Adaptations
Mesophyll
cell
Night
CO2
4-C compound
CO2
4-C compound
CO2
CO2
CALVIN
CYCLE
CALVIN
CYCLE
Bundlesheath
cell
3-C sugar
3-C sugar
Day
C4 plant
CAM plant
Evolution
Ch 13
Charles Darwin
1874
1859
Voyage of the HMS Beagle
On the Origin of Species…
• Descent With
Modification
• By means of Natural
Selection
How Did Darwin Come Up With
His Ideas?
• Scientific Method
• Key observations
– Traits vary in a population
– Most traits are inherited from parent to offspring
– More offspring are produced than the
environment can support (Thomas Malthus)
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, more fit individuals tend to
leave more offspring than less fit
individuals.
• Natural Selection is the mechanism
– Reproduction (differential) is Key
Darwin’s Theory of Evolution
• Natural Selection is the mechanism
– Reproduction (differential) is Key
• Fitness- degree of adaptation to a specific
environment
• Adaptive if it enhances individual’s fitness
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
Support for Descent with
Modification
•
•
•
•
Biogeography
Fossil Record
Molecular Biology, Biochemistry, Cell Biology
Comparative Anatomy
Biogeography
• Geographic distribution of species
– 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
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 through time
• 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
•
•
•
•
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
•
May reduce the capacity of endangered species to
survive as humans continue to alter the
environment
Figure 13.10
Selection Models
Sexual Selection
• Sexual Dimorphism
• Sexual Selection- where individuals with
certain characteristics are more likely to
obtain mates than others.
– Intrasexual selection
– Intersexual selection
Selection
• Heterozygote advantage
– Balancing selection
• Ex: Sickle cell anemia
– Frequency-dependent selection
• Fitness of genotype depends on frequency it occurs
• Ex: mimicry
– Neutral Variation
• Little to no impact on phenotype or fitness
• Natural Selection cannot distinguish alleles
Natural Selection is Limited
•
•
•
•
Only act on existing variation
Historical constraints
Compromise
Chance, selection and the environment