EVOLUTION BY MEANS OF NATURAL SELECTION
EVOLUTION BY MEANS OF NATURAL SELECTION
change of populations of organisms
The process by which all organisms have
developed from older forms of life
Old species go extinct (mass extinction)
and new species arise.
A group of organisms similar in structure
and heredity capable of producing fertile
*breeding within the species…always
exceptions to every rule…
*Originate from non-living matter
Once Life is here…evolution can occurevolution
and develop over time.
Abiotic synthesis of small, organic molecules (amino
acids, nitrogenous bases)
◦ “prebiotic soup”, no free O2 + lightning + volcanoes = molecule
+ Clay from volcanic ash
Making macromolecules… proteins, nucleic acids
Origin of self replication
inheritance …RNA or DNA?
◦ First genetic material- RNA, ribozymes-catalytic RNA
(ribosomes); protein synthesis
Anaerobic Heterotrophs > Chemautotrophs > Photoautotrophs (cyanobacteria)
Splitting water*O2 > Aerobes, Ozone layer > Endosymbiosis
Exploring Life’s Origins
The road to all Eukaryotes:
• Endosymbiosis leads to• Membrane bound
• Cellular membranes,
200,000- Homo Sapiens (11:59:30)
Oldest fossils on Earth
Shark Bay, Austrailia 2-3,000yo high salt content 100yrs to grow 5cm living fossils
*Eukaryotes or Prokaryotes?
*Anaerobic or Aerobic?
*Heterotrophs or Autotrophs?
*Marine or CAME
*Why the diversity explosion?
*Warm or Cold Blooded?
Widespread and rapid decrease in the amount
of life on earth.
Sharp change in diversity and abundance.
Species are now
long will it take?
What causes the changes?
evidence do scientists
have to support the Theory of
DNA Sequencing- Universal Code
Fossils are often found in sedimentary rock,
which is formed from layers of silt and sand
covering dead organisms.
Types of Fossils??
In what ways
is the fossil
position (but not
same function) in
“ICA” = Indicates Common Ancestor
Hand, Paw, Fin, Wing??
•Same lineage, evolving
apart to be more different.
•For example, bats and
horses. Both share the
same lineage as mammals,
but the limb of the bat
became wings while the
horse developed hooves.
Similar Appearance and Functiondoes NOT indicate ICA
Ex- Bird and Insect Wings
Porpoise and Shark Fins
Built on a
Organisms having vestigial structures:
ICA with organisms in which the
homologous structure is functional
The closer the DNA sequences of 2 organisms
are, the more closely related they are.
◦ Humans and chimps have DNA that is 98.4% identical
• DNA and RNA are carriers of genetic information
• The genetic code is universal
• Some Metabolic pathways are conserved (same/similar) across all domains
Species change over time, moving toward a
FIRST to clearly state:
Types of organisms changed over time
because of natural phenomenon not divine
New species were modified descendants of
“OUT”/ Discredited Ideas….
Theory of Need: a change in the environment
produced a need for change in organisms
Use and Disuse If organs were used- they
remained, if unused, they would disappear.
“Use it or Lose It”….all inheritable changes
Inheritance of Acquired Characteristics Not
determined by heredity; ‘acquired traits’ are
acquired in ones lifetime in response to ones
experience or behavior.
THEORY OF NATURAL SELECTION
Organisms with traits more
favorable to a particular environment
are more likely to pass on those traits
to their offspring. *Environment plays
a key role.
(HW Ch 18)
WHERE LAMARCK FAILED:
INDIVIDUALS DO NOT EVOLVE, POPULATIONS DO
REV. JOHN HENSLOW
1856 Alfred Wallace
1858 Papers of Darwin &
1859 Publishes his work
VARIATIONS exist in individuals within a species
(caused by mutations/genetic recombination). Those
with favorable variations have an advantage for
Live Longer > Produce more offspring > Genes passed on
OVERPRODUCTION of offspring: More offspring are
produced than can survive, but the population remains
STRUGGLE FOR EXISTENCE: Competition for food,
space, mates (limiting factors).
NATURAL SELECTION –the best adapted are ‘selected’.
Survival of the Fittest = best suited for the
Darwin’s Fittest = Differential Reproductive Success
*HW Ch 18
DESCENT OF MODIFICATION: Similarities in
related species are due to common ancestry
Idea of ‘common descent’ was inspired by
BIOGEOGRAPHY (geographical distribution of
Natural Selection favors Reproductive Success of
certain individuals over others in a population.
Individuals do not evolve, populations do
The study of the past and present geographic
distribution of organisms.
DARWIN: Species found on ocean islands tend
to resemble species of the nearest mainland,
even if the environment is different.
Galapagos (South America)
Cape Verde Island (Africa)
AUSTRALIA: (separate land mass for millions of
years). Has distinctive organisms not found
anywhere else in the world even though climate
is the same.
HHMS-Mice Natural Selection
Review timelines lab assignment and
completed timelines in the classroom
◦ NOTE: 1 Meter stick = 1 Billion Years
4.6 Billion (Age of Earth) = ?
10 cm = ?..........1 cm = ?.........1 mm = 1 million years
CAN ALSO BE DEFINED AS:
change in the frequency of alleles
from one generation to another.
A change in the gene pool of a population
A change in frequencies of alleles in the
gene pool of a population.
Ch 19 -text
• Genes Mutate
• Individuals are selected
• Populations evolve
• LARGE changes, as when new species
• Can SEE the changes
The study of genetic variability within a
population and the evolutionary forces
that act on it.
Distinguishes genetic equilibrium* from
(*relates to the HARDY-WIENBERG
PRINCIPLE; ‘population is at
(Pop. Genetics Handout, slides)
Genetic Drift – due to chance; relates to size of
the population; causes a decrease in variation
within the population; Ex- Bottleneck effect;
Gene Flow – relates to isolation; increases
variation within a population;
Mutation – substitution of alleles
Non-random mating – Ex- Inbreeding (selfpollinating plants); assortive mating (like:like)
Natural Selection – differential success in
reproduction; only cause likely to be adaptive.
*(These are the ANTITHESIS of H-W conditions)
Evolutionary Fitness- The number of
surviving offspring left to produce the next
generation; measure of evolutionary success
Gene flow: random migration
Genetic Shuffling; Non-random* Mating
Variation ~ Differential Reprod. ~ Heredity
Adaptive; Not Random
• Explain the increased frequency of dark moths during the 1880’s in Britain.
• Explain the decreased frequency of dark (melanic) moths from 1960’s to 80’s
• Other ways humans have had an impact on variation in other species (or our own)?
This definition of evolution was developed
largely as a result of independent work in the
early 20th century by Godfrey Hardy, an English
mathematician, and Wilhelm Weinberg, a German
Through mathematical modeling based on
probability, they concluded in 1908 that gene
pool frequencies are inherently stable but that
in all allele
virtually all of the time. They resolved this
do not change
by analyzing theto
mechanisms.of microlarge population
in the absence
genetic drift, etc.)
went from (mutation,
predictions of the probability of specific offspring
genotypes based on parental genotypes to determining
for entire provides:
A means to calculate allelic frequencies
A baseline for comparison
(non-evolving population to an evolving population)
We have a very large population size
Isolation from other populations exists
There are no net mutations
There is random mating; all breed and produce
the same number of offspring
There is no natural selection
HW formula on the AP Equations Handout
p (dom trait) + q (rec) = 1
• (p + q)2 = p2 + 2pq +q2 = 1
• WHERE: In a population….
p = freq of the Dominant allele
q = freq of the Recessive allele
p2 = freq of individual AA
q2 = freq of individual aa
2pq = freq of individual Aa
Diagram of Hardy-Weinberg genotype proportions from male (sperm)
and female (egg) contributions. Given a locus with two alleles
designated A and a that occur with frequencies p and q, the chart
shows the genotype frequencies (p2, 2pq, and q2) as differently colored
areas. Note that the heterozygotes (blue + yellow = green) can be
formed in two different ways.
Albinism is a rare genetically inherited trait that is only expressed in the phenotype of
homozygous recessive individuals (aa). The most characteristic symptom is a marked
deficiency in the skin and hair pigment melanin. This condition can occur among any
human group as well as among other animal species. The average human frequency of
albinism in North America is only about 1 in 20,000.
What have we been given?:
Referring back to the Hardy-Weinberg equation (p² + 2pq + q² = 1), the frequency of
homozygous recessive individuals (aa) in a population is q². Therefore, in North America
the following must be true for albinism:
q² = 1/20,000 = .0005
What can we find out from this information?
By taking the square root of both sides of this equation, we get: (rounded off)
q = .007
In other words, the frequency of the recessive albinism allele (a) is .00707 or ~1 in 140.
With this information, what can we solve for?
Knowing one of the two variables (q) in the Hardy-Weinberg equation, it is easy to solve
for the other (p). P = 1 – q = 1 - .007 = .993
The frequency of the dominant, normal allele (A) is, therefore, .99293 or about 99 in 100.
How can we use this information to determine genotypic frequencies?
98.6% No ‘a’ allele
p² + next
q² =is1to plug the frequencies of p and q
(.993)² + 2 (.993)(.007) + (.007)² = 1
2pq (Aa) = 1.4% carriers
.986 + .014 + .00005 = 1
= .005% Albinos
**Given a Phenotype = p2, q2, 2pq
Allele/Gene Frequency = p,q
REVIEW WORKSHEETProblems 1-8,10 front, 1-6 back
TEXT p415 1,2 (3)
**QUIZ: Day 5
The types of selection relate to the bell curve. The bell curve is altered due
to forces of nature favoring certain traits over other.
(amount of eggs
laid) in starlings is
between 3 and 6.
Clutch size is a
Human Birth Weight: The
optimum birth weight is
the one with the lowest
Galapagos finches- extended drought, wet periods.
The male widowbird collects females for his “harem” by
attracting them by the length of his tail. The longer the
tail, the more females he attracts and mates with.
Rock Pocket Mouse
HHMI- Rock Pocket Mouse 10.25
Male salmon mate at either 2 years old
(Jacks) or 3 yo (hooknoses). Males fight
over who will fertilize the female’s eggs.
The male salmon are either very small or
very large, very few are average size.
Gradual change in genotype and phenotype through a series
of geographically separated populations as a result of an
The creation of a new species. Evolution of
a new species when a population becomes
isolated from other members of the species.
Scientists put every living thing in one of 8
different taxonomic groups:
Beak of the Finch 15.54
REPRODUCTIVE ISOLATING MECHANISMS
Prevention of interbreeding between two different species whose ranges
(habitats) overlap. Most species have two or more mechanisms that block
a chance occurrence of interbreeding between closely related species.
Barriers in place to prevent fertilization/
mating of two different species
1. Temporal isolation
2. Habitat isolation
3. Behavioral Isolation
4. Mechanical Isolation
5. Gametic Isolation
II. POSTZYGOTIC BARRIERS:
Functions after fertilization, prevents
development of viable, fertile offspring
1. Reduced Hybrid Viability
2. Hybrid Sterility
3. Hybrid Breakdown
*Preserve genetic integrity of a
species by preventing gene flow
Two species of
one lives mainly
in water while
the other is
mates in late
skunk mates in
boobies of the
unique to the
These 2 species
of snails have
in their shells so
Gametes of red
and purple sea
the water, but
are unable to
subspecies of the
genus Ensatina can
hybridize, but hybrids
do not complete
development or are
A mule is the
between a male
donkey and a
Hybrids of two
rice strains are
fertile, but the
“Different /native land”
Subpopulation becomes physically separated
from the original population…how?
Land Bridges Develop
*Most Common Method of
speciation, especially in
Sympatric Speciation: “Together/native land”
New species develops in the same geographic
region as the parent population
◦ **Common in Plants
◦ Polyploidy (2 or more chromosome sets)
◦ Allopolyploidy (interspecific hybrid- multiple
sets of chromosomes from 2 or more species)
*Can occur in animals, but how is
TEXT p435, fig 20-9
debated. (Not due to polyploidy)
New species may not compete successfully
with parent species; goes extinct
New species may co-exist with the parent
New species may outcompete parent species;
hybrid may replace the parent(s)
TEXT p436, fig 20-10
Lizards in an evolutionary
Kaibab Squirrels- Gr.Canyon
Common in plants; change
in ploidy (# chromosomes)
and ecology 80% of all
flowering plants- polyploids
Continuous over long
periods of time;
long periods of stasis
interrupted by short*
periods of rapid
be thousands of years)
Large-scale phenotype in populations warrant
their placement in taxonomic groups at the
species level and higher.
Dramatic evolutionary changes that occur over
long time spans.
Dominated by multiple microevolutionary
processes or external, chance events…or both?
Important Aspects of Macroevolution:
1. Appearance of evolutionary novelties
2. Adaptive Radiation
3. Mass Extinction
4. Earth’s Geological History
Ch 20 p439
Huge differences in phenotype leading to different
taxonomic groups. Comes from pre-existing
Jointed appendages, feathers
Originate from modifications of pre-existing
May be due to:
Changes in control/regulatory genes (on/off switch)
Preadaptions (changed from one role/repurposed)
Changes in Allometric Growth “different measure”
Paedomorphosis “child form”
Epigenetics and Gene
Varied rates of
growth for different
retained into the adult
This is an example of
varied changes in
timing of development
Text p 440
of many related
one or a few
species in a
“The Descent of Man”
Darwin, 1871human and apes
shared a common
◦ 3 Domains
◦ 6 Kingdoms
Monkeys, Apes, Humans
Humans & ancestors
to walk upright
Eyes forward- stereoscopic vision/depth perception
Dental formula- same #, type, arrangement of teeth
Long slender limbs/rotate freely at hips/shoulders
5 flexible digits with flattened nails/not claws
Complex social behaviors
Usually 1 offspring at a time; longer parental care
Shape of the Spine, Pelvis
Foramen magnum position
Leg vs arm length
Alignment of great toe
Skull: brain, brow, jaw