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Evolution
Darwin, Variation, and History of
Life
Why Do We Study Evolution?
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Evolution is a major part of modern science.
The debate is NOT whether evolution happens
or not…it does!
 Rather, the debate is with the Origin of all
Species on Earth ( a totally different thing).
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Creationism, Intelligent Design, Natural Selection?
When was the Earth created?
Did all living things evolve from one (1) ancestor?
Evolution
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Evolution: Change Over Time
Charles Darwin made a voyage on the HMS
Beagle in 1831 as the ship’s naturalist.
On this voyage, he collected many unique
specimens that he had never seen and were
not documented.
Darwin noted the diversity of organisms, how
well-suited each organism was to its
environment, and new fossils (remains of
living things) that were either similar to
existing organisms or very unique.
Darwin’s Influences
Hutton (1785) – proposed that
Earth is millions of years old due
to slow geological processes
 Lyell (1833) – released
Principles of Geology, which
explained that factors shaping
the ancient Earth are the same
that are presently acting on it
(volcanoes, erosion, etc.)
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Darwin’s Conclusion: If Earth could
undergo such changes, life could
do the same over long periods of
time
Darwin’s Influences
(1744-1829) – one of the 1st
scientists to recognize organisms change
over time
 Lamarck
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Thought that organisms “chose” to become more
complex (Bird learned to fly from an “urge”)
Believed that organisms could change based on
use or disuse of certain parts.
Believed that acquired traits could be inherited
(strength, speed, etc.)
For example, Mrs. Fernandez and Mrs. Wade worked
out for several weeks and acquired the coveted sixpack abs. Years later when Mrs. Wade had her fifth
child, he was born with the desirable abs.
Tendency towards perfection- continually changing to be
successful.
Darwin’s Influences
(1798) – reasoned that the human
population was growing faster than the
Earth’s resources could supply
 Malthus
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Darwin’s Conclusion: This must also apply to
other organisms since humans produce far
fewer offspring than other animals
 Some forces must keep population sizes in
check.
Darwin’s Theory
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1)
2)
3)
Darwin Published On the Origin of Species in
1859 after sharing similar ideas with a man
named Wallace.
His Theory included 8 major points:
Individual organisms have variation due to
inheritance ( differences in a population).
Organisms can only pass down the traits that
they are born with.
Organisms compete for limited resources.
Darwin’s 8 major points cont:
4)
5)
6)
7)
8)
Because of #1, each organism has different
advantages and disadvantages in their
struggle for existence.
“Best suited” individuals survive and
reproduce, passing on their genetic info and
leaving more offspring.
Species change over time
Species alive today have evolved from
previous species.
All organisms are tied together by common
descent.
Lamarck vs. Darwin
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http://www.angelfire.com/bug/darwinvsla
marck/
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Occurs in all populations
Sexual reproduction increases the chance
of natural variation because of the gene
shuffling of meiosis
Occurs far less frequently in asexual
reproduction
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The selective breeding of domesticated
plants and animals by man.
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Question:
What’s the ancestor of the domesticated
dog?
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Answer: WOLF
Natural Selection
Selection – traits among a
species are selected over time to benefit
the ability of organisms to survive and
reproduce
 Natural
Example of Natural
Selection: Evolution
of the European
Peppered Moth due to
the Industrial
Revolution
Natural Selection
 Organisms
are in a struggle for
existence, meaning they are in
competition for food, living space, mates,
etc.
 “Survival of the Fittest” - Those organisms
who are most “fit” will survive longer,
reproduce more, and pass their genes on
to offspring
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Fitness refers to the ability of an organism to
survive/reproduce.
An Adaptation is any change that increases
the organisms chance of survival
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A trait/characteristic that an organism is
born with
All organisms have adaptations that help
them survive and thrive
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Structural adaptations are physical features
of an organism
Behavioral adaptations are the things
organisms do to survive.
Physiological adaptations are chemical
responses to stimuli to maintain homeostasis
Descent With Modification
 Darwin
proposed that natural selection
acts to make organisms more diverse,
occupy different niches and habitats, and
look different than their ancestors.
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This is called Descent with Modification.
The idea of Common Descent hypothesizes
that all species were derived from common
ancestors.
Evidence for Evolution
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2)
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There are 5 major lines of evidence for
evolution:
Fossil Evidence
Geographical Evidence
Anatomical Evidence
Embryological Evidence
Biochemical Evidence
Fossil Evidence and
Geographical Evidence
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Fossil Evidence: Fossils have
formed in layers of rock to show
gradual changes over time.
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Fossils found deeper in sedimentary layers
are older and more simple;
Fossils found higher up in these layers are
younger and more complex
Geographical Evidence: Darwin
found animals similar in structure
& function in different parts of the
world, though their habitats were
similar.
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Organisms can be similar by descent from
ancestors, or they can look similar and be
completely unrelated.
Anatomical Evidence
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Anatomical Evidence: Some different organisms
have very similar body structures: Homologous
Structures.
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Example: limb structure in penguins, alligators, bats,
and humans
Vestigial Organs: organs that are no longer used by
an organisms (like the appendix)
Embryological Evidence and
Biochemical Evidence
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Embryological Evidence: Early
vertebrate embryos are very
similar at early stages of
development
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Biochemical Evidence: Certain
amino acid sequences of
proteins are very similar among
organisms
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Example: These diagrams show
Hemoglobin comparisons
between humans and other
organisms
Modern Evolutionary Biology
 Darwin
was unable to explain the source
of variation (genes) and how traits were
inherited.
 Using
Mendel’s and Darwin’s work,
Biologists have a much better idea of how
it all works.
Genetic Variation
A
Gene Pool include all the genes for all
the traits in a population.
 There are usually 2 alleles for each trait.
 Relative
Frequency describes the
percentage of a certain allele’s occurrence
in a population.
Genetic Variation
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Main Sources of Genetic Variation:
 Mutations
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Any change in the DNA sequence
Can be beneficial of harmful
Can affect organism’s phenotype (and fitness)
 Gene
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Shuffling
Shuffling of genes during production of
gametes in meiosis
“crossing over” during meiosis
Natural Selection and
Single-Gene Traits
 Single-gene
traits are those that are
determined by 2 alleles and produce 2
different phenotypes.
 Natural
Selection favors some traits more
than others, so phenotypes frequencies
will not always be 1:1.
Natural Selection and
Polygenic Traits
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Polygenic traits, traits that are determined by
more than 1 gene (like height), produce
phenotypes with a normal distribution (or bell
curve)
 Have many possible genotypes and
phenotypes.
Natural Selection and
Polygenic Traits
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Natural Selection can affect polygenic traits in 3
possible ways:
1)Directional Selection – when individuals at one
end of the curve have a higher fitness than the
other, the entire curve shifts in one direction.
Natural Selection and
Polygenic Traits
2) Stabilizing Selection – when
the median phenotypes
have better fitness, the ends
of the curve shift inwards
(the curve gets steeper)
3) Disruptive Selection – when
the extreme phenotypes
(ends of the curves) have
better fitness, the curve
begins to split in half.
*Can lead to speciation
Microevolution
 Microevolution
is simply a change in gene
frequency within a population. This change
is due to four different processes:
mutation, selection (natural and artificial),
gene flow and genetic drift.
 Ex.
Antibiotic and pesticide resistance.
Microevolution:
Genetic Drift
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Changes in the gene pool of a small population
due to chance.
 The smaller a population, the greater the chance of
deviations from the expected result.
 Founder Effect: an allele frequency change due
to a migration of a subgroup of a population
 Bottleneck Effect: disasters that reduce a
population size quickly and unselectively leave
behind organisms that are probably not
representative of the entire population’s genetic
makeup
Speciation
– the process of forming new
species from existing ones
 A species is defined as a group of
organisms that (1) interbreed and (2)
produce fertile offspring.
 These 2 conditions can be disrupted by 3
different types of Isolation:
 Speciation
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Behavioral Isolation
Geographic Isolation
Temporal Isolation
Speciation: Isolation
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Behavioral (Reproductive)
Isolation: 2 populations are
capable of mating but have
different courtship
procedures
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Geographic Isolation: 2
populations are separated
by a geological boundary
(mountain, river, highway)
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Example  Squirrel population
split by Colorado River 10,000
years ago
Example: Eastern
Meadowlarks will not
answer mating songs from
Western Meadowlarks
Speciation:Isolation
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Temporal Isolation: 2 or more species
reproduce at different times
Speciation Among Darwin’s Finches
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When observing the Galapagos Islands, Darwin noted
several different species of birds that all turned out to be
finches.
 These finches were thought to have come from an
ancestor who immigrated to the islands from the South
American mainland.
 Each species
has carved its own
niche on the islands
through natural
selection and many
speciations
(changes in beaks,
food, habitat, etc).
Macroevolution: A Major Factor
in Speciation and Evolution
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Macroevolution means large-scale evolutionary changes.
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It includes:
 Mass Extinctions – widespread extinction of many
organisms at one time (opens up new niches for survivors
resulting in MANY new species.
 Adaptive Radiation – when a single species evolves into
many different species
 Convergent Evolution – when 2 unrelated species adapt
homologous structures due to their habitats
 Coevolution – organisms that are closely connected to
each other evolve in response to one another
 Punctuated Equilibrium – long periods of little change
interrupted by short periods of rapid change.
How did Earth form?
 Chunks
of “rock” hitting each other in
space
 Heat generated and melted rock
 Elements rearranged themselves by
density
 4 billion years ago, rock cooled & water
could remain liquid – early oceans
The Early Earth
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A very volatile environment with poisonous
gases (HCN, CO2, CO, N2, H2S, ammonia, CH4,
and H2O)
 Some scientists believe that organic molecules
could have been created from inorganic
molecules combines with electricity (from
lightning).
 An attempt to show this idea was put forth by
Stanley Miller and Harold Urey in 1953.
The Miller-Urey Experiment
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Miller and Urey created a
simulation of the predicted
early atmosphere of the
Earth.
 When they combined the
atmospheric components
with electricity, they
produced organic
compounds including amino
acids.
The Evolution of Life
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Some scientists believe that RNA was the first
genetic information
 The first life forms are thought to be single-celled
prokaryotes (found from microfossils in rock)
similar to bacteria.
 Later, photosynthetic bacteria produced oxygen.
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This oxygen combined with iron in the water, forming
rust, which dropped to the ocean floor and left the
ocean blue-green
Most organisms evolved new metabolic pathways
that would allow them to live in the new oxygenrich environment.
The Evolution of Life
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Eukaryotic Cells evolved from prokaryotes that
began evolving internal cell membranes.
 Some small prokaryote then entered a larger
prokaryote to form a mutualistic relationship.
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These smaller prokaryotes were able to use oxygen
(aerobic respiration) and evolved into what is now our
mitochondria…recall that mitochondria have different
DNA than the rest of the cell.
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This is called the Endosymbiotic Theory.
 The evolution of Sexual Reproduction (meiosis)
allowed much more genetic variation among
eukaryotes.
The Endosymbiotic Theory
A
descriptive Diagram: