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I. Early Earth and the origin of life
A. Origin of the Universe (15 BYA)
1. Many theories exist
2. Most scientists favor the Big Bang
Theory which state that the universe
began as a dense concentration of matter
smaller than a speck of dust which
exploded outward violently
Great Explanations of The Big Bang
Theory appear in these books:
B. Origin of the Sun (10 BYA)
1. Clouds of molecules, made of hydrogen gas, began to
grow in mass which increased their gravity, which in
turn, attracted more hydrogen to increase their mass
2. These clouds increased to such a huge mass, that it’s
gravity smashed hydrogen molecules together,
triggering a Fusion Reaction. We call these fusion
reactions clouds Stars and one formed our Sun
Relative Size of Inner Planets
Relative Size Outer Planets
Size of Planet Relative to the Sun
Size of Sun Relative to Other Stars
Our Sun Relative to the Largest Stars
C. Origin of Earth
1. Clouds of matter caught
in the Sun’s
gravitational field began
forming Planets
2. Solid matter collected
into a dense core and
radioactive decay melted
the matter into a ball of
molten rock that we call
Earth
Earth at Birth (4.5 BYA)
3. Conditions of Early Earth
Prevented Life
a)
b)
c)
d)
e)
Tidal waves of Lava
Poison gas atmosphere
Deadly ultraviolet rays
Constant meteorite bombardment
Frequent earthquakes
D. The Antiquity of Life
1. Life Appeared relatively early in Earth’s history
a) Fossils of prokaryotes have been recovered from
stromatolites that are 3.5 billion years old
b) The oldest eukaryotes are 1.5 billion years old
2. Multicelled organisms arose 700 million years
ago
E. Spontaneous generation of Life: Abiogenesis
1. Abiogenesis is NOT evolution
2. Russian Biochemist Alexander Oparin introduced a
plausible theory of chemical development of life in 1927
F. Origin of Life: Oparin/ Haldane Model
1. Abiotic synthesis and accumulation of small
organic molecules: Amino Acids, Nucleotides and
Sugars
2. The joining of monomers to form polymers
3. The formation of protobionts- groups of
abiotically produced molecules able to maintain an
internal environment
4. Origin of heritable Material
A) DNARNAprotein model most likely evolved from a
simpler model
B) One hypothesis proposes RNA to be the first genetic material
C) DNA was later favored due to its stability
G. Evidence to Support the
Oparin/Haldane Model
1.
2.
Stanley Miller & Harold
Urey constructed a
primitive earth machine
with methane, Ammonia,
water vapor and hydrogen
in the atmosphere which
produced organic molecules
Various experiments have
produced all 20 amino
acids, ATP, sugars, and
DNA and RNA bases
3. Sidney Fox produced proteinoids:
abiotically produced polypeptides
a) Clay, hot sand and
rocks can contain
metals which will
catalyze condensation
reactions .
b) Pyrite can provide a
charged surface or free
electrons to support
bonding between
molecules
4. When mixed with cool water, proteinoids self-assemble into
Microspheres surrounded by a selectively permeable
membrane
5. Coacervates form spontaneously from drops of
polypeptides, nucleic acids and polysaccharides
6. RNA can base pair in the presence of zinc
7. RNA is autocatalytic- it can catalyze the formation of mRNA,
tRNA, and r-RNA by itself
8. RNA fold is determined by its sequence
a) This provides a mechanism for natural selection
b) Stability and catalytic activity would be favored
What does DNA and RNA polynucleotides with
protein catalyzing chemical reaction in a lipid
membrane sound like?
A cell of course!
But, scientists have only produced Coacervates in the lab
DNA replication requires enzymes and DNA is
required to make enzymes.
Therefore, current theory suggests that the first genetic
material was RNA because it can be auto catalytic
(RNA could catalyze its own replication.)
But, replication produces a complementary strand, not a
coding strand, so two replications would be required.
E. Origin of Eukaryotes
1. Autogenous Model- eukaryotes evolved by
specialization of internal membranes
derived from the prokaryotic plasma
membrane
a) Most endomembrane structures are
believed to have differentiated from the
plasma membrane invaginations
b) Double membrane organelles
(chloroplasts & mitochondria) may have
involved secondary invaginations or more
complex folding
2. Endosymbiotic Model- certain prokaryotic
species called endosymbionts lived within
prokaryotes
a) Focuses mainly on chloroplasts and
mitochondria
b) Chloroplasts are thought to have descended
from endosymbiotic photosynthesizing
prokaryotes living in larger cells
c) Mitochondria are postulated to be descendants
of prokaryotic aerobic heterotrophs that may
have been parasites or undigested prey of larger
cells
3. Evidence for the Endosymbiont model
a) Appropriate size to be descendants of
eubacteria
b) Replicate by splitting as do prokaryotes
c) Contain their own DNA and ribosomes
similar to prokaryotes
d) Replicate independent of the cell
II. Evidence of Evolution
A. Fossil- any
preserved
remnants or
impression left by
an organism that
lived in the past
1. Fossil Formation
a) Some fossils are found as thin films pressed
between layers of sandstone and shale and retain
organic material
b) Most fossils form from the mineral rich hard
parts (bone, teeth, shells) because other
substances decay rapidly
c) Other fossils found by paleontologists are
replicas, casts or molds left when corpses where
covered by sand or mud
2. Limitation of the Fossil Record
(Fossilization requires a series of improbable events)
a) The organism must die at the right time in
the right place in an anaerobic
environment to avoid decaying
b) Geological events must form the fossil and
then the fossil must escape geological
events such as erosion, pressure and heat
c) Finally, the fossil must be found by
someone who knows what they are doing
3. Ramifications of Fossilization:
a) Most species never leave fossils
b) Most formed fossils have probably been
destroyed
c) Only a small number of existing fossils
have been found
d) Therefore, the fossil record is composed
of organisms that were widespread,
abundant, lived a long time and had hard
shells or skeletons
4. Fossil Dating
a) Relative Dating
1) Younger strata is deposited on top of older
2) Strata from different sites can be correlated by similar
fossils known as index fossils
3) Geologist have formulated a sequence of geologic
periods by comparing many different sites
b) Absolute Dating: Not errorless. +/- 10%
1) Radiocarbon Dating: uses C14 which has a half-life
of 5730 years. Useful for dating organic matter less
than 50,000 years old
2) K40 has a half life of 1.3 billion years old
3) Living organisms synthesize L-form amino acids
which decay to D-form over time
B. Biogeography- the geographical
distribution of species
1. Islands with similar environments in different
parts of the world are not populated by closely
related species, but rather species related to
organisms form the nearest main land
2. South American tropical mammals are more
closely related to South American dessert
animals than to African tropical animals
3. Australia has a diversity of marsupials in an
environment that could easily support placentals
C. Taxonomy- reflects the branching
genealogy of the tree of life
1. Different taxonomic levels are related
through descent from a common ancestor
2. Organisms thought to be closely related on
the basis of anatomical features reveal
common hereditary background
D. Comparative Anatomy- Anatomical similarities
between groups of the same taxonomic category
show evidence of common descent
1. Forelimbs of mammals are Homologous
Structures- structures that are similar due to
descent from a common ancestor
a) Although the limbs re used for different functions, it
is obvious that the same skeletal elements are present
b) It is logical then that the foreleg, wing, flipper or arm
are similar due to a common ancestor
2. Vestigal Organs- rudimentary organs of little or
no use to an organism that were valuable to the
ancestral form. I.e. hip bones in snakes
Homologous Bone
Structures
Similar structures
found in different
organisms suggests
a common ancestry
E. Comparative Embryology
Closely related
organisms go
through similar
stages in their
embryonic
development
1. All vertebrates (Fishes, Amphibians, reptiles, birds and
mammals) go through an embryonic stage in which they
posses gill slits on the sides of their throats
a) As development progresses, gill slits develop into
divergent structures, In humans, they form the
Eustachian tubes that connect the middle ear and
throat.
b) Supports conclusion that all vertebrates descended from a
common aquatic ancestor
2. Comparative embryology can often establish homology
among structures that are so altered later in development
that their common origins cant be determined by their fully
developed forms
F. Molecular Biology Organisms with
similar proteins and DNA have similar ancestors
1. The closer two species
are taxonomically, the
higher the percentage of
DNA they share
2. Even taxonomically distant
organisms share some DNA
and protein. This
substantiates the idea that all
life forms are related to some
extent
Examine the following DNA sequences. Which two
of the three organisms is most closely related?
Organism A: GGT CTC AAT GTA ATC CAA TCC AGG
Organism B: GGT CAC ATT GTA ATG CAA TCG AGG
Organism C: GGA CTC ATT GTA ATC CGG TCC AGC
A & B Matches: 20 A & C Matches: 19 B & C Matches: 17
A & B are most closely related
III. Mechanisms of Evolution
Charles Darwin
A. Natural Selection: Charles Darwin
1. All species have such a great potential fertility
that their population size would increase
exponentially if all individuals born would
reproduce successfully
2. Most populations remain stable except for
seasonal fluctuations
3. Natural Resources are limited
a) Production of more individuals than the environment
can hold leads to a struggle for resources
b) Only a fraction of the original offspring survive
4. Individuals of a population vary extensively in
character
5. Variation is due to random fertilization,
independent assortment, crossing over, and
mutation
a) Survival is not random, but depends on the
genes of the individual
b) Organisms with favorable genes will live
longer and have more offspring than those
with average or poor genes
c) Favorable genes will accumulate over
generations
B. Population Genetics
1. Individuals do not evolve.
Therefore, populations must be
studied.
2. Population- a group of
interbreeding individuals of the
same species that share a
common geographic area
3. Gene Pool- total aggregate of
all the genes in a population at
any one time. Let’s fiddle
around with some gene and
genotypic frequencies
Gene Pool
4. Hardy-Weinburg Theorem- Equations used to
calculate gene and genotypic frequencies at genetic
equilibrium. I.e. No evolution is occuring
a) Gene Frequencies
1) Let P = the frequency of Dominant Genes in a population
2) Let q = the frequency of Recessive genes in a population
3) Therefore:
P+q=1
All the dominant genes + all the recessive genes = all the genes
b) Genotype Frequencies
Hardy-Weinburg Notation
1) PP or P2
2) Pq + qP or 2Pq
3) qq or q2
Therefore:
Genotypes
Homozygous Dominant p
Heterozygous
q
Homozygous Recessive
p
q
P2
Pq
qP
q2
P2 + 2Pq + q2 =1
All the Homozygous Dominant + All the Heterozygotes + All the
Homozyous Recessives = All the Population
With these formulas, you can solve all Hardy-Weinburg problems
c) Hardy-Weinburg Equilibrium will be
maintained if the following conditions are met:
1)
2)
3)
4)
5)
Infinitely large population size. This eliminates gene
frequency change due to chance called Genetic Drift
No immigration or emigration. Organisms entering or
leaving the population changing gene frequencies called
Gene Flow
No differential rates of mutation. The rate at which A
mutates to a is equal to the rate at which a mutates to A
No mating preferences. The chances of any one
genotype mating with another geneotype is equivalent to
its frequency within the population
No selection. All genes are neutral with each one having
the same survival value
C. Causes of Microevolution- the
change in gene frequencies within
a population
1. Genetic Drift- change in gene frequency due to
random chance
2. Bottle Neck Effect- following a natural disaster,
the small remaining population is unlikely to
represent the genetic make up of the original
population
3. Founders Effect- genetic drift that occurs when
a few individuals colonize a new habitat
Causes of Microevolution
4. Gene Flow-immigration or emigration of
individuals disproportionately
5. Mutation- introduces new alleles into the
population and immediately changes the
gene pool
6. Non-Random Mating
a) Individuals selecting mates that are
geographically neighbors can lead to
inbreeding
b) Assortive Mating- individuals having a
mating preference.
7. Natural Selection- a given phenotype is
selected for (increasing gene frequency) or
against (decreasing gene frequency)
Ex. H. B. Kettlewell’s Experiment with the
selection of moths by bird predators
In England, before the industrial revolution, tree bark was a lighter
color and lighter moths out numbered darker moths 9:1
Coal caused the tree bark to darken during the industrial revolution. The
darker moths then numbered the lighter moths 9:1
Geospiza
fortis
Study by Peter and Rosemary Grant
Antibiotic Resistant Strains of Bacteria are
a Prime Example of Evolution
IV. Speciation-
The Development of New Species
A. Types of Speciation
1. Anagenesis- the transformation of an unbranched
linage enough to justify renaming it as a new species
2. Cladogenesis- the branching of one species into two
or more species
B. What is a Species?
1. Morphospecies- a species defined by
anatomical feature
2. Biological Species- a group of individuals
that can successfully interbreed and
produce fertile offspring
C.
Reproductive Barriers Produce New Species
1. Prezygotic Barriers- prevent zygotes from forming
a) Habitat Isolation- two species having different
habitats in the same area
b) Temporal Isolation- two species bread at
different times of the day, season, or year
c) Behavioral Isolation- two species don’t
recognize the others behavior used to attract a
mate
d) Mechanical Isolation- anatomical
incompatibility may prevent sperm transfer
when closely related species attempt to mate
e) Gametic Isolation- sperm from one species
cannot fuse with the egg of another species
2. Post Zygotic Barriers- prevent the production
of a viable, fertile offspring
a) Hybrid Inviability- zygote fails to develop or
an extremely frail offspring dies soon after birth
b) Hybrid Sterility- hybrids are viable but sterile
due to different number of structure of
chromosomes
c) Hybrid Breakdown- First generation is viable
and fertile, but successive generations are feeble
or sterile
3. Introgression- the transplantation of alleles
between the gene pools of different species
D. Biogeography of Speciation
1. Allopatric Speciation- occurs
when a splinter population
diverges in evolution from ist
parent population after becoming
geographically isolated
a) Small populations are the best
candidates because genetic drift and
isolation can rapidly change a small
gene pool
b) Adaptive radiation- the emergence
of numerous species from a common
ancestor can be easily seen or island
chains
2. Sympatric Speciation- New species forming
without geographic isolation due to
reproductive isolation
a) Autopolyploid- a species arises when it
doubles its previous chromosome number
due to failure in meiosis
b) Allopolyploid- a polyploid hybrid is
formed from the contributions of two
different species
E. Genetic Mechanisms of Speciation
1. Speciation by divergence
a) Two populations adapt to different
environments and accumulate differences in
genotype and phenotype
b) Sexual Selection- can lead to reproductive
barriers. According to the recognition
concept of species, Natural selection would
amplify adaptations that would enhance
reproductive success
1) The adaptations may cause recognition problems
2) This can result in speciation
.
2. Speciation by Peak Shifts
a) Each adaptive peak is an equilibrium in
which allelic frequencies maximize the
average fitness of the populations members
b) Environmental change may redefine the
landscape, making new adaptive peaks
possible
c) Non adaptive shifts may destabilize a gene
pool through genetic drift, bottle neck or
founders effect and result in a new adaptive
peak
F. Gradual and Punctuated Speciation
1. Gradual speciation- occurs over a long
period of time by the accumulation of
microevolutionary change in the gene pool
2. Punctuated Speciation – new species
arise quickly following its budding from
its ancestral species and then stabilizes for
a relatively long time
V. Macroevolution- the origin
of taxonomic groups higher than
the species level. Macroevolution
is concerned with major events in
the history of life and the origin of
new designs
A. The Origin of Evolutionary
Novelties
1. Preadaptations- a structure that evolved
in one context and became co-opted for
another function
2. Development and Macroevolution
a) Changes in the rate or pattern of development
can be due to small changes in regulatory
genes, but can result in great morphological
differences. I.e. Allometric growith
b) Genetic changes that alter the timing of development
may prevent structures from developing. Paedomorphosis
is a condition where juvenile structures are found in the
adult
B. Difficulties in Interpreting
Evolutionary Trends
1. A single correct evolutionary progression
cannot be produced by the fossil record.
I.e. Evolution of a horse
2. Evolution has produced many trends even
if some branches go against the trends
3. Evolutionary trends may cease or reverse
with changing conditions
C. Continental Drift and
Biogeography
1. Macroevolution has a dimension in space as well
as time
2. Continental Drift has had a significant impact
on the history of life by causing major
geographic rearrangements affecting
biogeography and evolution
3. The formation of the super continent Pangea
and its subsequent break up can explain many
cases of geographic distribution today
D. Punctuations in the History of Biological Diversity
1. Major Adaptive Radiations
a) Evolution of novel characteristics can open the way
to new adaptive zones allowing many taxa to
greatly diversify
1) A large increase in the diversity of sea animals occurred
between the precambrian and paleozoic era
2) This occurred because bones and shells were developed
allowing many groups to diversify greatly
b) Empty adaptive zones can be exploited if the
appropriate evolutionary novelties arise
1) Mammals existed for 75 million years before the first
large adaptive radiation
2) Early in the cenozoic, mammals radiated out due to the
ecological void created by the extinction of the dinosaurs
2. Mass Extinctions
a) About 12 have occurred
b) Mass extinctions profoundly effect the
biodiversity by elimination of many
species. But also allows other species to
radiate out