Chapters 15, 16, and 17
Evolution
The Theory of Evolution
Theory – well-tested explanation that
unifies a broad range of observations
Evolution – change in a kind of organism
over time; process by which modern
organisms have descended from ancient
organisms
Can theories change over time?
Are theories supported scientifically?
Charles Darwin – 1831 Voyage
of the Beagle
Darwin studied:
Diversity – he
found a wide range
of living things
well adapted to
their environment
Fossils – he was
curious as to why
some were extinct
Ground Sloth Fossil
Galapagos Islands
Volcanic islands off the west coast of South
America
Unique species found nowhere else in the
world
How did this
happen?
Galapagos
Galapagos
Darwin Returns Home
After Darwin returned home, he studied his
notes and specimens
He struggled with his observations and how
they conflicted with his religion
He finally published On the Origin of
Species, a book which outlined his theories
of natural selection and evolution over time
Darwin’s Influences:
James Hutton and Charles Lyell –
Geologists whose theories suggested that
Earth was extremely old and was always
changing slowly over time.
Darwin proposed that living things were not
fixed in one form, but also changed slowly
over time.
Darwin’s Influences:
Jean-Baptiste
Lamark – proposed
the theory of
acquired
characteristics
Use or
disuse…some traits
were passed down
to help survival of
offspring
False theory
Darwin’s Influences
Thomas Malthus – an English economist
who studied human population growth
He believed that if humans became
overpopulated, they would struggle to
survive without sufficient resources
Darwin applied this to animals and plants
and believed it was the driving force for
evolution.
Darwin studied variation
Darwin did not know about genes, but did
observe traits being passed on
Artificial selection – when humans choose
which traits are to be passed on in animals
and plants by selective breeding
Examples: Breeds of dogs, pidgeons, cows,
corn, Brassica oleraceae
Darwin proposed Natural Selection
The idea that there is a struggle for
survival…need to find food, mates, run
away, hide, or protect themselves
Darwin proposed that some individuals
were better adapted for their environment
Adaptation - any inherited characteristic
that increases an organism’s chance of
survival
“SURVIVAL of the FITTEST”
Adaptations:
Descent with Modification
Darwin proposed
Descent with Modification
Living things changed over long periods of
time due to natural selection
He believed that living things evolved from
a “common ancestor”
“Tree of life” links all living things
Darwin’s early drawing of a tree
of life…
Evidence of Evolution:
The fossil record
Evidence of Evolution
Geographic
distribution of living
things – different
animals on different
continents looking
similar (marsupial
wolf and grey wolf)
Animals that are not
closely related have
similar adaptations
Evidence of Evolution
Homologous Structures – structures that
have different mature forms but develop
from the same embryonic tissues.
Vestigial organs
remnants of
legs in skinks,
appendix in
humans…
Evidence of Evolution
Similarities in Embryology
Pattern of Evolution
Coevolution: the change in two or more
species in close association with each other
Ex: Plants and their pollinators
Patterns of Evolution Cont’d
Convergent Evolution
Organisms appear similar, but are not related
The environment selects similar phenotypes
Ex: streamlined body of dolphins and sharks
Patterns of Evolution Cont’d
Divergent Evolution
Two or more related
species become more and
more dissimilar
• Can result in new species
Response to differing
habitats
Adaptive radiation: many
related species evolve
from a single ancestral
species
Chapter 16 –
Evolution of Populations
Evolution in genetic terms – any change in
the relative frequency of alleles in a
population.
Gene pool – all genes (T, t) present in a
population
Relative frequency – number of times one
allele appears compared to all alleles in the
gene pool. (Example: B = 40%, b = 60%)
The population is evolving if the frequency
changes
Gene Pool
allele for
allele for
brown fur
black fur
Sources of Genetic Variation:
Mutations – a change in the sequence of
DNA. Caused by chemicals, radiation, or
just randomly. Can be harmful, helpful, or
have no effect.
Gene shuffling – genes are recombined
during the formation of gametes for sexual
reproduction. Does not change gene
frequencies on its own.
How many genes control one trait?
Single Gene and Polygenic Traits
If a trait is controlled by one gene it is
called a single-gene trait.
Single-gene traits result in only two
phenotypes. Example: Tall or Short
Polygenic traits result in a range of
phenotypes. Example: height of a human
being.
Which graph represents a
polygenic trait?
Polygenic traits continued…
Directional Selection
Polygenic traits continued…
Stabilizing selection
(Example:
Birth weight)
Polygenic traits continued…
Disruptive selection
Example: Beak Size
Genetic Drift
Genetic drift is a random change in gene
frequency.
Common in small populations
Founder effect – a small group migrates
away from the original group and has a
unique gene pool
Examples: Galapagos, Hawaii..
Hardy-Weinberg principle
If a population does not evolve, it is in
genetic equilibrium. It must:
1. Have random mating
2. Consist of a large population
3. No members move in or out of the group
4. Have no mutations
5. No natural selection occurs
Example? Coelacanth?
Speciation
Species – a group of
organisms that can
breed with one another
and have fertile
offspring
Speciation –
formation of a new
species due to natural
selection or chance
events
Isolating Mechanisms
In order for new
species to evolve,
groups of organisms
must be separated or
isolated.
If the two groups
change enough, and
can no longer breed
and create fertile
offspring, then new
species were formed.
Causes of reproductive isolation Geographical isolation – Groups are
physically separated.
Ecological isolation- Groups occupy
different habitats.
Temporal isolation- reproduce at different
times of the day.
Behavioral isolation- no attraction.
Mechanical isolation- structural differences.
Reproductive failure- no fertile offspring.
Speciation in Darwin’s Finches:
17-2 Earth’s Early History and
17-4 Patterns of Evolution
Earth is about 4.6 billion years old
Earth’s early atmosphere probably
contained:
Hydrogen cyanide
Carbon dioxide
Carbon monoxide
Nitrogen
Hydrogen sulfide
Water
Where did organic compounds
come from?
1950s – Stanley Miller and Harold Urey
designed experiments that showed organic
compounds could be formed from elements
in Earth’s early atmosphere if an electric
current was introduced
Lightning could provide the electric current
Amino acids, cytosine, and uracil could be
formed in these experiments.
Miller/Urey’s experiment
Mixture of gases
simulating
atmospheres of
early Earth
Spark simulating
lightning storms
Cold water
cools
chamber,
causing
droplets to
form
Liquid
containing
amino acids
and other
organic
compounds
Organic molecules to cells?
Organic molecules can form tiny bubbles
called proteinoid microspheres, almost like
oil in water
RNA may have been the first hereditary
material, as it can self-replicate and act as
catalysts.
These components may have been the first
primitive cells…but the exact origin of life
is a MYSTERY!
Early Bacteria created Oxygen
Cyanobacteria (blue
green algae) were
probably the first
living things to
manufacture oxygen
Oxygen changed the
atmosphere, turned the
sky blue, and allowed
organisms to respire
aerobically (more
efficient)
Endosymbiotic Theory
Eukaryotic cells may have formed when
larger cells engulfed smaller prokaryotes
Mitochondria and chloroplasts may have
been free-floating bacteria
Evidence: They have DNA and ribosomes
similar to bacteria and reproduce by binary
fission
The ability to respire aerobically and the
ability to reproduce sexually increased
diversity and influenced evolution
Endosymbiotic Theory
Other Topics:
Fossils and ancient life
Index fossils
Radioactive dating
Geologic time scale
Evolution of
multicellular life
Mass extinctions
Patterns of Evolution
Macroevolution – large scale evolutionary
patterns and processes over long periods of
time
Extinction
Adaptive Radiation
Convergent Evolution
Coevolution
Punctuated Equilibrium
Changes in developmental genes
Extinction
When a species no longer exists on earth
Most extinctions were natural until recent
times
Can be gradual for individuals or can be
catastrophic mass extinctions that affect
multiple life forms
Scientists believe an asteroid impact caused
a mass extinction event in the Cretaceous
Adaptive Radiation
When a single species or small group of
species evolve into many diverse forms
over time.
Examples: Mammals evolved, finches
evolved
Convergent evolution
When unrelated
organisms that live in
similar environments
develop similar
adaptations to survive
Coevolution
The process by which
two species evolve in
response to changes in
each other over time
Punctuated Equilibrium
Long, stable periods with little change in
species interrupted by brief periods of rapid
change
Results from small populations, isolated
populations, following mass extinctions…
Developmental Genes and Body Plans
In some cases, small
changes in just a few
genes can cause major
changes in an
organism
Hox genes are “master
control” genes for
animal body plans
One change in a gene
can lead to wingless,
one pair, or two pairs