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Evolution
Ch 13
Historical Theories
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Anaximander (~2500 yrs ago)
Aristotle
Georges Buffon (1700’s)
Jean Baptist Lemark (late 1700’s - early1800’s)
Erasmus Darwin
Charles Darwin
1874
1859
Voyage of the HMS Beagle
On the Origin of Species…
• Descent With
Modification
• By means of Natural
Selection
Support for Descent with
Modification
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Biogeography
Fossil Record
Molecular Biology, Biochemistry, Cell Biology
Comparative Anatomy
Biogeography
• Geographic distribution of species
– Darwin noted that Galápagos animals resembled
species of the South American mainland more
than animals on similar but distant islands
– Organisms may have common ancestor
Fossil Evidence
– Organisms evolved in a historical sequence
A Skull of Homo
erectus
D Dinosaur tracks
B Petrified tree
C Ammonite casts
E Fossilized organic
matter of a leaf
G “Ice Man”
F Insect in amber
Figure 13.3A–G
Fossil Evidence
Many fossils link early extinct species with species
living today
Figure 13.3I
Comparative Anatomy
• Comparison of body structures in different species
– Homology- similar characteristics resulting from common
ancestry
– Homologous structures- features with different functions
but structurally similar due to common ancestry
Figure 13.4A
Human
Cat
Whale
Bat
Comparative Embryology
•Comparison of early stages of development
among different organisms
Pharyngeal
pouches
Post-anal
tail
Human embryo
Chick embryo
Figure 13.4B
Molecular Biology
•Comparisons of DNA and
amino acid sequences
between different
organisms to reveal
evolutionary relationships
Table 13.4
How Did Darwin Come Up With
His Ideas?
• Scientific Method
• Key observations
– Traits vary in a population & most are inherited
from parent to offspring
– More offspring are produced than the
environment can support (Thomas Malthus)
Trait Variation
Recap
• Limited resources
• Overproduction of offspring
• Heritable individual variation
– Therefore, survival depends partly on inherited
features
Darwin’s Theory of Evolution
• In a varied population, individuals whose
inherited characters best adapt them to the
environment are more likely to survive and
reproduce.
• Therefore, they tend to leave more
offspring than less fit individuals.
• Natural Selection is the mechanism
– Reproduction (differential) is Key
Natural Selection
Artificial Selection
Observing natural selection
• Camouflage
adaptations that
evolved in different
environments
A flower
mantid
in Malaysia
A leaf mantid in Costa Rica
Figure 13.5A
Pestacide Resistance
Chromosome with gene
conferring resistance
to pesticide
Pesticide application
Survivor
Additional
applications of the
same pesticide will
be less effective, and
the frequency of
resistant insects in
the population
will grow
Figure 13.5B
Antibiotic resistance
Colorized
SEM 5,600
•The excessive use of antibiotics is leading to the
evolution of antibiotic-resistant bacteria
Figure 13.13
Natural Selection Experiment
• Darwin Finches
(Galapagos Finches)
• Similar EXCEPT for
beaks
– Beaks = specialization
Unit of Evolution
•Evolution acts on individuals, affects
whole populations
–Populations are the unit of evolution
– Group of individuals of the same species living in
the same place at the same time
Unit of Evolution
• Evolution is change in prevalence of heritable
traits in population
• A gene pool
– Is the 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
Hardy-Weinberg Equilibrium
• Frequency of alleles in a stable population
will not change over time
– Very large population
– Population is isolated
– Mutations don’t alter gene pool
– Random mating
– All individuals are equal in reproductive success
• In reality, this never happens
Agents of Change
• Genetic Drift
– Bottle neck affect
– Founder affect
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Gene Flow
Mutation
Non Random Mating
Natural Selection
Variation
•Extensive in most populations
•Mutation and sexual recombination generate variation
and can create new alleles.
Figure 13.11
Endangered species often have
reduced variation
• Low genetic variability
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May reduce the capacity of endangered species to
survive as humans continue to alter the
environment
Figure 13.10
Types of Selection
Sexual Selection
• Sexual Dimorphism
• Sexual Selection- where individuals with
certain characteristics are more likely to
obtain mates than others.
– Intrasexual selection
– Intersexual selection
Diploidy
• Heterozygote advantage
• Balancing selection
• Frequency-dependent selection
Natural Selection is Limited
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Only act on existing variation
Historical constraints
Compromise
Change, selection and the environment