Chapters 13

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Chapters 13 14

• Evolution
• Evidence of Change (13)
• How Change Occurs (14)

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Definition of Evolution

• A change in species of organisms over time.
• A process by which modern organisms have
  descended from ancient organisms.
• The Theory of Evolution is credited to Charles
  Darwin.
• Were actually many scientists who developed
  theories about evolution and contributed to the
  modern theory.

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Early Scientists

• deLamarck (1800)
• Major points to his ideas
• A desire to change
• Organisms change because they have an inborn urge
  to become better suited to their environment.
• Use disuse
• Organisms could cause changes in their own
  bodies.
• Inheritance of acquired traits
• Changes in bodies could be inherited.

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• 2. Darwin
• Overproduction
• All populations of organisms tend to
  overpopulate.
• Struggle for Existence
• Not all individuals survive.
• Variation
• Individual differences occur in all populations.
• Survival of the Fittest
• Those individuals with traits best suited to the
  environment survive (passing their traits on to
  their offspring).
• Evolution of a Population
• Population as a whole becomes better fit for
  the environment.

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deLamarck Darwin Compared

• deLamarck
• Populations of organisms all the same (no
  variations).
• Changes occur in the environment.
• Organisms can change in response to environment.
• All organisms survive.

• Darwin
• Populations of organisms with individual
  differences (variations).
• Changes occur in the environment.
• Environment selects for or against certain
  variations.
• Not all organisms survive.

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Darwins Evidence

• In 1831, Darwin was hired as a naturalist (person
  who studies nature) aboard the HMS Beagle. The
  voyage would last 5 years and travel around the
  world.
• At each stop Darwin collected specimens of
  plants, animals, rocks and fossils. He also kept
  detailed observations about the specimens and the
  environment.
• Darwin also studied 3 books 1 written by his
  grandfather about differences in individuals, 2
  C. Lyells book about geological events, 3
  written by Malthus about human population
  outgrowing the environment.

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• When Darwin returned to England he studied how
  farmers used selective breeding to improve
  livestock herds and crop plants.
• It took Darwin almost 30 years after his return
  to write his book The Origin of Species by
  Natural Selection.

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Adaptation

• Process by which populations of organisms become
  better fit (suited to their environment).
• Organisms that are fit live longer and produce
  more offspring (pass on their genetics).
• Darwin used the term adaptation to describe any
  inherited characteristic that increases an
  organisms ability to survive.

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Modern Evidence in Support of Darwins Theory
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1. Fossil Record

• From fossils, scientists have put together a
  geologic time scale (earth history).
• Relative dating determining the age of a rock
  by comparing it to other fossils in rock layers
  above or below.
• Absolute dating using the rate of decay
  (half-life) of radioactive elements (Carbon-14,
  Uranium-235, etc.) to determine the age of a
  fossil.

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2. Comparative Embryology

• Comparing the similarities and differences
  between embryos of different species at early
  stages of development.
• The more closely related species differences do
  not appear until very late stages of development.
• The less closely related species are the earlier
  differences appear.

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3. Comparative Anatomy

• Anatomy body structure.
• Homologous structures are similar in structure
  function.
• The greater the similarities the more closely
  related 2 species are.
• Vestigial organs organs that have no known
  function (Ex ?).

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4. Comparative Biochemistry

• Chemical makeup of compounds.
• Typical compounds used are DNA, ATP, Hemoglobin,
  and other proteins.
• More similarities in chemical composition the
  more closely related 2 species are.

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Conclusions

• The types of organisms present at a given period
  of the earths history have changed.
• Some organisms are no longer living on earth
  (extinct).
• As the number of similarities between species
  increases the more closely related the two
  species.

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Problems of the Fossil Record

• Not Complete fossils occur by chance when
  organisms do not decay (trapped in sediments, tar
  or tree sap), most organisms decay without
  forming a fossil.
• Quality preservation varies only part of
  body, footprints or impression may be fossilized.
• Age determining the age of a fossil is not
  exact ages are usually approximates and not
  absolute.

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Recent Evidence of Evolution

• Peppered Moths ? Before the Industrial Revolution
  in England peppered moths were mostly light brown
  but a few were dark. During daylight moths rested
  on tree trunks which were light colored. During
  the I.R. soot from burning coal coated trees. How
  did the population of moths change?
• Frequency of light colored moths in the
  population decreased.
• Frequency of dark moths decreased.

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• 2. Antibiotic Resistant Bacteria ?
• Has occurred in the last 80 years.
• Misuse overuse of antibiotics have contributed
  to the problem.
• Are several strains of bacteria that have become
  resistant.
• Examples include bacteria that cause gonorrhea,
  TB, and Staph infections.

Staph infection (Flesh-eating Bacteria)
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• 3. Insect Resistance to Pesticides ?
• Resistant genetics is present in a small number
  of insects in a population.
• When pesticides are not rotated, the percentage
  of resistant insects in a population increases.

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• 4. Weed Resistance to Herbicides ?
• Herbicide are not known to directly cause the
  genetic change that allow resistance.
• Resistance is present in the population.
• When the same herbicides are used over several
  seasons, the resistant weeds survive and a
  greater percentage of the population are
  resistant.

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Sources of Variation in Populations

• Genetic Recombination
• Organisms that reproduce sexually inherit ½ of
  their genes from each parent, this increases
  variation in individuals (individual
  differences).
• 2. Mutations
• Changes in DNA or chromosomes create variation in
  individuals.

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Important Points to Remember

• Changes occur in populations not in individual
  organisms.
• Adaptations only occur if individual differences
  can be passed on to offspring (inherited).
• Evolution is any change in the relative frequency
  of a gene pool of a population.
• Evolutionary changes only occur in response to
  changes in the environment.

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Important Terms

• Evolutionary Fitness ? success organism has in
  passing its genes on to the next generation.
• Adaptation ? any genetically controlled
  characteristic of an organism that increases its
  fitness.
• Species ? group of organisms that interbreed in
  nature and produce fertile offspring.

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Speciation development of a new species.

• Occurs when 2 populations are isolated
  (separated) cannot interbreed.
• 2 populations undergo different changes based on
  the variations in each population.
• After long term separation the 2 populations may
  develop reproductive barriers (reproductive
  isolation).
• Once reproductive isolation has occurred the 2
  populations are considered separate species.

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Reproductive barriers

• Different breeding seasons.
• Different courtship rituals.
• Habitat isolation.
• Offspring not viable (do not live).
• Offspring sterile.
• Gametes will not fuse. Fertilized egg not viable
  (will not develop).

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Geographic barriers isolate populations.

• Rivers
• Mountains
• Oceans
• Canyons
• Roads
• Housing additions

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Modifications to Darwins Theory
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Unchanged Gene Pools

• Some gene pools remain relatively unchanged for
  long periods of time. Requires
• No major changes in the environment.
• Species is well adapted.
• No competition by invading species.

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Genetic Drift

• A random change in the frequency of a gene in a
  gene pool.
• Occurs when there is a random environmental event
  (eruption of a volcano).
• Implies that not all characteristics contribute
  to fitness.

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Punctuated Equilibrium

• Long periods in which there is not change in a
  population followed by short periods of rapid
  change. (Ex peppered moths)
• Is still a controversial theory.
• May result from dramatic changes in climate.