Transcript natural selection

Chapter 12
FORCES of
EVOLUTIONARY CHANGE
Evolution & Populations
Evolution – a
descent
changewith
in allele
modification
frequency
• Calculation:
Descent – implies inheritance
• Modification – a change in heritable
number of copies of a particular allele
traits
from
toingeneration
total numbergeneration
of alleles present
the population
Microevolution
Population
= a group
= relative
of interbreeding
short-term
members
genetic
changes
of the same
withinspecies
a population or
species; the generation to generation
Gene pool
changes
in–allele
all the
frequencies
genes and their alleles
within a population
Evolutionary Thought
Buffon – suggested that closely related
species arose from a common ancestor
and changed as they spread
Lamark – suggested that organisms that
used one part of their body repeatedly
would increase their abilities, conversely
disuse of body parts would weaken an
organ until it disappeared; such changes
would pass to future generations
Charles Darwin:
The Voyage of the HMS Beagle
In the fourth
Ship’s
naturalist
year,aboard
the ship
the
ship, HMS
spent
a month
Beagle
in the
on its 5-year
voyage around
Galápagos
Islands
the coast of
South America
In the Galápagos Islands,
Recorded
Darwin
would
observations
form his theory
on the
results
of
evolution
of geological
by natural
forces
selection
and the fossils he discovered:
• Forest plant fossils mixed in
sea sediments
• Marine fossils found in a mountain cave
Charles Darwin:
The Influential Ideas
Lyell
• Principles of Geology –
natural processes are slow
and steady, and the Earth is
much older than 6000 years
idea
Malthus
• Essay on the Principles of Population –
individuals better able to obtain
resources were more likely to survive;
those that could not would die
Charles Darwin:
Darwin’s Finches
Different types of finch found
on the Galápagos islands
probably descended from a
single ancestral type
Gradually the finch population
branched in several directions, exploiting
the various resources each island offered
Charles Darwin:
Natural Selection
Descent with modification
Natural selection –
environmental factors cause
the differential reproductive
success of individuals with a
particular phenotype (genotype)
On the Origin of Species – 1859
The single, most powerful idea in biology
Modern Evolutionary Theory
The connection between natural selection
and genetics:
• Genetic mutations create heritable
variations
• This variation is the raw material upon
which natural selection acts
• DNA mutations occur at random in all
organisms
• Sexual reproduction results in
genetically different offspring
Figure 12.8
Natural Selection
What does
Adaptations
Elimination
Natural
selection
“Survival
of
add
phenotypes
to
does
reproductive
ofnot
the have
Fittest”
asuccess
goal
mean?
• Fitness
Adaptation
Natural
selection
– an=organism’s
any cannot
indirectly
featurereproductive
control
that
changes
provides
the
a selective
allele
mutation
contribution
frequencies
ofadvantage
genes
to theinnext
a because
population
generation
it
• Fitness
improves
Individuals
Natural
selection
depends
the
with
organism’s
poorly
on
cannot
theadapted
ability
generate
abilitytoto a
phenotypes
“perfect”
survive
and
just
organism
reproduce
long
are “weeded
enough to
out”
reproduce
• Natural
Individuals
Selected
selection
successful
with the
can
promotes
best
phenotypes
only
adaptations
work
any trait
with
are
are the
entirely
what
that
increases
is most
genetically
a matter
likely
anoforganism’s
to
available
thereproduce
time and
infitness,
a place
• even
The adaptations
(environmental
population
if that traitconditions
is
are
detrimental
passedundergo
ontotothe
the
offspring
change
organism’s
constantly)
survival
Generation1
Multiple generations later
Generation2
Antibiotic present
Time
Time
Staphylococcus aureus
before mutation
Mutation
occurs (red)
Reproduction
and
Selection
Antibiotic-resistant bacteria
are most successful
Hardy-Weinberg Equilibrium
Hardy-Weinberg
At
Hardy-Weinberg
equilibrium
equilibrium,
is aallele
highly
frequencies
unlikely
situation
and genotype
– it occurs
frequencies
only in
do
not change from
populations
that meet
generation
the following
to generation
assumptions:
• No
Allele
natural
frequency:
selection
• No mutations
number of copies of a particular allele
• Infinitely
large
population
total number
of alleles
present in the population
• Random mating
•• Genotype
frequency:
No movement
of individuals into or out
of the
population
number
of individuals with a particular genotype
total number of individuals present in the population
Figure 12.12
Hardy-Weinberg Equations
Dd
Dd
The equations
Two
equations provide
represent
a framework
the relationship
for
between allele
determining
whether
frequencies
evolution
and has
genotype
frequencies:
occurred;
in reality, allele frequencies
change when:
• Some
Allele frequencies:
phenotypes are better adapted
(natural selection)
• Mutations addp new
+ q =alleles
1.00
• Chance events occur
• Mating
Genotype
is selective
frequencies:
Allele Frequencies
• Individuals travel between populations
p2 + 2pq + q2 = 1.00
Dd
Dd
DD
Genotype Frequencies
DD
DD
dd
Dd
Dd
Dd
DD
dd
Dd
dd Female gametes
D
DD
d
DD
Dd
Dd
Male
Dd
gametes
Dd
DD
D
Dd
p2 = (0.6)2 = 0.36
DD
pq = (0.6)(0.4) = 0.24
dd
d
Dd
DD
pq = (0.6)(0.4) = 0.24
p2 + 2pq + q2 = 1
p = frequency of D (dominant allele) = dark fur = 0.6
q = frequency of d (recessive allele) = tan fur = 0.4
p+q=1
dd
q2 =
(0.4)2
DD
= 0.16
Figure 12.13
Natural Selection
Shapes Populations
Stabilizing selection
Directional
Disruptive
selection
selection–––two
intermediate
oneor
extreme
more
extreme phenotypes
phenotype
is fittest are fittest
Light
Small Medium
Dark
Large
Medium
Light
Dark
Pigmentation
Pigmentation
Birth weight
Health problems
Habitat
changes;
for
extremes
Habitat
changes;
mix
of light
trees
darken
and
dark
rocks
of individuals
Number
of individuals
Number
Number of individuals
Number of individuals
Number of individuals
Number of individuals
Directionalselection
Disruptive
Stabilizing
selection
Light
SmallLight
Medium
Dark
Medium Large
Dark
Pigmentation
Birth
Pigmentation
weight
Sexual Selection
Influences Reproductive Success
Sexual selection – a type of natural
selection resulting from variation in the
ability to attract a mate
• Members of the same sex compete
among themselves for mates
• Members of one sex choose particular
members of the opposite sex
Sexual dimorphism – a difference in the
appearance between males and females
of a species
Additional Mechanisms of Evolution
Mate selection
Mutation
Chance
events:
– a change
– a preference
in an organism’s
for a
•DNA
particular
Genetic
sequence
phenotype;
drift –introduces
a change
typically
in
a new
allele
a female
allele
into
selection
frequency
the population;
process
due to athe
chance
only source
event of
•new
Founder
allelesevent – occurs when a small
Migration
group is–isolated
members
from
entering
the home
and
interbreeding
population with an existing population
• Bottleneck
introduce
neweffect
alleles;
– occurs
departing
when
members
a
take
population
their alleles
decreases
with them
in number over a
relatively short period of time
Chapter 13
EVIDENCE of EVOLUTION
The Geologic Timescale:
4,600 – 248 MYA
Permian
248 First conifers; fewer amphibians, more reptiles; cotylosaurs
and pelycosaurs; Pangaea supercontinent forms
290
Paleozoic era
Phanerozoic eon
Carboniferous
Reptiles arise; ferns abundant; amphibians diversify;
first winged insects
354
Bony fishes, corals, crinoids; amphibians arise,
land plants and arthropods diversify
Devonian
417
First vascular plants and terrestrial
invertebrates; first fish with jaws
Silurian
443
Ordovician
Algae, invertebrates, graptolites, jawless fishes;
first land plants
490
“Explosion” of sponges, worms, jellyfish, “small shelly
fossils”; ancestors of all modern animals appear; trilobites
Cambrian
Precambrian
supereon
543
Eukarotes appear; O2from photosynthesis accumulates
in atmosphere
Proterozoic eon
2,500
Archean eon
Life starts
3,800
Hadean eon
4,600
Earth forms
The Geologic Timescale:
248 MYA – Recent
Recent
Quaternary
Human civilization
0.01
Homo sapiens, large mammals; ice ages
Pleistocene
1.8
Cenozoic era
Australopithecus ,modern whales
5.3
Hominoids; mammals continue to diversify;
modern birds; expansion of grass lands
Miocene
23.8
Tertiary
Oligocene
Elephants, horses; grasses
33.7
Mammals and flowering plants continue to
diversify; first whales
Eocene
54.8
Paleocene
First primates; mammals, birds, and pollinating insects diversify
65
Widespread dinosaurs until extinction at end of Cretaceous;
first flowering plants; present-day continents form
Cretaceous
Mesozoic era
Phanerozoic eon
Pliocene
144
First birds and mammals; cycads and ferns abundant;
giant reptiles on land and in water
Jurassic
206
Triassic
248
First dinosaurs; first mammals; therapsids and thecodonts;
forests of conifers and cycads
Fossil Record Evolution:
Often the Record is Incomplete
Only animals with hard body parts are
fossilized
Geological activity destroys many
preserved specimens
Fossils buried deep in the Earth or
submerged in the depths of the oceans
will likely never be discovered
Figure 13.4
Fossil Record Evolution:
Estimating the Age of Fossils
Absolutedating
Relative
dating
• Uses
Placesradiometric
fossils in adating
sequence
to assign
of events
an
without
age
to a assigning
fossil by testing
a specific
the age
fossil itself
• or
Presumes
the sediment
that lower
in which
rockitstrata
was found
are
• Radioactive
older than higher
isotopes
layers
decay at
• characteristic
Relative method
and
ofunchangeable
determining rates
• Half-life
“oldest”=tothe
“most
timerecent”
it takes for half the
atoms in a radioactive sample to decay
Living organism
After death
Organism
incorporates
12C and 14C.
14C
leaves
as 14N.
No new
12C or 14C
added.
14C
leaves
as 14N.
14C
12C
After death,
proportion of
carbon as 14C
declines.
Figure 13.5
Biogeography:
The Theory of Plate Tectonics
Today MYA
Earth’s
280-200
181-135
100-65
surface
MYA
consists of several rigid
layers, called tectonic plates
• Where the plates collide, mountain
ranges are formed
• Where plates separate, new molten
rock seeps to Earth’s surface
Two
All continents
Present-day
Continents
major
are
continents
joined into
continue
toform.
form
one
drift
supercontinent,
and
apart.
begin to drift
Pangaea.
apart.
North
North
America.
America
Europe
Africa
South
South
America
America
Asia
Eurasia
Laurasia
India
Africa
India
Australia
Australia
Antarctica
Antarctica
Figure 13.6
Biogeography:
Species Distribution
Fossil distribution indicates that the
continents were
once part of a
super continent
Africa
India
South
America
Australia
Antarctica
Biogeography:
Species Distribution
The rise and fall of marsupials
• Diverse and abundant in South America
until about 1 or 2 MYA
• Invading placental mammals out
competed the marsupials
• Marsupials remain in Australia because
its isolation kept them free of
competition
Figure 13.7
Biogeography:
Species Distribution
Wallace’s Line:
• Alfred Russel Wallace noticed a unique
assemblage of animals on either side of
an imaginary line in the Malay
Archipelago
• “Wallace’s line” is a deep-water trench
that separated the islands
• The water barrier prevented migration
between populations; evolution
produced a unique variety of organisms
on each side of the Wallace’s line
Asia
Philippines
Africa
Australia
Malay
Peninsula
Borneo
Sumatra
New
Guinea
Sulawesi
Java
Wallace’s line
Indian Ocean
More like Asia
Australia
More like Australia
Figure 13.8
Anatomical Comparisons:
Homologous Structures
Homologous structures have similarities
that indicate common ancestry
Homologous structures share a common
ancestry, but may function differently
Figure 13.9
Anatomical Comparisons:
Vestigial Structures
Vestigial structures have no apparent
function in one organism, but appear to
be homologous to a functional structure
in another species
Anatomical Comparisons:
Convergent Evolution
Convergent evolution – the evolution of
similar adaptations in organisms that do
not share the same evolutionary lineage,
but encountered similar selection
pressures
Analogous structures – similar function
but not in structure because of
convergent evolution, not descent from a
common ancestry (e.g. a bird’s wing vs.
an insect’s wing)
Figure 13.13
13.12
13.11
Embryonic Development
Indicates Common Ancestry
Homeotic
The
Vertebrate
fetal skull
genes
embryos
a expressed
appear alike
unequally
in early
Chimpanzee
Human
chimpanzee
development
result
in different
and
, reflecting
aanatomy
similar
development
human have
processes
asthe
cells divide and
same parts, but
differentiate
follow different
developmental
pathways
Area of gene
expression
Forelimb
Homeotic gene A
Homeotic gene B
Forelimbs
develop
into wings
Forelimbs
absent
Flank
Flank
Fish
Mouse
Hindlimb
Hindlimb
Chick
Hindlimbs
develop
into legs
Python
Alligator
Hindlimbs
remain
vestigial
Figure 13.14
Molecular Evidence:
Comparing DNA & Protein Sequences
Cytochrome c Evolution
DNA and protein similarities
• It is highly unlikely that two unrelated
species would evolve precisely the
same DNA and protein sequences
• It is more likely that the similarities
were inherited from a common ancestor
and the differences arose through
mutation
Organism
Number of amino acid
differences from humans
Chimpanzee
0
Rhesus monkey
1
Rabbit
9
Cow
10
Pigeon
12
Bullfrog
20
Fruit fly
24
Wheat
37
Yeast
42
Figure 13.15
Molecular Evidence:
Molecular Clocks
Molecular clock
• Uses a know mutation rate for a gene
and the number of differences in the
DNA sequences for that gene in two
species
• Estimates the time when the organisms
diverged from a common ancestor
~ 50 million years later
~ 25 million years later
G AC T T A G A C T
G A C T T GG A C T
Common ancestor
DNA sequence
Modern species 1
G A C T T G G A C T
Common ancestor
G A C T T A G G C T
G A C T T AG G C T
50 MYA
~ 25 million years later
~ 50 million years later
G A C C T AG G C T
G A C C T A G G C C
25 MYA
Today
Modern species 2
G A C C T A G G C C
Chapter 14
SPECIATION and EXTINCTION
Species Names
Carolus Linnaeus – assigned species a
two-word biological name
• Genus – a broader classification
• Specific term
For example, the human biological name
is Homo sapiens
• Genus – “Homo”
• Specific term – “sapiens”
Biological Species Concept
A species is a population, or group of
populations, whose members can
interbreed and produce fertile offspring
Does not apply to:
• Asexually reproducing organisms
• Extinct organisms
• Organisms that would only interbreed
in captivity
• conditions when reproductive isolation
is not absolute
Speciation
The formation of new species – occurs
when some individuals can no longer
successfully interbreed with the rest of
the population
• Reproductive isolation - the two groups
could not produce fertile offspring
• Macroevolution = large-scale
evolutionary change
Figure 14.3
Reproductive Isolation:
Prezygotic Reproductive Barriers
Habitat – different environments
Prezygotic Reproductive Isolation
Barrier
Description
Example
Illustration
Temporal – active or fertile at different
times
Habitat
isolation
Different
environments
Ladybug feed
on different
plants
Temporal
isolation
Active or fertile
at different times
Field crickets
mature at
different rates
Behavioral
isolation
Different
courtship
activities
Frog mating
calls differ
Mechanical
isolation
Mating organs
or pollinators
incompatible
Sage species
use different
pollinators
Behavioral – different courtship rituals
Mechanical – mating organs or
pollinators incompatibility
Sea urchin
gametes are
incompatible
Gametic – gametes cannot unite
Gametic
isolation
Gametes cannot
unite
Figure 14.3
Reproductive Isolation:
Postzygotic Reproductive Barriers
Hybrid inviability – hybrid offspring fail to
reach maturity
Postzygotic Reproductive Isolation
Barrier
Description
Example
Hybrid
inviability
Hybrid offspring fail to
reach maturity
Hybrid eucalyptus
seeds and seedlings
are not viable
Hybrid infertility
(sterility)
Hybrid offspring
unable to reproduce
Lion-tiger cross
(liger) is infertile
Hybrid
breakdown
Second-generation
hybrid offspring have
reduced fitness
Offspring of hybrid
mosquitoes have
abnormal genitalia
Illustration
Hybrid infertility (sterility) – hybrid
offspring is unable to reproduce
Hybrid breakdown – second-generation
hybrid offspring have reduced fitness
Figure 14.4
Spatial Patterns
Define Two Types of Speciation
Allopatric speciation
• Geographic barrier separates a
population into two groups that can no
longer contact one another
• Natural selection and
genetic drift act
independently on
each
group resulting in
eventual reproductive
isolation
No contact between populations
Figure 14.4
Spatial Patterns
Define Two Types of Speciation
Sympatric speciation
• Reflects the fact that a habit that
appears uniform actually consists of
many microhabitats
• Organisms may
specialize to different
zones resulting in
eventual reproductive
isolation
Continuous contact between populations
Figure 14.9
The Pace of Speciation
Gradualism = one species transforming
into another through a series of small,
incremental changes over many
generations
Gradualism
Punctuated equilibrium
Punctuated equilibrium = long periods of
little change interrupted by relatively brief
bursts of rapid evolutionary change
Time
Extinction
Extinction = the complete disappearance
of a species
• Background extinction rate = steady,
gradual loss of species through natural
competition or the loss of genetic
diversity
• Mass extinction = great numbers of
species disappear over a relatively
short expanse of time
Precambrian
Mesozoic
Paleozoic
Cenozoic
Total extinction rate
(families per million years)
20
15
10
5
0
600
400
Time (MYA)
200
0
Taxonomy & Taxonomic Hierarchy
Taxonomy = the study of describing,
naming, and classifying organisms
• Systematics = the study of
classification
• Phylogenetics = the study of
evolutionary relationships among
species
Carolus Linnaeus – organized life into a
hierarchical classification system
Linnaean Taxonomic Hierarchy
Linnaean classification of the plant
Aloe vera (in descending order):
Taxonomic group
Aloe vera plant found in:
Number of species
Domain
Eukarya
Several million
Kingdom
Plantae
~375,000
Anthophyta
~235,000
Class
Liliopsida
~65,000
Order
Liliales
~1200
Family
Asphodelaceae
785
Genus
Aloe
500
Species
Aloe vera
1
Phylum
Figure 14.14
Cladistics
Cladogram– –the
Phylogenetic
Outgroup
tree-like
system
basis that
for
diagram
comparison
defines
thatgroups
infer
in
by evolutionary
cladistic
an
distinguishing
analysis
relationship
to
between
determine
ancestral
whichand
derived characters
characters
are ancestral and which are
• Ancestral character = an inherited
derived
attribute that resembles that of the
Clade
ancestor
= a group of organisms consisting
• Derived
of
a common
character
ancestor
= aand
feature
all ofnot
its found
descendants
in the ancestor
Clades
Birds
Non-avian
dinosaurs
Crocodiles
Node (common ancestor)
Lizards
and snakes
Turtles
Last common
ancestor
Mammals
Amphibians
“Traditional” Groups Are Not Clades
Traditional groups such as endotherms
(“warm-blooded” animals) refers to a
character of convenience and does not
make reference to the common ancestor
of all endothermic animals