Download Lecture 13

Evolution
Pleistocene glyptodont
Do not
post on
Figure 17.5a
Page 276
Adaptation
What do these bugs
have in common?
A flower
mantid
in Malaysia
A leaf mantid in Costa Rica
Darwin’s Voyage
• Studied theology
• At age 22, 5yr, voyage on the Beagle
• Similarities between living and fossil
organisms
Figure 13.1A
Figure 13.4
Galapagos
Islands
Darwin
Wolf
Pinta
Genovesa
Marchena
Santiago
Bartolomé
Fernandia
Seymour
Baltra
Rabida
Pinzon
Santa Cruz
Santa Fe
Tortuga
San Cristobal
Isabela
Española
Floreana
Figure 13.5
Early Ideas
•Aristotle
•Judeo-Christian culture
•Lamarck
– Inheritance of acquired traits
Geology
• Geologists proposed…
– Very old Earth
– Changed by gradual processes
Descent with Modification
•Darwin and Wallace
•1859 On the Origin of Species
•Natural Selection
– The mechanism of evolution
– Artificial selection?
Artificial Selection
Hundreds to thousands
of years of breeding
(artificial selection)
Ancestral dog (wolf)
Figure 13.2A
Figure 13.2B
Natural Selection
Living species…
…Are descended from earlier forms
African wild dog
Coyote
Wolf
Thousands to
millions of years
of natural selection
Figure 13.2C
Ancestral canine
Fox
Jackal
Evidence for Evolution
•Fossils
A Skull of Homo
erectus
B Petrified tree
E Fossilized organic
matter of a leaf
C Ammonite casts
D Dinosaur tracks
F Insect in amber
G “Ice Man”
Figure 13.7
Evidence for Evolution
•The fossil record
– Time lines
Figure 13.3H
Evidence for Evolution
•Fossils link extinct species w/ living
species
Figure 13.3I
Evidence for Evolution
•Biogeography
– Geographic distribution of species
– Why are marsupials found mostly in
Australia?
Figure 13.10
Evidence for Evolution
•Comparative anatomy
– Homologous structures
•
Figure 13.4A
similar characteristics from common ancestry
Human
Cat
Whale
Bat
Evidence for Evolution
•Comparative Embryology
Pharyngeal
pouches
Post-anal
tail
Human embryo
Chick embryo
Figure 13.4B
Evidence for Evolution
•Molecular Biology
– Comparing DNA
between different
organisms
Table 13.4
Natural Selection
• Darwin’s observations
– Overproduction
– Individual variation
– Differential reproductive success
• Who will survive and reproduce?
Natural Selection
•Natural selection
– Certain traits increase survival
– Those indiv. influence the future
•Where can we observe changes in
traits?
Figure 13.14
Population Evolve
What is a population?
Population genetics
Populations Evolve
• Gene pool
– All genes in a population
• Sources of genetic variation
– Mutations
– Meiosis
– Fertilization
Populations Evolve
• Individuals don’t evolve!
• Evolution is change in frequency of
traits in a population!
Populations Evolve
• Or not?
•What would a nonevolving population look
like?
•Stable allele frequency
Hardy-Weinberg Equilibrium
– Genes are shuffled during sexual
reproduction
– does not alter the proportions of alleles
– P2 + 2pq + q2 = 1
Phenotypes
Genotypes
Number of animals
(total  500)
Genotype frequencies
Number of alleles
in gene pool
(total  1,000)
Allele frequencies
Figure 13.7B
WW
320
320  0.64
500
640 W
800  0.8 W
1,000
Ww
ww
160
20
160  0.32
500
160 W  160 w
20  0.04
500
40 w
200  0.2 w
1,000
Genetic Equilibrium
• No mutation
• Large population
• Isolation
• Everyone reproduces
• Random mating
Microevolution
• Drives a population away from
equilibrium: Natural selection
and…
– Gene flow
– Genetic drift
– Mutations
Genetic Drift
• Random fluctuation of allele frequencies
overtime
• More pronounced in small populations
Figure 13.22
Computer Simulation
1.0
AA in five populations
0.5
allele A lost
from four
populations
0
1
5
10
15
20
25
30
35
40
45
50
Generation
(25 stoneflies at the start of each)
Computer Simulation
1.0
0.5
allele A
neither
lost nor
fixed
0
1
5
10
15
20
25
30
35
40
45
Generation
(500 stoneflies at the start of each)
50
Bottleneck Effect
• A severe reduction in population size
• Lots of drift
• Example
– Elephant seals 20 individuals
– rebounded to 30,000
Bottleneck
Original
population
Bottlenecking
event
Figure 13.9A
Surviving
population
Figure 13.9B
Figure 13.24
Inbreeding
•
•
•
•
Leads to increased homozygosity
Can lower fitness
More recessive alleles are expressed
Amish, cheetahs
Founder Effect
• A few individuals start a new
population
• Allele frequencies of founders may be
different from original population
Figure 13.25
Gene Flow
• Genes move in/out of a population
• Immigration/emigration
• Minimizes genetic variation
between populations
Mutations
• Infrequent
– Lethal
– Neutral
– Advantageous
Natural Selection Revisited
• Largest impact
• Successful alleles = successful
phenotypes
• Who will reproduce?
• What will happen to allele frequencies?
• Increased fitness!
in the population
Number of individuals
Number of individuals
in the population
• Directional
Selection
Range of values for the trait at time 1
Range of values for the trait at time 2
Number of individuals
in the population
Natural
Selection
Revisited
Range of values for the trait at time 3
Antibiotic Resistance
• Since 1940s
• Overuse
• Resistant forms
Number of individuals
in the population
Natural
Selection
Revisited
Range of values for the trait at time 1
• Stabilizing
Selection
Range of values for the trait at time 2
Range of values for the trait at time 3
Number of individuals Number of individuals
in the population
in the population
• Disruptive
Selection
Range of values for the trait at time 1
Range of values for the trait at time 2
Number of individuals
in the population
Natural
Selection
Revisited
Range of values for the trait at time 3
Sexual Selection
Question of the Day
Antibiotic resistant bacteria are
showing up all over the place. The
infamous “flesh eating” bacteria is an
example. What are two things that
you can do to help prevent more
bacteria from becoming antibiotic
resistant?