copyright © 2003 pearson education, inc. publishing as benjamin cummings –varieties of life forms...
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Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
– Varieties of life forms
Figure 1.4C-F
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• All organisms have evolutionary adaptations
– Inherited characteristics that enhance their ability to survive and reproduce
• blue-footed booby
• Large, webbed feet help propel the bird throughwater at high speeds
Clown, Fool, or Well Adapted?
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– A streamlined shape, large tail, and nostrils that close are useful for diving
– Specialized salt-secreting glands manage salt intake while at sea
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• Charles Darwin synthesized the Theory of Evolution by natural selection
– Theory vs hypothesis
• Evolution is the core theme of biology
Evolution explains the unity and diversity of life
Figure 1.6A
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• The voyage of the Beagle
Figure 13.1B
NorthAmerica
Great Britain Europe
Africa
Equator
Australia
Tasmania
NewZealand
Cape ofGood Hope
SouthAmerica
An
des
Cape Horn
Tierra del Fuego
GalápagosIslands
PacificOcean
AtlanticOcean
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• species are fixed
• Earth is about 6,ooo yrs old
Prevalent ideas at Darwin’s time
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New ideas proposed
• Fossils indicated the earth was very old
• Lyell, a geologist, argued that land forms changed constantly.
• Lamarck proposed that organisms changed and these changes were passed to progeny.
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• Darwin became convinced that the Earth was old and continually changing
– He concluded that living things also change, or evolve over generations
– He also stated that living species descended from earlier life-forms: descent with modification
• Mex. marine snail shells on high mtns
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• Darwin observed that
– organisms produce more offspring than the environment can support
– organisms vary in many characteristics
– these variations can be inherited
Darwin proposed natural selection as the mechanism of evolution
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• natural selection explains the mechanism of evolution
Figure 1.6B
(1) Population with varied inherited traits
(2) Elimination of individuals with certain traits
(3) Reproduction of survivors
Pesticide-resistant insects
Antibiotic-resistant bacteria
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• Charles Darwin, 1874
Figure 13.1x2
• Alfred Wallace
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• Darwin cartoon
Figure 13.1x3
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• Evolution happens when populations of organisms with inherited variations are exposed to environmental factors that favor the reproductive success of some individuals over others–Natural selection is the editing mechanism
–Evolution is based on adaptations
Figure 1.6C
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– Hominid skull
Fossils provide strong evidence for evolution
Figure 13.2A, B
– Petrified trees
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– Ammonite casts
– Fossilized organic matter in a leaf
Figure 13.2C, D
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– Scorpion in amber
– “Ice Man”
– acid bogs
Figure 13.2E, F
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• Mammoth tusks
Figure 13.2x4
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• fossils show that organisms have appeared in a historical sequence
• Many fossils link early extinct species with species living today
– hind leg bones of fossil whales
Figure 13.2G, H
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– Biogeography
– Comparative anatomy
– Comparative embryology
Other evidence for evolution
Figure 13.3A
Human Cat Whale Bat
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– Molecular biology - protein “clocks”
Figure 13.3B
Human Rhesus monkey Mouse Chicken Frog Lamprey
Last commonancestor lived26 million yearsago (MYA),based onfossil evidence
80 MYA
275 MYA
330 MYA
450 MYA
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Populations are the units of evolution
Figure 13.6
1.What is evolving? gene pool, microevolution
2.Four agents of evolution
3. Types of natural selection
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Populations are the units of evolution
• A population is a group of interbreeding individuals
• A species is a group of populations whose individuals can interbreed and produce fertile offspring
Figure 13.6
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• gene pool = total collection of genes in a population at any one time
• Microevolution is a change in the relative frequencies of alleles in a gene pool
What is evolving?
Four agents of microevolution
1. Mutation changes alleles
2. Genetic drift = random changes in allele frequency Bottleneck
Founder effect
LARGE POPULATION = 10,000 SMALL POPULATION = 10
allele frequency =1,00010,000 = 10% allele frequency =
110 = 10%
50% of population survives,including 450 allele carriers
50% of population survives,with no allele carrier amongthem
allele frequency =4505,000 = 9% allele frequency =
05 = 0%
little change in allele frequency(no alleles lost)
dramatic change in allele frequency(potential to lose one allele)
Genetic drift - effects of population size:
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Founder effect
Figure 13.11B, C
Bottleneck effect
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3. Gene flow can change a gene pool due to the movement of genes into or out of a population
ex. Migration
4. Natural selection leads to differential reproductive success
Nonrandom mating changes genotype frequencybut not allele frequency.
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• Natural selection
- results in the accumulation of traits that adapt a population to its environment
- the only agent of evolution that results in adaptation.
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Darwinian fitness is an individual’s contribution to the gene pool of the next generation compared to other individuals; i.e., number of progeny
• Production of fertile offspring is the only score that counts in natural selection
What is an organism’s evolutionary fitness?
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There are three general outcomes of natural selection
Figure 13.19
Fre
qu
en
cy
of
ind
ivid
ua
ls
Originalpopulation
Phenotypes (fur color)
Originalpopulation
Evolvedpopulation
Stabilizing selection Directional selection Diversifying selection
beak depth
1976
1978Averagebeak depth,1978
Averagebeak depth,
1976
Beak depth (mm)
Shift of average beakdepth during drought
5 6 7 8 9 10 11 12 13 140
20
40
60
80Number of individuals
Infantdeaths
Infantbirths
Percentof infantdeaths
Percent ofbirths inpopulation
Birth weight in pounds
0
10
20
30
40
50
60
70
2 3 4 5 6 7 8 9 10 11880
5
10
15
20
Natural selection tends to reduce variability in populations.
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1. The diploid condition preserves variation by “hiding” recessive alleles (Bb)
2. Balanced polymorphism (2+ phenotypes stable in population) may result from:
a. heterozygote advantage Aa > aa and AA
b. frequency-dependent selection
c. variation of environment for a population
Why doesn’t natural selection eliminate all genetic variation in populations?
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• Many populations exhibit polymorphism and geographic variation
Figure 13.13
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3. Some variations may be neutral, providing no apparent advantage or disadvantage
– Example: human fingerprint patterns
Not all genetic variation may be subject to natural selection
Figure 13.16
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• Low genetic variability may reduce their capacity to survive as humans continue to alter the environment
– cheetah populations have extreme genetic uniformity
Endangered species often have reduced variation
Figure 13.17
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• Sexual selection leads to the evolution of secondary sexual characteristics
• Sexual selection may produce sexual dimorphism
Why do male and female animals differ in appearance?
Figure 13.20A, B
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• This is due to:
– historical constraints
– adaptive compromises
– chance events
– availability of variations
Natural selection cannot fashion perfect organisms
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• appearance alone does not always define a species
Figure 14.1A
– Example: eastern and western meadowlarks
What is a species?
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What is a species?
• Naturally interbreeding populations
- potentially interbreeding
- reproductively isolated from other species
What about asexually reproducing organisms?
Extinct species?
Shy species?
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• When geographically isolated, species evolution may occur
– gene pool then changes to cause reproductive isolation
= allopatric speciation
When does speciation occur?
MECHANISMS OF SPECIATION
Figure 14.3
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• A ring species may illustrate the process of speciation
Figure 14.1C
OREGONPOPULATION
1
2
COASTALPOPULATIONS
Yellow-eyed
Monterey3
SierraNevada
Yellow-blotched
Gap in ring Large-
blotched
INLANDPOPULATIONS
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Reproductive barriers between species
• Habitat - different locations
• Timing - mating, flowering
• Behavioral - mating rituals, no attraction
• Mechanical - structural differences
• Gametic - fail to unite
• Hybrid weak or infertile
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• Hybrid sterility is one type of postzygotic barrier
– A horse and a donkey may produce a hybrid offspring, a mule
– Mules are sterile
Figure 14.2C
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Sympatric speciation
• No geographical isolation
• Mutation creates reproductive isolation
• Polyploidization
• Hybridization
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• Specialists - Galapagos finches
• Generalists - horseshoe crabs, cockroaches
• New environments
- ecological niche
When does speciation occur?
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• Adaptive radiation on an island chain
- specialization for different niches
Figure 14.4B
Species Afrom mainland
1
A
2B
B
3BC 4
C
C5
BC
D
C D
Figure 15.9
Mediumground finch
Cactusground finch
Smalltree finch
Largeground finch
Smallground finch
Large cactusground finch
Sharp-beakedground finch
Vegetarianfinch
Seedeaters
Ground finches
Cactus flowereaters
Budeaters
Tree finches
Insecteaters
Mediumtree finch
Largetree finch
Mangrovefinch
Woodpeckerfinch
Greenwarbler finch
Graywarbler finch
Warbler finches
Common ancestor fromSouth America mainland
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• Continental drift is the slow, steady movement of Earth’s crustal plates on the hot mantle
Continental drift has played a major role in macroevolution
Figure 15.3A
PacificPlate
NorthAmerican
Plate
NazcaPlate
SouthAmerican
Plate
AfricanPlate
EurasianPlate
Splitdeveloping
Indo-AustralianPlate
Edge of one plate being pushed over edge of neighboring plate (zones of violent geologic events)
Antarctic Plate
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• influenced the distribution of organisms
– Continental mergers triggered extinctions
– Separation of continents caused the isolation and diversification of organisms
Figure 15.3B
Mil
lio
ns
of
ye
ars
ag
o
EurasiaCE
NO
ZO
ICM
ES
OZ
OIC
PA
LE
OZ
OIC
North America
AfricaIndiaSouth
America
AntarcticaAustra
lia
Laurasia
Gondwana
Pangaea
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Speciation - how much change is needed?
• Gradual vs. jerky
• Evidence:
– Fossil record
– Genetic differences between species
– Homeotic genes
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• homeotic genes control body development
• Single mutation can result in major differences in body structure
Figure 11.14
Mouse chromosomes
Mouse embryo (12 days)
Adult mouse
Fly chromosomes
Fruit fly embryo (10 hours)
Adult fruit fly