Ch. 5 Evolution

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Ch. 5 Evolution

• APES Mrs. Sealy

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I. Origins of Life

• How do we know?
• Chemical analysis chemists have conducted lab
  experiments to show how simple organic compounds
  could have been created.
• Radioactive dating radiocarbon, radiometric
  dating with radioactive rocks and fossils

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CH4
H2O
Water vapor
CO2
N2
Electrode
H2
NH3
Electrical sparks simulating lighting provide
energy to synthesize organic compounds
Condenser
Cold water
Cooled water containing organic compounds
H2O
Sample for chemical analysis
Fig. 5.3, p. 104
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• Life evolved in two phases over the course of
  4.7-4.8 billion years
• Chemical evolution of organic molecules and
  polymers
• Biological evolution from single celled
  prokaryotic bacteria to multi-cellular eukaryotic
  organisms

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Chemical Evolution

• Formation of the Earths Crust 4.6 to 4.7
  billion years ago a cloud of cosmic dust
  condensed into planet earth which soon turned
  molten due to radioactive decay and meteorite
  impacts. As cooling took place a thin crust
  developed.
• Formation of the earths seas volcanic eruptions
  and comet impacts brought water vapor that rained
  down on earth to create the sea

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Chemical Evolution (cont.)

• Small organic molecules form in the seas from
  eroded minerals from rocks
• 4.4 billion years ago the first atmosphere was
  formed. The main components were believed to be
  CO2, N2,H2O , CH4, NH3, H2S, HCL, no oxygen
• This mixture is often to as The primordial stew

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Chemical Evolution (cont.)

• Large organic molecules form in the seas energy
  from lightening, heat from volcanoes, and UV
  light and the chemicals in the atmosphere
  combined to form the first large organic
  molecules such as amino acids and carbs.
• Another theory is that these large molecules
  formed in hydrothermal vents.
• First protocells form in the seas these new
  compounds washed into the seas and sat for
  millions of years to form the first DNA and
  protocells

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Chemical Evolution (1 billion years)
Formation of the earths early crust
and atmosphere
Small organic molecules form in the seas
Large organic molecules (biopolymers) form
in the seas
First protocells form in the seas
Biological Evolution (3.7 billion years)
Single-cell prokaryotes form in the seas
Single-cell eukaryotes form in the seas
Variety of multicellular organisms form, first in
the seas and later on land
Fig. 5.2, p. 103
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Biological Evolution

• 3.5 to 3.8 billion years ago, well below the
  surface of the sea away from harmful UV radiation
  the first prokaryotic cells formed PROKARYOTIC
• 2.3 to 2.5 billion years ago the first
  cyanobacteria appear and they photosynthesize
• 2.0-2.1 billion years ago oxygen formed from
  cyanobacteria
• 1.2 billion years ago we see the first eukaryotic
  cells arrive, which could reproduce sexually and
  produce a wide variety of organisms
• 400-500 million years ago we see the first land
  plants and animals
• How do we know what organisms were around
• Fossil record
• Radiometric dating of rocks near the fossils

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Modern humans (Homo sapiens) appear about 2
seconds before midnight
Age of mammals
Recorded human history begins 1/4 second before
midnight
Age of reptiles
Insects and amphibians invade the land
Origin of life (3.63.8 billion years ago)
Plants invade the land
Fossils become abundant
Fossils present but rare
Evolution and expansion of life
Fig. 5.4, p. 105
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Which of the following was missing in the early
atmosphere?

1. Ammonia
2. Oxygen
3. Methane
4. Water vapor

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Where did the original O2 come from in the
atmosphere?

1. Lightening
2. Cyanobacteria
3. Chemosynthetic bacteria
4. UV light breaking down ozone

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Evolution

• Heritable changes in a populations genetic
  make-up through successive generations
• An overwhelming majority of biologists believe
  that this is the best explanation for the changes
  that have occurred over the last 3.7 billion
  years and also for why life on earth today is so
  diverse.
• The theory of evolution is based on the idea that
  all species descended from other species

http//www.hippocampus.org/Biology
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2nd Generation
1st generation
GG, Gg green beetle gg brown
beetle Evolution shift in gene frequency in a
population
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Evidence of Evolution
http//www.sumanasinc.com/webcontent/animations/co
ntent/evolution/evolution.html
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1. Biogeography

• Geographical distribution of species

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2. Fossil Record

• Fossils and the order in which they appear in
  layers of sedimentary rock (strongest evidence)

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3. Taxonomy
Classification of life forms.
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4. Homologous Structures
Structures that are similar because of common
ancestry (comparative anatomy)
Turtle
Alligator
Bird
Mammals
Typical primitive fish
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5. Comparative Embryology

• Study of structures that appear during embryonic
  development

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6. Molecular Biology

• DNA and proteins (amino acids)

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Macroevolution

• long term, large scale evolutionary changes among
  a group or species. One species leads to the
  appearance of many other species.

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• The Three Things needed For Evolutionary Change

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Genetic persistence

• The inheritance of DNA molecules from the origin
  of the first cells through all subsequent lines
  of descent which is the basis of the unity of
  life

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Genetic divergence

• Long term changes in lineages of species, which
  are the basis of the diversity of life

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Genetic losses

• The steady background extinction or relatively
  abrupt catastrophic loss of lineage

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A change in the genetic composition of a
population over successive generations

1. Evolution
2. Natural selection
3. Genetic persistence
4. Genetic losses

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The gene pool is..

1. 1.The genetic composition of an organism
2. 2.The genetic composition of a population
3. 3.The genetic composition of a community

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• Microevolution the small genetic changes that a
  population experiences
• How does microevolution work?

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• It is the development of genetic variability in a
  population
• A populations gene pool is the sum total of all
  genes possessed by the individuals of the
  populations species

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• Microevolution is a change in the species gene
  pool over time

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• Members of a population have different molecular
  forms of the same gene called alleles. Sexual
  reproduction leads to a shuffling of alleles. As
  a result each individual has a different
  combination of alleles. This is called genetic
  variability

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• Microevolution works through a combination of
  four processes
• Mutation, natural selection, gene flow, genetic
  drift

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Four causes of evolutionary change

1. Mutation fundamental genetic shifts.
2. Genetic Drift isolation ? accumulation of
   mutations
3. Founder Effect immigrant sampling bias.
4. Natural Selection differential reproduction of
   individuals in the same population based on
   genetic differences among them.

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Mutation

• The source for all new alleles (genes) is
  mutations, which are random changes in the
  structure of DNA molecules in a cell.
• Adaptation any genetically controlled trait that
  helps an organism survive and reproduce under a
  given set of environmental conditions
• Every so often a mutation is beneficial and the
  result is a new genetic trait that will ensure
  the survival of offspring better
• Mutations are rare

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Natural Selection

• Differential reproduction because of random
  shuffling or recombination of genes, certain
  individuals may by chance have one or more
  beneficial adaptations that allow them to survive
  under various environmental conditions. As a
  result they are more likely to reproduce than
  individuals that do not have such adaptations.

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Evidence of Natural Selection
http//www.sumanasinc.com/webcontent/animations/co
ntent/evolution/evolution.html
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• Natural selection does not create favorable
  genes instead it favors some individuals over
  others by acting on genes already in the gene
  pool.
• Natural selection occurs when the combined
  effects of adaptation and differential
  reproduction result in a particular beneficial
  gene becoming more common in succeeding
  generations

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Three types of Natural Selection

• Directional it pays to be different changing
  environmental conditions cause gene frequencies
  to shift so that individuals with traits at one
  end of the normal range become more common than
  midrange species

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Directional Natural Selection
Average
New average
Previous average
Snail coloration best adapted to conditions
Number of individuals
Number of individuals
Average shifts
Coloration of snails
Coloration of snails
Proportion of light-colored snails in population
increases
Fig. 5.6a, p. 110
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• Stabilizing it pays to be average in a stable
  environment species that have abnormal genes have
  no advantage and tend to be eliminated.

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Stabilizing Natural Selection
Dark snails eliminated
Light snails eliminated
Snails with extreme coloration are eliminated
Number of individuals
Number of individuals
Coloration of snails
Coloration of snails
Average remains the same, but the number of
individuals with intermediate coloration increases
Fig. 5.6b, p. 110
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• Diversifying it doesnt pay to be normal when
  environmental conditions favor individuals at
  both extremes of the genetic spectrum and sharply
  reduce the number of mid-range individuals.

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Diversifying Natural Selection
Snails with light and dark colors dominate
Intermediate-colored snails are selected against
Light coloration is favored
Dark coloration is favored
Number of individuals
Number of individuals
Coloration of snails
Coloration of snails
Number of individuals with light and dark
coloration increases, and the number with
intermediate coloration decreases
Fig. 5.6c, p. 110
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Gene Flow

• Movement of genes between populations

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Genetic drift

• involves change in a genetic composition of a
  population by chance and is important in small
  populations

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An Example of evolution by natural selection

• The peppered moths of England
• During the industrial revolution.
• http//www.echalk.co.uk/Science/Biology/PepperedMo
  th/Peppered_MothWEB.swf

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Founder Effect

• sampling bias during immigration. When a new
  population is formed, its genetic composition
  depends largely on the gene frequencies within
  the group of first settlers.

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Founder Effect.--
Human example your tribe had to live near the
Bering land bridge
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Founder Effect.--
to invade settle the New World!
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Small genetic changes within a population of a
species

1. Macroevolution
2. Co-evolution
3. Natural selection
4. Microevolution

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Mutations are .

1. Always occurring in patterns
2. Very common events
3. A source of new genetic material
4. Always harmful

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When natural selection results in a shift toward
one end of a normal range of traits

1. Continuous natural selection
2. Stabilizing natural selection
3. Directional natural selection
4. Disruptive natural selection

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The changes in coloration in the peppered moth is
a result of..

1. Co-evolution
2. Microevolution
3. Convergent evolution
4. macroevolution

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Co evolution

• When populations of two different species
  interact over a long time, changes in the gene
  pool of one species can lead to changes in the
  gene pool of the other species. For example

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Coevolution
Coevolution can occur between animals that have a
symbiotic relationship as well those who have a
predator prey relationship
Coevolution gone awry
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Ecological Niches and Adaptation

• Ecological niche the species way of life or the
  functional role of the species in an ecosystem.
  For example
• a. types of resources used
• b. range of tolerance
• c. how it interacts with components of the
  ecosystem
• d. its role in flow of energy and matter cycling

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Fundamental vs realized niche

• Fundamental niche vs. realize niche Your
  fundamental niche is all the possible conditions
  that you can live under. Your realized niche is
  how you are actually living. For example you may
  be capable being a star, but competition keeps
  you from getting the job

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Niche separation
Generalist species with a broad niche
Number of individuals
Generalist species with a narrow niche
Niche breadth
Region of niche overlap
Resource use
Fig. 5.7, p. 111
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Generalist species vs. Specialist species

• Generalist have very broad niches and eat a
  variety of foods and can live in a variety of
  places under differing conditions. For example
  cockroach
• Specialist narrow niche, may only be able to
  live in one type of habitat or eat only one type
  of food. For example panda bear
• Is it better to be a generalist or a specialist?

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An organisms niche is analogous to its

1. Address
2. Way of life
3. Food source
4. Trash dump

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The change in the gene pool of one species may
result in the change in the gene pool of another
species

1. Convergent evolution
2. Macroevolution
3. Co-evolution

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Is it better to be a generalist or a specialist?

1. Generalist
2. Specialist
3. Depends on stability of ecosystem

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Speciation

• Two species arise from one species in response to
  changes in environmental conditions.
• The mechanism for speciation occurs in two phases
• Geographic isolation occurs when two populations
  of a species becomes physically separated for
  long periods
• Reproductive isolation occurs as mutation and
  natural selection occur independently in two
  separated populations of the same species.
  Eventually, the changes are so great that two
  groups will no longer interbreed.

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Adapted to cold through heavier fur, short
ears, short legs, short nose. White fur matches
snow for camouflage.
Northern population
Arctic Fox
Spreads northward and southward and separates
Different environmental conditions lead to
different selective pressures and evolution into
two different species.
Early fox population
Adapted to heat through lightweight fur and long
ears, legs, and nose, which give off more heat.
Southern population
Gray Fox
Fig. 5.8, p. 113
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Convergent evolution

• Two separate species will evolve separately to
  create animals with similar characteristics.
  Species that have similar niches tend to evolve
  similar sets of traits in response similar
  environmental conditions. For example

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Divergent evolution speciation creates separate
species
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Extinction

• When environmental changes occur species either
  evolve or cease to exist and their genetic
  material is permanently lost.
• Extinction patterns have been caused by
  large-scale movements of the continents and
  gradual climate changes like those from meteors
  and volcanoes.
• All species inevitably disappear
• Background extinction is the low rate that
  species constantly disappear. It is the normal
  level. Approx.
• 3 species per year
• Mass extinction an abrupt rise in extinction
  rates above the background rate. It is
  catastrophic, global and often results in 25 to
  70 loss of species
• There are have been five previous mass
  extinctions and we are currently in the six mass
  extinction, which is being caused by humans.

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• Speciation minus extinction equals biodiversity
• Although extinction is a natural process, humans
  have sped up the process and we have lost a lot
  of genetic material
• This mass extinction is different from previous
  extinctions in the following ways
• 1. First time it has ever been caused by one
  species
• 2. This is the fastest it has every happened
• 3. Adaptive Radiation will be slow after because
  we are destroying habitats

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Species and families experiencing mass extinction
Bar width represents relative number of living
species
Millions of years ago
Period
Era
Current extinction crisis caused by human
activities. Many species are expected to become
extinct within the next 50100 years.
Extinction
Today
Quaternary
Tertiary
Cenozoic
Extinction
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Cretaceous up to 80 of ruling reptiles
(dinosaurs) many marine species including
many foraminiferans and mollusks.
Cretaceous
Jurassic
Extinction
Mesozoic
180
Triassic 35 of animal families, including many
reptiles and marine mollusks.
Triassic
Extinction
250
Permian 90 of animal families, including over
95 of marine species many trees, amphibians,
most bryozoans and brachiopods, all trilobites.
Permian
Carboniferous
Extinction
Devonian 30 of animal families, including
agnathan and placoderm fishes and many
trilobites.
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Devonian
Paleozoic
Silurian
Ordovician
Extinction
Ordovician 50 of animal families, including
many trilobites
500
Fig. 5.10, p. 115
Cambrian
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Adaptive Radiation

• Adaptive radiation an extinction of one species
  is an opportunity for another species and after a
  mass extinction there is a period in which
  numerous new species can evolve
• Speciation and extinction affects biodiversity

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Cenozoic
Mesozoic
Marsupials (kangaroos, etc.)
Rabbits
Rodents
Primates
Bats
Insectivores
Carnivores
Whales
Even-toed hoofed mammals
Odd-toed hoofed mammals
Elephants
Monotremes (platypus, etc.)
Fig. 5.11, p. 116
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How does Macroevolution occur?

• A. Macroevolution is concerned with how evolution
  takes place above the level of species and over
  long periods of time and shows how small changes
  can lead to the eventual creation of many
  different species, genera and families.
• B. Gradualist model theory that says macro
  evolutionary change occurs over many millions of
  years
• C. Punctuated Equilibrium opposing theory that
  says there are long periods of relatively
  punctuated with brief periods of very rapid
  changes.
• D. In reality it is probably a combination of both

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Punctuated Equilibrium

• Rate of speciation is not constant
• rapid bursts of change
• long periods of little or no change
• species undergo rapid change when they 1st bud
  from parent population

Time
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Gradualism

• Gradual divergence over long spans of time
• assume that big changes occur as the accumulation
  of many small ones

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Common Misconceptions about Evolution

• Survival of the fittest is often misinterpreted
  as survival of the strongest. In biological
  terms fitness is a measure of reproductive
  success and the ones with the most descendants
  are the fittest. Natural selection is not "tooth
  and claw competition.
• Humans evolved from apes, this is not true.
  Apes and humans have a common ancestor from which
  both are descended.
• Nature has a grand plan in which species become
  progressively more perfect, natural selection is
  random and there is no goal of perfection.

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• 1) Before 5 mya In Africa, our ancestral lineage
  and the chimpanzee lineage split.
• 2) Before 4 mya The hominid Australopithecus
  anamensis walked around what is now Kenya on its
  hind legs.
• 3) gt3 mya Australopithecus afarensis (Lucy)
  lived in Africa.
• 4) 2.5 mya Some hominids made tools by chipping
  stones to form a cutting edge. There were perhaps
  four or more species of hominid living in Africa.
• 5) 2 mya The first members of the Homo clade,
  with their relatively large brains, lived in
  Africa
• 6) 1.5 mya Hand axes were used. Also, hominids
  had spread out of Africa and into much of Asia
  and Europe. These hominids included the ancestors
  of Neanderthals (Homo neanderthalensis) in Europe
  and Homo erectus in Asia.
• 7) 100,000 years ago Human brains reached more
  or less the current range of sizes. Early Homo
  sapiens lived in Africa. At the same time, Homo
  neanderthalensis and Homo erectus lived in other
  parts of the Old World.
• 8) 50,000 years ago Human cultures produced cave
  paintings and body adornment, and constructed
  elaborate burials. Also, some groups of modern
  humans extended their range beyond Africa.
• 9) 25,000 years ago Other Homo species had gone
  extinct, leaving only modern humans, Homo
  sapiens, spread throughout the Old

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