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Chapter 10: Evolution
Introduction
• 2 million species on Earth that have been given a
scientific name
• Many more unidentified species: 5 million, 10
million?
• How many species have gone extinct?
• Organisms today may represent less than 1% of all
life forms that have ever existed
• How life has changed over time and how we make
sense of the living work around is the focus.
• Understanding the mechanisms by which species
evolve by natural selection is one of the most
important and influential concepts in biology
I.
Evidence for Evolution
A. Charles Darwin: naturalists that took a 5 year trip
around the world on the HMS Beagle in1831 and
observed diverse and unique organisms
1. Galapagos Islands: noticed that
groups of animals varied from island
to island (finches and tortoises)
2. Noticed similarities and differences among
animals around the world
3. Darwin took years to put together his evidence
for a theory of evolution and his theory forms the
basis for modern thoughts on evolution by natural
selection
Darwin
Section 15-1
Giant Tortoises of the Galápagos
Islands
Pinta
Pinta Island
Tower
Marchena
Intermediate shell
Fernandina
James
Santa Cruz
Isabela
Santa Fe
Hood Island
Floreana
Isabela Island
Dome-shaped shell
Hood
Saddle-backed shell
Galapagos’s Tortoise
• Galapagos's tortoise can
live for over 150 years
• Eat plants
• Different shells
depending on the island
B. Alfred Wallace: another scientist that
developed the same idea of evolution in 1858.
1. Darwin and Wallace presented their ideas
jointly to the Linnean Society in 1858
C. What is evolution?
1. Evolution: process of cumulative change in the
heritable characteristics of a population
a) Heritable: changes must be passed
on genetically from one generation to
the next: doesn’t happen overnight
b) Cumulative: stress the fact that one
change is usually not enough to have a major
impact on a species
c) Population: changes do not affect just
one individual Evolution
2. Speciation: new species arises if enough
changes occur in a population and they can no
longer interbreed
3. Evidence for evolution by natural selection
a) Fossil records
b) Animal breeding
c) Homologous structures
d) DNA evidence: some contradictions to
evolution but also provided new support for
natural selection
4. Modern synthesis or neo-Darwinism:
combination of Darwin’s ideas with a newer
one, Mendel genetics
a) Darwin couldn’t explain how traits
were passed down
b) Mendel was working on his pea
experiments for heredity (1856-1863)
c) Darwin never read Mendel’s work
d) Not until the 1900’s did the two ideas
come together to show how natural
selection and heredity worked together
D. Fossil record and evolution
1. Fossils: petrified remains or traces of
animals and plants
2. Fossil record: accumulation of evidence
from these remains and traces such as
skeletons and footprints
3. Paleontologists have been collecting and
classifying fossils in an organized fashion for
almost 200 years.
4. Discoveries that provide evidence for evolution
a) Life that existed more than 500 million
years ago was vastly different in appearance
form life today
b) Although Earth has had oceans for most
of its existence, fish fossils have only been
found in rocks 500 million years old or younger
c) Most top predators today are mammals, but
not of them existed at the time of dinosaurs or
before
d) Majority of living organisms today have
no similar form in the fossil record except for
sharks, cockroaches, and ferns
5. Conclusion from studying fossils: Life on
Earth is constantly changing and changes have
occurred over huge timescales (hundreds of
thousands or millions of years)
6. Ageing fossils: Age of a rock can be determined
by carefully examining differences in the ratios
of isotopes
a) Isotopes: versions of atoms that are heavier
or lighter than other versions of the same atom
(carbon-14 has more mass than carbon-12)
b) If a fossil of a bone has a high level of
carbon-14, it is younger than a bone that has a
very low level of carbon-14
c) Carbon-14 (14C) is radioactive and
changes its identity into another atom,
nitrogen-14
d) Decay: process of a radioactive parent
isotope changing into a stable daughter isotope
e) Half-life: time it takes for half of the parent
isotope to decay into a stable daughter isotope
f) Ratio of radioactive 14C to stable 14N is used
to determine the age of a fossil
E. Artificial selection and evolution
1. Fossil record is incomplete, but breeding
domesticated animals provides a good record
of change in heritable characteristics
2. Breeders have learned to choose the males
and females with the most desirable genetic
characteristics and breed them together
3. Artificial selection: human select which
animals will reproduce in order to get desired
traits
F. Homologous structures: anatomical structures similar
in form but are found in seemingly dissimilar species
and show that they had a common ancestor
1. Example: Pentadactyl limbs (penta-five, dactylfingers) is found in many diverse animals
a) Shape and number of bones may vary, but
the general format is the same
b) Limb may have very different functions in
each animal
c) Suggested that all five fingered organism
have a common ancestor Homologous
G. Species divergence: two populations of a
species have diverged (separated) and a new
species has evolved from an old one
1. Both species will then continue on their
separate ways
2. If there is a significant difference in two
populations then they can no longer
interbreed and are two differed species
H. Adaptive radiation: occurs when many
similar but distinct species evolve relatively
rapidly from a single species or from a small
number of species
1. Occurs when variations within a
population allow certain members to exploit
a slightly different niche in a more successful
way
2. Niche: position or role within a
community of an ecosystem
3. A new species can evolve by natural selection
and the presence of a barrier
a) Barrier separating a population could be a
mountain range or body of water
4. Example: Primates found in Madagascar and
Comoro Islands off Africa
a) Millions of years ago, lemurs were able to
grow to large number due to the lack of
competition from monkeys or apes
b) Large numbers of offspring meant a
greater diversity of traits
c) Today, there are many different species of
lemur with different specialties due to
adaptive radiation
i) Some are adapted for living in trees and
some on the ground
ii) Some are adapted for living in rainforest
and others in the desert
iii) Most are active during the day (diurnal),
but some are nocturnal
d) Lemurs are found today only on these
islands, but fossils have been found in Africa,
Europe, and Asia
e) Lemurs were probably not successfully in
competing with apes and monkeys
f) Continents and islands tend to either have
prosimians (lemurs) or anthropoids (monkeys
and apes) but not both types of primates
5. Example: Finches on the Galapagos Islands
a) Probably was one species of finch that
evolved into 13 different species of finch
b) Different beak shapes allowed them to
each different food on different islands
I. Continuous variation and gradual divergence
1. Figure shows that species A,B,C and D
come from a common ancestor, but they are
now separate species that could not produce
fertile offspring
2. Some species can have various splits over time and
create greater diversity between species that no longer
resemble each other anymore
3. Within a species that has a wide geographical
distribution, there can be measurable difference in
DNA
a) Climate and soil are different
b) Populations adapt to the conditions
available and some versions of genes will be
selected for and others will be selected against
so that the populations are best adapted to their
areas (Selective pressure)
c) If the differences between the two
separated populations become too great, then
they will become separate species
J. Transient polymorphism
1. Polymorphisms: different versions
of a species that can be the result of a mutation
2. Example: Peppered moth (Biston betularia)
a) Peppered (grey) form: camouflaged against
light surfaces like trees with lichens
b) Melanic (black) form: rare mutation 1% of
population and easily seen against light colored
lichen and are eaten by birds
c) During the mid 1800’s in the industrial revolution:
melanic form increased in number
i) Lichen was sensitive to air pollution
produced by the industrial revolution and they
began to die
ii) Air was filled with black
soot from burning coal
iii) Camouflage of the peppered form of the
moth was no longer working since the trees
were now darker
d) Melanic form (carbonaria) had reached 95100%
e) Today the melanic form doesn’t go above 30%
and is often close to 0% due to improvements
in air quality since 1956.
f) Transient polymorphism: temporary
changes in the form of a species (light moth to
dark moth and back to light moth)
Note: Read Theory of Knowledge box on p. 228.
Discuss questions.
II. Natural Selection: mechanism for evolution
suggested by Darwin and Wallace
A. Natural selection: process by which
individuals that are better adapted to their
environment survive and reproduce more
successfully than less well adapted
individuals Natural selection
B. Steps of Darwin’s reasoning for natural selection
1. Overproduction of offspring
2. Natural variation in the population (Genetic
variation)
3. Struggle to survive
4. Differential survival: best fit survive better
5. Reproduction
C. Overproduction: Too many offspring
1. Plants and animals produce more offspring
than could ever survive
2. Maximizes the chances of some offspring
surviving
D. Struggle to survive: Too many offspring and not
enough resources creates competition for these
resources
E. Genetic variation
1. Asexually reproducing organisms like
bacteria has little chance for DNA modification
2. Sexually reproducing organisms produce
slightly different offspring each time which
can lead to a wide variety of offspring in a
population
3. Variation is closely related to how successful
an organism is
a) How frequent an allele is can change over
time because of changes in the environment
and is possible if there is more than one form
of the allele
b) When there is a change in the
environment, a variation in a species will
allow some to survive while others may die
c) Variation is strength in a population
4. In asexually reproducing populations where all
members are identical, there are just two outcomes:
survival or death
a) Great Famine in Ireland was caused by a water
mold that infected the potatoes. The potatoes were
all produced asexually and were all susceptible to the
blight
b) More variety leads to more possible outcomes
where some survive, some survive with negative
effects, some die
c) Variety allows some individuals to be better
adapted to changes in the environment that may be
harmful to others
F. Mechanisms for variation: Mutation, meiosis, sexual
reproduction
1. Mutation in DNA
a) Disadvantage: mutations can produce genes
that lead to disease
b) Advantage: beneficial adaptations that allows
the organism to survive
c) Neutral: effects are neither useful or harmful
d) In each generation, only a few genes may mutate
2. Meiosis: production of 4 haploid gamete cells
(egg/sperm)
a) Each gamete is genetically different from each
other and only contains 50% of the parent cell’s
genome
b) Produces huge numbers of possible
combinations of half the genetic material
c) Radom orientation during metaphase I
promotes variety in the gametes
d) Crossing-over during prophase I further
increases the genetic variety Twins
3. Sexual reproduction: sperm and egg cell must
be present at the same moment
a) Some chance involved
b) Increases variety in the population
G. Adapt
1. Adaptations by natural selection:
unconscious changes made by populations
and not individuals
2. Fit: organism that has characteristics that
are well adapted for its environment
3. Natural selection tends to eliminate from a
population individuals that show low fitness and
the fittest individuals have higher likelihood of
surviving
Example: Giraffe necks
H. Adaption and survival
1. Evolution is not just based on chance:
which individuals survive is determined by
their surroundings and the compatibility of
their characteristics with those surroundings.
Steps of evolution by natural selection
1. Overproduction of offspring and they have
natural variation as a result of genetic
differences
a) Useful variations allow some to have a
better chance of survival
b) Harmful variations make it difficult to
survive
2. Individuals with genetic characteristics that are
poorly adapted tend to be less successful at
obtaining resources and surviving
3. Individuals that are well adapted have a better
fitness
4. Individuals that survive to adulthood have a
better chance of reproducing and passing on
their successful genetic characteristics to the
next generation
5. Over many generations, the accumulation of
changes in the heritable characteristics of a
population results in evolution: gene pool has
changed
Darwin called these ideas “ survival of the fittest”
III. Natural selection and the frequency of
characteristics:
Modern examples of evolution that have occurred
rapidly
A. Pesticide resistance in rats
1. Farmer applies pesticide to field to kill the
rats
2. Due to natural variation,
a few rates are slightly different
and are not affected by the poison
3. Resistant rats are better adapted to survive
in the presence of the pesticides and now
there are fewer rats to compete with for food.
They thrive and reproduce, making a new
population which some are resistant to the
pesticide
4. Farmer puts out more of the original
poison and fewer rats die since poison
resistance is now favored
5. To kill the resistant rats, a new pesticide
must be used
Notes for this example:
1. Resistance is a change that evolves in a population
from one generation to the next
2. Immunity develops within the lifetime of an
individual and is not the case with the rats.
3. Rat is either born with the susceptibility to be
killed by the pesticide or is born with a resistance
to it
4. Individual rat cannot adapt and evolve into a
resistant rat
5. Characteristics that change and evolve over
time must be passed on by genes: Characteristics
acquired during an organisms' lifetime cannot be
passed on to the next generation and is not a part
of natural selection
B. Antibiotic resistance in bacteria
1. Antibiotics: medications like penicillin that kill
or inhibit the growth of bacteria
a) Give to patients with bacterial infections
b) Does not work on viral diseases
2. Steps of antibiotic resistance in bacteria
a) Patient gets a bacterial infection like tuberculosis
b) Doctor prescribes antibiotics to kill the bacteria
c) Gets better because most of the bacteria are destroyed
d) Due to a genetic modification some bacteria are resistant to the
antibiotic
e) Bacteria is not killed and it can now multiply and make the
patient sick again
Goes back to the doctor for the same antibiotic, but doesn’t get
better
g) Doctor has to prescribe a stronger antibiotic and hopes that it
works
f)
3. Reasons why the bacteria have developed
resistance
a) Overuse of antibiotics for nonbacterial
diseases
b) Not finishing the prescribed amount of
antibiotics
Resistance
4. Sources of change in the genetic makeup of
bacteria
a) Mutations
b) Plasmid transfer: one
bacterium donating genetic
information to another bacteria
by the use of a plasmid
(ring of DNA)
5. Solutions
a) Finding new antibiotics
b) Minimize use of antibiotics when they are
not needed
c) Finish the entire course of antibiotics
when prescribed
6. Examples of resistance
a) New strains of syphilis: show multiple
resistance
b) Tuberculosis: resistant to 9 different
antibiotics
c) MRSA: Methicillin resistant
Staphylococcus aureus: staph infection that
is often found in hospital settings