2. Outline of Option D
• D.1 Origin of Life on Earth
– Physical conditions
– Miller and Urey’s experiments
– Role of RNA
– Origin of prokaryotes
– Origin of eukaryotes
(endosymbiosis)
• D.2 Origin of Species
– Lamarck and acquired characters
– Darwin-Wallace theory and natural
selection
– Other theories and evidence
• D.3 Evidence for Evolution
– Geographical distribution
– Fossils and dating
– Biochemical evidence
– Homologous structures
• D.4 Human Evolution
– Classification
– Physical features of primates
– Fossil evidence
– Ecological pressures
– Bipedalism and brain size
– Genetic vs. cultural evolution
• D.5 Neo-Darwinism
– Mutations and examples
– Recombination
– Adaptations
– Speciation and isolation
– Gradualism
– Punctuated equilibrium
• D.6 The Hardy-Weinberg Principle
– Calculation of allele, genotype, and
phenotype frequencies
– Conditions of HW equilibrium
4. D.1.1 Outline the conditions of pre-biotic Earth, including high
temperature, lightning, UV light penetration and a reducing atmosphere
• The Earth formed about 4.6 bya
– Collisions of material (comets and meteorites) led
to the formation of the planet
– As the mass increased, gravity and radioactive
decay caused the formation of the dense metal
core surrounded by the liquid mantle and topped
with the solid crust
– Cooling of the crust led to the formation of a very
hot, dense, reducing atmosphere
• “Pre-biotic” Earth
– Reducing atmosphere
• No oxygen (O2)
• Reducing (hydrogen-containing) agents
present
– hydrogen, water vapor, methane, ammonia,
nitrogen, and hydrogen sulfide
– High temperatures
– High UV light levels
– Frequent lightning storms
5.
6. D.1.2 Outline the experiments of
Miller and Urey into the origin of
organic compounds.
• Miller and Urey (1953)
– Simulated conditions of early
Earth in order to determine
whether chemical evolution
could occur in “primeval soup”
– Sealed water, methane,
ammonia, and hydrogen in
sterile glass flasks connected by
tubing
– One flask contained water and
another contained a set of
electrodes
– The water was heated to
produce vapor and sparks were
produced with the electrodes to
simulate lightning
– The mixture was allowed to cool
and condense and drip back into
the first flask to simulate
processes likely to have
occurred on Earth
– This continued for one week,
then M & U analyzed the
contents to find:
• 13 amino acids present (of the
20 that occur naturally)
• High concentration of adenine
7. D.1.3 Discuss the hypothesis that the first
catalysts responsible for polymerization
reactions were clay minerals and RNA
• Miller and Urey’s experiments provide a hypothesis for the origin of
amino acids and nucleotides
– Subsequent experiments produced all 20 amino acids, nucleic acids,
sugars, lipids, and nucleoside triphosphates from inorganic compounds
How did the compounds combine to form larger polymers?
• RNA can act as both a form of genetic material and an enzyme
– Rybozymes are short sequences of RNA that can act as enzymes and
are capable of
• Polymerizing nucleotides using ATP (and are thus capable of replication)
• Cleaving chemical bonds, including peptide bonds
– Ribosomes (composed of rRNA) are rybozymes
• Clay minerals
– RNA and other organic compounds adhered to clay particles
– Clay exists in very close layers, concentrating amino acids and other
monomers in a small area
– Metal ions in the clay may have acted as catalysts for dehydration
reactions
– Clays provide stable environments for polymerization
D.1.4 Discuss the possible role
of RNA as the first molecule
capable of replicating
8. D.1.5 Discuss a possible origin of membranes and prokaryotic cells
Origin of Membranes
• All cells are surrounded by
membranes, and formation of
these was critical in the
development of the first cells
• Closed membrane vesicles
can form spontaneously from
lipids
– Due to structure and
hydrophobic properties (think
about a phospholipid)
• The first prokaryotes required
a genetic mechanism and a
membrane enclosure
Origin of Prokaryotic Cells
• Coacervates are like little
bundles of organic material
surrounded by a hydrophobic
layer
• Protobionts are groups of
abiotically produced molecules
– Probably preceded by
coacervates
– Surrounded by a protein
membrane (can form bilayer in
the presence of lipids)
– Maintain fairly constant
internal environment
– Probably the predecessors for
the first prokaryotes
– With RNA, these molecules
could replicate and pass on
their characteristics
9. D.1.6 Discuss the endosymbiotic theory for the origin of eukaryotes
• Anaerobic prokaryotes eventually developed chlorophyll and a
simple form of photosynthesis, leading to the accumulation of
oxygen in the atmosphere and aerobic life
• Review—differences between prokaryotes and eukaryotes?
• Endosymbiotic theory: chloroplasts and mitochondria are derived
from free-living prokaryotes that were engulfed by larger
prokaryotes but survived inside the cytoplasm
– Mitochondria probably evolved from proteobacteria
– Chloroplasts probably evolved from cyanobacteria
• Evidence for endosymbiotic theory
– Both mitochondria and chloroplasts contain DNA that is different from
nuclear DNA and similar to bacterial DNA
– Both are surrounded by double-membranes similar to prokaryotic
membranes
– New organelles are formed by a process similar to binary fission
– Internal structure of chloroplasts similar to structure of cyanobacteria
– Analysis of nuclear DNA in plants suggests that some genes were
incorporated from DNA of the chloroplast
– Ribosomes are found within mitochondria and chloroplasts and
resemble bacterial ribosomes
12. D.2.1 Outline Lamarck’s theory of evolution by the inheritance of acquired characteristics
D.2.2 Discuss the mechanism of, and lack of evidence for, the inheritance of acquired
characteristics
• Lamarck (1809) proposed a theory
based on the inheritance of acquired
characteristics
• Acquired characters are those that are
acquired during an organism’s lifetime
– For example, if muscles are used, they
grow stronger
• Giraffe example: The ancestors of
modern giraffes had short necks.
According to Lamark’s theory, the
giraffes had to stretch up to the trees to
reach their food, so their necks
lengthened slightly. The next generation
inherited the lengthened necks and
stretched more. After many generations,
long-necked giraffes came into existence.
• No significant cases of acquired
characters have been found, and
Lamarck’s theory does not fit in with the
principles of inheritance—no mechanism
exists for the acquired character to cause
a mutation in the gene controlling the trait
13. D.2.3 Explain the Darwin-Wallace theory of evolution by natural selection
• Darwin and Wallace proposed the theory
of evolution by natural selection in 1858
– Evolution is the accumulation of changes in
the heritable characteristics of a population
– A series of observations and deductions led
to the development of this theory
Observation Deduction
Populations tend to increase
exponentially, but the number of
individuals in a population remains
nearly constant
More offspring are produced than the environment can
support; there is a “struggle for existence” in which
some individuals survive and others die
Living organisms vary; some
individuals have characteristics that
make them better adapted to their
environment than others
The better-adapted individuals tend to survive and
reproduce more than less well-adapted individuals (this
is natural selection)
Much variation is heritable Better-adapted individuals pass on their characteristics
to more offspring than less well-adapted individuals,
causing the results of natural selection to accumulate.
Over generations, the characteristics of the species
gradually change (this is evolution)
14. D.2.4 Discuss other theories for the origin of species including special creation and panspermia
D.2.5 Discuss the evidence for all these theories and the applicability of the scientific method for
further investigation
• Other theories for the origin of
species exist…
– Spontaneous Generation
• Life arises from non-life
• Pasteur’s experiments disproved
theory
– Special creation
• God created life
– Panspermia
• Organic material arrived on
Earth from space
• This theory has not been
scientifically excluded
– In a 2001 study, experiments
simulated interstellar dust
clouds containing ammonia,
CO2, and methanol mixed with
ice crystals at low temperatures
and high levels of UV
– Organic compounds were
formed
• The scientific method cannot
be used to test these
– Modern experiments will never
determine with certainty what
happened billions of years ago
– Experiments (such as Miller &
Urey’s) determine what is
possible in conditions known
to have existed
16. Types of Evidence
There are three basic types of evidence for a common ancestor:
• Geographic
– Similar organisms exist in areas of the world known to have been
connected by land at some point in the Earth’s history
• Biochemical
– Comparisons of DNA and amino acid sequences reveal similarities
among all organisms
• Paleontological
– The fossil record provides information about organisms that lived in the
past—some of which are similar to modern organisms
When all available evidence is compiled, phylogenies can be
constructed.
17. D.3.1 Describe the evidence
for evolution as shown by the
geographical distribution of
living organisms, including the
distribution of placental,
marsupial and monotreme
mammals.
18. Evolution of monotremes, marsupials, and placental mammals
• The groups of mammals
– Monotremes
• Egg-laying mammals
• Examples: platypus and some
anteaters
– Marsupials
• Young carried in “pouch” until fully
developed
• Examples: kangaroo, koala
– Placental mammals
• Young carried in uterus until fully
developed and nourished by placenta
• Examples: humans, dogs, horses
• Looking at the way in which continents have
drifted over time and examining the fossils
in them we can map out the development of
different sorts of mammals
– Monotremes and marsupials developed in
Gondwanaland (about 165mya)
• Native mammals in Australia are
monotremes and marsupials (due to
geographical isolation)
– Placental mammals developed later (about
135mya) and replaced almost all of the
monotremes and marsupials in the other
continents
– Mammal groups were geographically
isolated and evolved independently
– Similar organisms evolved to fit similar
niches on different continents
19. • Asia and North America are only
separated by a small, shallow sea—the
Bering Straight
• The sea level has risen and fallen
several times through the Earth’s
history, allowing several periods of
exposure of a “land bridge” between the
continents
– About 1,000 miles long at longest point
– Allowed land mammals to pass
– Believed to have enabled human
migration to the Americas from Asia
about 25,000 years ago (some
disagreement on time frame)
• Both continents have similar mammal
life
– Ancestors of cows, sheep, horses, rhinos
and other mammals may have evolved in
Asia and migrated to North America
– Migration from North America to Asia
likely occurred as well—horses and
camels originated in N.A. and spread to
S.A. and Asia
Role of the Bering Land Bridge
20. D.3.2 Outline how remains of past living organisms have been preserved
• Fossils are the preserved remains
of an organism
• The remains of organisms can be
preserved in many ways…
– They may be trapped in resins
(sap) which become amber
– They may be frozen
– They may be trapped in acid peat
(partially decomposed organic
material), which prevents decay
– The may be trapped in sediments
that become rock
Ancient
bird skull
preserved
in peat
Scallop fossils preserved in sediment
Insect
preserved
in amber
21. D.3.4 Define half-life and D.3.5 Deduce the approximate age of
materials based on a simple decay curve for a radioisotope
• Half-life: the time for half of
the radioactive atoms in a
sample to undergo decay
– Radioactive decay takes
place at a constant rate
independent of physical
conditions
– Decay depends only on time!
Questions:
1. After three half-lives, what fraction of the
original radioactive isotope remains in a
sample?
2. A piece of fossilized wood has a carbon14
radioactivity that is 1/4 that of new wood.
The half-life of carbon14 is 5730 years.
How old is the fossilized wood?
22. D.3.3 Outline the method for dating rocks and fossils using
radioisotopes, with reference to 14
C and 40
K
• Radioisotopes are radioactive isotopes of chemical elements
– Isotopes of an element have the same number of protons but differing numbers
of neutrons, giving them different masses
• The amount of a radioisotope in a preserved sample can be measured and,
the decay curve of the isotope can be used to determine the age of the
sample
• 14
C and 40
K are commonly used in dating
– Radiocarbon dating using 14
C
• The percentage of surviving 14
C atoms in a sample is measured
• The half-life of 14
C is 5730 years, so it is most useful in dating fossils between 1000 and
100,000 years of age
• Can be used to date organic material produced by living organisms; as long as the
organism is living, it contains the same proportion of 14
C as the atmosphere. When it
dies, the 14
C begins to decay into 14
N
– Potassium-argon dating using 40
K
• 40
K decays into 40
Ar over time
• The proportions of both are measured
• The half-life of 40
K is 1250 million years, so it is useful in dating samples older than
100,000 years
• Can be used to date rocks and mineral-containing samples
23. D.3.6 Outline the paleontological evidence for evolution using one example
• Paleontological evidence for
evolution is provided in the fossil
record
– The fossil record is the sum total of
fossils discovered to date
– Fossils are organized based on age
and the similarities of structures
– It is incomplete—why?
Example of paleontological evidence:
• Acanthostega may be a “missing
link” between terrestrial and aquatic
organisms
• Characteristics:
– Eight digits on each “hand” and “foot”
linked by webbing
– Lungs as well as gills
– Limbs not particularly well-adapted to
bearing weight
– Primarily aquatic
24. D.3.7 Explain the biochemical evidence provided by the universality of DNA
and protein structures for the common ancestry of living organisms
• Remember the idea of the “Universal Genetic Code”… all
organisms utilize the standard genetic code
– All have DNA
– DNA is transcribed into RNA
– RNA is translated into chains of amino acids based on the
genetic code…
• Exceptions:
– Small deviations from the code in the protein synthesis of yeast
and some protozoans
• It is thought that since all organisms have a VERY similar (if
not identical) code, then the genetic code was present in the
first common ancestor
• Analysis of biomolecules including proteins provides further
evidence for common descent
– The protein cytochrome c is an electron carrier that is required
for aerobic respiration
– It is a complex molecule found in plants, animals, unicellular
aerobes
– Provides strong evidence that all aerobic organisms descended
from a common ancestor—it is very unlikely that unrelated
organisms would have independently evolved the ability to
produce this complex enzyme
25. D.3.8 Explain how variations in specific molecules can indicate phylogeny
• Researchers have the capability of determining the
sequence of amino acids in a protein or nucleotides in a
molecule of DNA
• Comparisons of these sequences can be made between
organisms to determine how closely they are related
– Remember the amino acid comparison of primates we did last
year?
– Humans and chimpanzees have identical amino acid sequences
in both alpha and beta hemoglobin
– Orangutans differ from humans in two amino acids
– Humans are more closely related to _______ than _______
26. β hemoglobin comparison
The number of “changes”
is the number of
differences in the amino
acid sequence of the
protein between the
divergent groups.
27. D.3.9 Discuss how biochemical
variations can be used as an
evolutionary clock
• The more closely related the
species, the fewer variations in
amino acid or DNA sequence,
and the shorter period of time
since divergence
• More distant relatives have
more variations and diverged
earlier
• The idea of an evolutionary
clock allows us to organize the
species based on when
divergence occurred
– Assumptions:
• The rate of change of any
protein or DNA sequence is
approximately constant over
time
• The rate of DNA replication is
constant over time and across
all species
– So, there is some uncertainty,
but the approximate time since
divergence can be determined
based on the number of
differences in a DNA sequence
Evolutionary Clock
28. D.3.10 Explain the evidence for evolution provided by homologous anatomical
structures, including vertebrate embryos and the pentadactyl limb
• Homologous character: a structural or
biochemical trait which is shared between
two or more organisms because of a
common ancestor
– Examples:
• vertebral columns in vertebrates
• pentadactyl limbs
• vertebrate embryos
29. Pentadactyl (5-digit) Limbs
X
• Nearly all vertebrates have a pentadactyl limb
• Structure is similar in all, despite different uses for the limb
31. D.3.11 Outline two modern examples of observed evolution. One example must
be the changes to the size and shape of the beaks of Galapagos finches.
Galapagos Finches
• The 1977 drought in the
Galapagos led to a 4% increase in
beak size of finch species
Geospiza fortis—afterwards the
average beak was short and wide;
the diet consisted of large, hard
seeds
• El Niño event in 1982-3 caused an
increase in precipitation and
changed the vegetation—fruits
became smaller and softer
• Finch population grew
exponentially due to rains and
increase in food, then fell
• By 1987 average beak was longer
and narrower than pre-1982
Ladybugs
• The majority of ladybugs in
industrial (high smog) areas of
Europe in 1960 had a black
phenotype
– black absorbs more light, and so
the black bugs have an advantage
staying warm when sunlight levels
are low
• After 1960 as smog levels
decreased the proportion of black
ladybugs decreased proportionally
• By 1980, both smog and black
butterflies reached constant low
level
• Post-1980, the majority of
ladybugs were red
– red coloring warns predators that
they are poisonous and is more
effective at improving survival
when light levels are normal
33. D.4.1 State the full
classification of human beings
from kingdom to sub-species
Kingdom Animalia
Phylum Chordata
Class Mammalia
Order Primate
Family Hominidae
Genus Homo
Species sapiens
Subspecies sapiens
34. D.4.2 Describe the major
physical features, such
as adaptations for tree
life, that define humans
as primates
Characteristics of all members of the Primate order:
• Hands and feet
– Able to grasp, with long fingers and an opposable
thumb
– Sensitive fingers
• Limbs
– Highly mobile arms and hands (able to rotate)
• Vision
– Stereoscopic = able to see objects in 3 dimensions
– Forward-facing eyes on flattened face, giving
overlapping fields of view
– Enhanced depth-perception and hand-eye
coordination
• Olfaction
– Reduced sense of smell, allowing flatter face
• Skull
– Enlarged and expanded for cerebrum (site of
perception, imagination, thought, judgment, decision)
– Modified for upright posture
• Brain
– Increased sensory/motor areas
• Few offspring
• Social dependency
Arboreal
Adaptations
35. D.4.3 Discuss the anatomical and biochemical
evidence which suggests that humans are a
bipedal and neotenous species of African ape
that spread to colonize new areas
• Humans and apes…
– care for their young for a long time
– have delayed puberty
– have dexterous hands and similar
hips and muscles
• We may be neotenous – evolved
to retain juvenile ape
characteristics
– Humans show more physical
similarities with young apes than
mature ones
• 98% of human and chimpanzee
DNA is exactly the same
• Fossils have been found of
intermediate species in the
evolution of humans from apes.
36. D.4.4 Outline the trends illustrated by the fossils of
Australopithecus and Homo
• See chart
• Over time, trends show…
– Increasing skull size with respect to body mass
– Increasing brain capacity
– Posture becoming more erect
• Increasing degree of bipedalism
• Decreased size of neck muscle
• Forward movement of foramen magnum (site in the skull
through which the spinal cord passes)
– Jaw becoming more V-shaped and less U-shaped
• Canines and molars reduced in size due to changes in diet
– Increasing ability to grasp with hands
37. D.4.5 Discuss the possible ecology of these species and the ecological
changes that may have prompted their origin
• Climate changes:
– Eastern Africa became drier
with thin woodlands instead of
forests (about 5 mya)
• Led to evolution of bipedal
ground-adapted species that
could move on land for long
distances and gather scattered
food
– Later (about 2.5 mya) Africa
became much cooler and
drier
• Mostly savanna and grasslands
• May have prompted the
evolution of the Homo genus
which used tools and group
work to hunt large animals for
food
38. D.4.6 Discuss the incompleteness of
the fossil record and the resulting
uncertainties with respect to human
evolution
• As previously discussed, the
fossil record provides one type of
evidence for change over time
• Criticisms of using fossils in
support of evolution include the
lack of continuous record, many
gaps or “missing links”
• Possible explanations for
incompleteness of fossil record:
– Punctuated equilibrium
• Intermediate organisms would
exist in few numbers, making
fossilization less likely
– Decomposition or consumption
of dead organisms by
scavengers
– Relatively rare fossilization of
soft-bodied organisms
– Relatively rare conditions
favorable for fossilization
– Fossilized organisms
infrequently unearthed
39. D.4.7 Discuss the origin and consequences of bipedalism and increase in brain size
• Increased brain size
– Greater ability to adapt to different
environmental circumstances
• Tool-making
• Construction of shelters
• Use of fire
– Transmission of cultural behaviors
between generations
– Longer gestation and care of young
after birth during period of brain
development
• Critical period from birth to two years
• Bipedalism
– Led to shorter arms, longer and
stronger legs
– Knee allows leg to fully straighten
– Rigid foot with shorter, non-opposable
toes
40. D.4.8 Outline the difference between genetic and cultural evolution
D.4.9 Discuss the relative importance of genetic and cultural evolution
in the evolution of humans
• Genetic evolution
– Genetic changes that have occurred during
hominid evolution; differences observed between
individuals of different racial or cultural groups
• Cultural evolution
– Changes in the actions and ideas of society,
including transmission of these from one
generation to the next
– Typically involves writings, spoken word, and
images
• Unique to human societies!
• Hominization: “becoming human”
– Involved concurrent physical and social changes
• Example: changes in sexual behavior (due to
physical changes) led to formation of monogamous
pairs which lived together with their children; led to
formation of communities which shared food and
resources
