory
meshed well
with the
hierarchy of
Linnaeus
Artificial Selection, Natural Selection, and
Adaptation
• Darwin noted that
humans have
modified other
species by selecting
and breeding
individuals with
desired traits, a
process called
artificial selection
https://www.youtub
e.com/watch?v=bi9
Pa0DHG5Y
• Darwin then
described four
observations of nature
and from these drew
two inferences
Fig. 22-9
Terminal
bud
Lateral
buds
Cabbage
Brussels sprouts
Flower
clusters
Leaves
Kale
Cauliflower
Stem
Wild mustard
Flowers
and stems
Broccoli
Kohlrabi
• Observation #1: Members of a population often
vary greatly in their traits
• Observation #2: Traits are
inherited from parents to
offspring
• Observation #3: All
species are capable of
producing more offspring
than the environment can
support
• Observation #4: Owing to
lack of food or other
resources, many of these
offspring do not survive
• Inference #1: Individuals whose inherited traits
give them a higher probability of surviving and
reproducing in a given environment tend to
leave more offspring than other individuals
• Inference #2: This unequal ability of individuals
to survive and reproduce will lead to the
accumulation of favorable traits in the
population over generations
An example of the process of evolution:
•
Some populations of head lice won’t be killed by the chemical permethrin, a
common treatment
•
Studies have shown that this evolution occurred after only about 30 months (40
generations of lice)
The Process of Evolution
• Individuals DO NOT evolve
– One louse did not, all of a sudden, have
the ability to stay alive when permethrin
was in the environment
– The resistance that developed was
genetic, passed on from one generation
to the next
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 22-12
(a) A flower mantid
in Malaysia
(b) A stick mantid
in Africa
Direct Observations of Evolutionary Change
• New discoveries continue to fill the gaps
identified by Darwin in The Origin of Species
• Examples provide evidence for natural
selection:
– Alcohol metabolizing flies
– evolution of drug-resistant HIV
– Antibiotic resistance in bacteria
– Pesticide resistance in insects
Fig. 22-14
100
Patient
No. 1
Patient No. 2
75
50
Patient No. 3
25
0
0
2
4
6
Weeks
8
10
12
Fig. 22-UN2
• Natural selection does
not create new traits, but
edits or selects for traits
already present in the
population
• The local environment
determines which traits
will be selected for or
selected against in any
specific population
There are 5 major pieces of evidence that
supports the theory of evolution
1. The Fossil Record
(a) Pakicetus (terrestrial)
• The fossil record
provides evidence of
the extinction of
species, the origin of
new groups, and
changes within
groups over time
(b) Rhodocetus (predominantly aquatic)
(c) Dorudon (fully aquatic)
https://www.youtube.com/watch?v=I2
C-3PjNGok
(d) Balaena
(recent whale ancestor)
Fig. 22-17
Homologous structures are anatomical
resemblances that represent variations on a structural
theme present in a common ancestor
2.
Humerus
Radius
Ulna
Carpals
Metacarpals
Phalanges
Human
Cat
Whale
Bat
Homologous Structures
• 3. Biochemical Evidence
– Molecular level  genes
shared among organisms
inherited from a common
ancestor
Fig. 22-18
Pharyngeal
pouches
Post-anal
tail
Chick embryo (LM)
Human embryo
4. Comparative embryology reveals anatomical
homologies not visible in adult organisms
5. Vestigial structures are remnants of features
that served important functions in the organism’s
ancestors
Natural Selection Does Not Result
in Perfection
• Natural selection
causes populations
to be more fit for
their environment,
not necessarily
“better” organisms
• Increased success
in one environment
does not mean
success in a
different
environment
Poisonous
bacteria
Natural Selection Results from
Current Environmental Conditions
Changing the population:
•
https://www.youtube.com/
watch?v=aTftyFboC_M
Directional selection – the traits move in a particular direction
–
i.e. toward higher metabolism rates; fast metabolizers in fruit flies
–
Horse evolution
Natural Selection Results from
Current Environmental Conditions
Stabilize the population:
•
Stabilizing selection – extremes are selected against and the traits of
the population remain the same because the average condition is the
most fit
–
i.e. birth weight of human babies (being very small or very large is not as
favorable)
Natural Selection Results from
Current Environmental Conditions
Splitting the population:
•
Diversifying selection – the average condition is the least fit
•
Increases the diversity – two or more variants are fit
–
i.e. HIV particles – better to evade the immune system
• Differences in
individuals arise
from differences in
their genes
• If DNA is mutated,
new alleles may
occur
• Natural selection
and evolution will
occur and the
mutation will survive
or die out
Biological Species Are Reproductively Isolated
• Alleles do not
spread among
different species
• Separate species
evolve differences,
such as lions and
leopards
• There is evidence of
a common ancestor
with spotted coat
– Allele for spots was
lost in lions but
maintained in
leopards
Biological Species Are Reproductively Isolated
•
Gene pool – all the alleles from all
the individuals in a species
•
Gene flow – the spread of an allele
through a species’ gene pool
–
•
A change in the frequency of an
allele in a gene pool – evolution of
that species
Gene flow does not occur between
different species
The Nature of Reproductive Isolated
•
If two organisms of different
species try to mate, no fertile
offspring will be produced
•
This is reproductive
isolation
•
Reproductive barriers to
reproduction take two general
forms…
–
–
Pre-fertilization
•
No attempt to mate
•
Or, no fertilized egg is
produced – if mating is
attempted
Post-fertilization
•
Mating does occur but
offspring either do not
survive or are sterile
The Nature of Reproductive Isolated
Pre-fertilzation barriers:
•
Spatial (habitat) isolation is
the most obvious
impediment to mating
–
•
The two species never
come into contact
Behavioral isolation is one
barrier to species that are
close in space
–
Differences in mating
behaviors
•
mating rituals, fireflies
blinking, birds songs
The Nature of
Reproductive Isolated
•
•
One example of behavioral
isolation can be see in the
blue-footed boobies
–
Male blue-footed boobies
have a mating dance to
attract females
–
Then the female engages
in pointing behavior with
the male
If the proper courting display
is not present, mating will not
occur
http://www.youtube.com/watch?v=lMbDjNDD4cM
http://www.youtube.com/watch?v=T2Bsu4z9Y3k&featur
e=related
The Nature of Reproductive Isolated
•
A barrier to mating resulting
from physical incompatibility
between sexual organs of two
different individuals is called
mechanical isolation
•
A barrier resulting from the
timing of reproduction is a
temporal isolation
–
Plants produce flowers at
different times of year
–
Cicadas
–
Eastern and western
spotted skunks
The Nature of
Reproductive Isolated
• Gamete
incompatibility is the
most common prefertilization barrier
– Mating does occur,
but the egg and
sperm are not
compatible
– Fertilization does
not occur
The Nature of Reproductive Isolated
Post-fertilization barriers:
•
Most interspecies hybrids
– offspring of parents from
two different species – do
not survive long after
fertilization
–
•
Incompatibility between
genes in different species
is the primary cause
In the case of some species,
such as horses and
donkeys, the difference in
genes is not so large, which
is why mules survive and
exist  sterile
The Process of Speciation
Speciation is the evolution
of one or more
species from an
ancestral form
Three steps are necessary
for one species to give
rise to another:
1.
Isolation of gene
pools of populations
2.
Evolutionary change
in gene pools
3.
Evolution of
reproductive isolation
preventing gene flow
Isolation & Divergence of Gene Pools
• Gene pools may become isolated if a small
population migrates to a location far from the
main population
Isolation & Divergence of Gene Pools
• The intrusion of a geologic barrier may also
isolate gene pools from each other
Isolation and Divergence of Gene
Pools
• Allopatric species:
isolated populations
due to barriers or
distance
• Sympatric species:
isolated by other
means –
populations are near
one another
The Evolution of Reproductive
Isolation
• The exact mechanism of the development of
reproductive isolation is still unknown
– When it occurs, the two species
follow different evolutionary paths
– The rapidity and course of different
forms evolving from a common
ancestor is a source of debate
between two hypotheses
The Evolution of
Reproductive Isolation
• Gradualism – an
accumulation of tiny
changes over millions of
years
• Punctuated
equilibrium – no
change for millions of
years and then drastic
changes that are fairly
quick (thousands of
years)
–
The fossil record seems
to support the
punctuated equilibrium
hypothesis
What is a species?
• The biological species
concept defines species
as a group of
individuals that can
reproduce with each
other, but not other
species
• Most commonly used
by biologists interested
in the process of
species formation
•
The genealogical
species concept
defines a species as the
smallest group of
reproductively
compatible organisms
containing all of the
known descendants of a
single common ancestor
–
This definition
emphasizes
evolutionary
lineages
–
Can be used with
asexual organisms
• Genealogical species
concept allows easier
identification
• If a population is
consistently different
from other populations,
it is a different species,
even if it can reproduce
with other populations
The Morphological Species Concept
•
Paleontologists use the
morphological species
concept to define a species – a
group of individuals that have
some reliable physical
characteristics distinguishing
them from all other species
–
They have a similar
morphology; look alike in
some key feature
•
Easy to use in practice on both
living and fossil organisms
•
Only a few key features needed
for identification
•
Fossils could represent different
ages and genders rather than
different species
Convergent Evolution
• Convergent evolution is
the evolution of similar, or
analogous, features in
distantly related groups
• Analogous traits arise
when groups
independently adapt to
similar environments in
similar ways
• Convergent evolution does
not provide information
about ancestry
Sugar
glider
Flying
squirrel
Changes in allele frequencies due to chance is
called genetic drift
Founder Effect
http://glencoe.mheducation.com/sites/0010122009/student_view0/cha
pter4/animation_quiz_-_simulation_of_genetic_drift.html
• Occurs when a small sample of a larger
population establishes a new population
• The sample’s gene pool differs from the
larger population’s
Population Bottleneck
• A dramatic but short-lived population size reduction
followed by a rapid increase is called a population
bottleneck
• Like the founder effect, it results in the new
population differing from the original
Genetic Drift in Small Populations
• Small populations are highly susceptible to
changes in allele frequency even by chance
• Humans have a long history of small
populations, and thus have been quite
vulnerable to genetic drift
Sexual Selection
• Mate preferences exist
in many populations
• When a trait influences
the likelihood of mating
the trait is under the
influence of sexual
selection, a form of
natural selection
–
Male peacocks have
large showy tails
–
Male lions have
dramatic manes
• Traits sometimes
appear to have not
relation to fitness
http://www.youtube.com/watch?v=VuQI8PsnuM&feature=related
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