UNIT FIVE

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UNIT FIVE Evolution

• Main Idea How have species changed over time?
  (long periods of time)

Darwin and Mechanisms of Evolution The theory
and why it works
Click on image for Brain pop video on Darwin 420
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Evidence of Evolution The Fossil Record

• Indicates life began 3 bya
• Prokaryotes then Eukaryotes then multicellular
  Eukaryotes
• Fossil record determines
• When species appeared
• The type of environment
• When/if species became extinct

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• Fossils found in the rock layers are similar in
  some layers, but different in other layers. This
  shows us that the species had changed over time.
• Remember that the oldest rock layers are below
  the youngest rock layers

YOUNG
OLDER
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What does the theory of evolution say?

• Theory b/c lots of evidence
• Tested and re-tested by many scientists
• States that
• Variations in individuals can lead to changes in
  whole species

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It is believed that evolution does not
necessarily produce any long-term progress in any
one direction. Instead, evolutionary changes
appear to be more like the growth of a bush.
Turn to pg 81 of your RB

• 1. Trunk an ancestor common to all organisms
  represented on the tree.
• 2. Branches ancestors common to species at the
  ends of the branches.
• 3. Buds of the tree species that are alive
  today.
• Branches without buds at the ends species that
  have died out (or have gone extinct).

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Video How Does Evolution Really Work? 6 min
Charles Darwin did not only suggest that species
evolved. He also suggested how evolution might
have occurred. Lets travel to Ecuador to see how
the process of natural selection operates in
populations of rainforest hummingbirds .

• The theory and why it works

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Evolution Video (2122min)
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Natural Selection The Idea Behind the Theory
http//www.brainpop.com/science/ecologyandbehavior
/naturalselection/

• Evolution controlled by NATURAL processes
• THE PROCESS IS
• LIVE BREED PASS ON GENETIC INFO
• SURVIVAL OF SPECIES
• Survival of Fittest
• Those best ADAPTED will be able to DO THE PROCESS

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Results of Natural Selection

• Short term result
• Best fit (adapted) will pass on GOOD genes to
  offspring
• Long term result
• Change in frequency (number) of certain traits
• Which do you think will increase in frequency
  GOOD OR BAD?
• GOOD OF COURSE!
• As more individuals have good trait, species is
  evolving

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What drives evolution?

• Interactions between individuals and the
  environment
• OVERPRODUCTION
• STRUGGLE FOR SURVIVAL
• GENETIC VARIATION
• SELECTION BY THE ENVIRONMENT

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Evolution Cause 1
OVERPRODUCTION

• POTENTIAL TO PRODUCE MORE OFFSPRING THAN WILL
  SURVIVE
• This means the best fit individuals will
  survive, grow and reproduce.
• EX DEER, FISH

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Evolution Cause 2 STRUGGLE
FOR SURVIVAL

• Overproduction leads to STRUGGLE within species
• Only some live to reproduce
• Competition for resources
• Best competitors will live and breed
• Must STRUGGLE with environment also (disease,
  predators, temp changes etc)
• Those that withstand will survive!

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• Competition
• Not all offspring live long enough to reproduce.
  
• All the offspring will have to cope with
  environmental conditions such as temperature,
  disease, parasites, and predators.
• If they are to survive, they must compete for
  limited resources.
• Those that are best suited for the environment
  are more likely to survive and pass on their
  genes.

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Evolution Cause 3 GENETIC
VARIATION

• Variation must exist within survivors
• Ex Longer legs, bigger claws, diff. fur color
• Favored traits will stay in population and lead
  to evolution
• Adaptive Value
• Describes a trait that helps an individual
  survive in a particular environment
• EX polar bears have black skin the black skin
  has adaptive value b/c it helps them survive

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• The differences among offspring are due to
  genetic variation, the unique combination of
  traits that each organism inherits from its
  parents.
• Organisms that reproduce sexually have more
  variation, than those who reproduce asexually!

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Evolution Cause 4 SELECTION
BY ENVIRONMENT

• Traits w/ adaptive value benefit those
  individuals
• If reproduce, offspring have traits too
• Eventually, of individuals with trait
  increases, and most all will have it!
• Therefore, adapting to environment DRIVES
  EVOLUTION!

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Evolutionary (Phylogenic) Trees Animals
COMMON ANCESTOR
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Comparison of Human and Chimp Chromosomes
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Variation and Evolution

• Why differences among a popn are good!

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• To evolve, variations must exist in a species
  BEFORE the environment changes. They do not get a
  trait just because it is needed.

Click on the peppered moth to see how
environmental change drives evolution . 205 min
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A. Review of Variation

• Order of DNA bases determines traits
• Changes can occur that can change individual
• Two possible ways changes occur
• Mutations
• Genetic Shuffling (Recombination)

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B. Mutations

• Are random (cannot be predicted)
• Caused by radiation and chemicals
• To be passed on
• Single celled organisms (mitosis)
• Sex cells of multicellular organisms

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Mutations cont

• Most mutations harmful
• Some are beneficial (have adaptive value)
• These get passed on ?
• Ex polar bears probably didnt always have
  black skin mutation caused it and it was
  beneficial
• THIS IS MAIN SOURCE OF NEW VARIATION

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C. Genetic Shuffling

• Sorting and recombination of genes new combos
  of genes
• Think deck of cards deck always the same but
  each hand is different
• Sexual reproduction uses 2 decks so even more
  variation
• THIS IS MAIN SOURCE OF VARIATION WITHIN A SPECIES

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Results of Genetic Variation

• Types
• Structural changes
• Functional changes
• Behavioral changes

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A. Structural Changes

• Result of organisms entire history
• Ex polar bears vs other bears
• Homologous Structures
• Evolution helps explain structural similarities
• Ex (Arm structure) Humans, whales, birds and
  bats (see RB p88)
• All have 1 long bone, 2 shorter ones, and 5
  digits
• Tells us they all had a common ancestor
• These are homologous structures!

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Embryology
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Structural Changes cont

• 2. Vestigial Structures
• Structures that are present but no longer in use
• EX Snakes contain tiny, non-functional leg
  bones which suggest it evolved from 4-legged
  lizards

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Vestigial Structures(click link)
Pelvic bone in humans
Hind leg limbs in whales
Appendix in humans
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B. Functional Changes

• Molecular change
• EX
• All muscles produce tiny electric current
• Eels have developed stronger current to help them
  find food and kill prey

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C. Behavioral Changes

• Adaptive changes that increase reproductive
  success
• EX
• Fighting among males to win female
• Rhythms of bird calls
• Rates blinking in lightning bugs

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Importance of Variation

1. Environment changes, organisms have to adapt
2. Without variation, species likely to become
   extinct
3. If diversity lost, difficult to recover
4. Endangered species have small populations with
   little variation
5. If environment changes, they cannot adapt

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The Rate of Evolution and Extinction

• What affects how fast organisms evolve?
• What leads to extinction?

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Change is Everything!

• Change in environment Change in species!
• Failure to adapt to changes possible extinction
  ?

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Rate of EvolutionWhat affects how fast a species
evolves?

• Rate of environmental change
• Rate of reproduction

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A. Rate of Environmental Change

• Rapid environmental change rapid change in
  species
• Rapid change
• Ex. Modern horse many changes over past million
  years
• Slow change
• Ex. Horseshoe crab nearly identical to
  ancestors from 300 mya

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• Environmental Change cont
• Creation of new species can occur if species are
  separated by geography such as water or land
  features.

Geographic isolation of squirrels on opposite
rims of the Grand Canyon.
Harris's antelope squirrel inhabits the canyon's
south rim (left). Just a few miles away on the
north rim (right) lives the closely related
whitetailed antelope squirrel .
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B. Rate of Reproduction

• The of offspring produced can tell us how
  quickly a species can evolve
• Few offspring longer life slow evolution
• Ex. Humans, elephants
• Many offspring shorter life quicker evolution
• Ex. Bacteria, single celled orgs, fish

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Lets look at bacteria

• Reproduce very quickly
• See page 90 figure 5-6
• Millions exposed to antibiotic
• Very good chance a few will have resistant gene
  due to random mutation
• These will live, THEN pass on resistance
• Pretty soon, large population that have this
  resistance
• If same antibiotic used again, will increase
  resistance
• Soon, a SUPER STRAIN of this bacteria has evolved

http//www.sumanasinc.com/scienceinfocus/sif_antib
iotics.html
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Refer to RB page 90 figure 5-6
Brain Pop link
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Lesson learned

• Only use antibiotics when necessary
• Many strains are resistant to penicillin, the
  first antibiotic used
• Humans are creating Super Strains with continued
  misuse of antibiotics
• Similar occurrences with insects and insecticides

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What causes extinction?

• Death rate higher than birth rate
• Usually due to rapid env. changes
• These env. changes cause major drop in popn size
  if species cannot adapt
• Variation drops!
• Less variation to pass on
• Offspring essentially inbreeding, variation drops
  even more
• NO VARIATION
• NO ADAPTIVE VALUE
• EXTINCTION