History of Evolution

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History of Evolution

• James Hutton Charles Lyell
• Hutton - rocks are in layers, which form
  very slowly proposed that the Earth is
  millions of years old.
• Lyell - geological features were formed by
• processes that still occur today.
• mountain building, volcanoes, erosion,
  etc.

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Jean-Baptiste Lamarck

• He proposed that by selective use/disuse of
  organs, organisms acquired or lost certain traits
  during their lifetime.
• These traits could then be passed on to their
  offspring which, over time, led to change in a
  species.

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Lamarcks Key Ideas

• 1.) Tendency toward perfection.
• He believed that all organisms try to become
  perfect by acquiring traits that help them live
  more successfully.
• Ex In his view, the ancestors of birds had an
  urge to fly. Over many generations, they kept
  trying to fly, and their wings increased in size
  and eventually became good enough to allow flight.

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Lamarcks Key Ideas

• 2.) Use and Disuse
• Organisms can change the size and shape of parts
  of their bodies by using them in different ways.
• Ex By trying to use their front limbs for
  flying, birds eventually were able to change
  those limbs into wings.
• The reverse is also true, according to Lamarck

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Lamarcks Key Ideas

• 3.) Inheritance of Acquired Traits
• If an animal can change its body during its
  lifetime, its offspring will also have these
  changes.
• If an animal was able to change its body to get a
  longer neck (say, by stretching it), its
  offspring will also have longer necks.
• However, by this reasoning, if you were to chop
  off your arm, your children should be born
  missing an arm because they should inherit this
  trait.

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Evaluating Lamarck

• He was incorrect in many ways.
• He did not know how traits were inherited.
• He did not know that an organisms behavior has
  no effect on its inheritable characteristics.
• But, he was one of the first to develop a
  scientific hypothesis for evolution and realize
  that organisms are adapted to their environments.

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Darwin and Natural Selection
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Who was Darwin?

• Charles Darwin
• Naturalist
• Scientist
• Wanted to be a priest
• Quit medical school to study the Bible and become
  a priest, but became a naturalist instead.

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The Voyage

• 1831
• 5 year trip on the HMS Beagle around the world to
  study life forms.
• Stopped in Brazil, Peru, Ecuador, the Galapagos
  Islands, New Zealand, Australia

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His Observations

• Patterns of diversity.
• He saw similar ecosystems with very different
  looking animals.
• Ex Australia and Argentina have very similar
  grasslands, but the animals in each are very
  different.
• No rabbits in Australia no kangaroos in
  Argentina.

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His Book

• On the Origin of Species
• 1859
• Summarized the results of his voyage and later
  studies.
• Proposed a mechanism for evolution called natural
  selection
• Presented evidence demonstrating that evolution
  has been taking place for millions of years, and
  continues today in all living things.

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Controversy

• His book caused an immediate sensation (think
  The Da Vinci Code of its time.)
• Many people argued about his statements.
• Some people thought he was brilliant others
  thought he was an idiot/heretic.
• But, WHAT did Darwin actually say?

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Darwins Big Idea

• Natural Selection!!!!

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What is Natural Selection?

• It is a mechanism for change in populations that
  occurs when organisms with traits that allow them
  to survive better reproduce and pass those traits
  to their offspring.
• What happens to those organisms who dont have
  the favorable traits?
• They are less likely to survive and reproduce

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Natural Selection Summarized

• 1.) In nature, there is a tendency for organisms
  to produce more offspring than can possibly
  survive.
• Ex Fish

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Natural Selection Summarized

• 2.) In any population, individuals will have
  slight differences in their phenotypes.
• Ex Fish, zebras, snakes

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Natural Selection Summarized

• 3.) Individuals with traits that make them
  more likely to survive in an environment will
  survive and pass on those traits to their
  offspring.
• Fish, zebras and snakes again
• More of these individuals will survive as
  compared to those who do not have the helpful
  traits.

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Natural Selection Summarized

• 4.) Eventually, the offspring of the survivors
  will make up a larger part of the population.
• Depending on environmental factors, after many
  generations, the population may look completely
  different from what it originally was.

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Evolution by Natural Selection

• Struggle for existence
• Members of each species compete for resources.
• Faster or more skilled predators get more food
  faster prey or those with good camouflage get
  away and reproduce.
• Adaptations allow organisms to survive.

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Evolution by Natural Selection

• Survival of the fittest
• Those organisms best suited to their environment
  will survive those who arent will die.
• Descent with Modification
• Species today look different from their
  ancestors.
• Each species today has descended, with changes,
  from other species over time.
• All living things are related to one another.

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Adaptations

• Any trait that improves the chances of survival
  and reproduction is called an adaptation.
• Species develop adaptations through natural
  selection.

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Types of Adaptations

• Structural adaptations
• Physical features that help in survival.
• Ex thorns of a rose, camouflage, mimicry
• Physiological Adaptations
• Changes in an organism s metabolism
• Ex antibiotic-resistant bacteria pesticide-
  resistant insects

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Evidence for Evolution

• Fossil Record
• Fossils were known (even in Darwins time) to be
  the remains of ancient life.
• Also, it was known that different rock layers
  formed at different times in Earths history.
• Fossils that are in the different layers are of
  different ages the ones in deeper layers existed
  before the ones in more shallow layers.

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Evidence for Evolution

• Geographic distribution of living species
• Darwins travels
• Different animals on different continents
  descended from different ancestors.
• However, because animals on each continent were
  living in similar ecosystems and exposed to
  similar challenges and pressures, they developed
  similar body structures.

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Evidence for Evolution

• Homologous body structures
• Limbs of some organisms, for example, have
  different forms and functions, but are made of
  the same basic bones.
• The same bones in our arms are in the wings of a
  bird.

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Evidence for Evolution

• Compared Embryology
• Embryology is the study of embryos, the early
  stages of animal development.
• Early in development, the embryos of related
  animals are hard to tell apart.

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Genes and Variations

• How do we get variations in the gene pool?

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Sources of Genetic Variation

• 1.) Mutations
• 2.) Gene shuffling
• Due to sexual reproduction
• Remember in meiosis, chromosomes/genes separate
  (Principle of Segregation)
• Crossing over also leads to variation.
• Think about a deck of cards

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Traits

• The number of phenotypes for a given trait
  depends on how many genes control the trait.
• Single-gene trait vs. Polygenic trait.
• Single gene few variations
• Polygenic trait many variations

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Natural Selection and Traits

• N.S. on single gene traits can lead to changes in
  allele frequencies, which leads to evolution.
• Ex Effect of color mutations on lizard
  survival.

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Natural Selection on Polygenic Traits

• When traits are controlled by more than one gene,
  the effects of natural selection are more
  complex.
• Fitness is the key!

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Selection

• Natural selection can effect the distributions of
  phenotypes in 3 ways
• Directional selection
• Stabilizing selection
• Disruptive selection

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Directional selection

• Individuals at one end of a curve are more fit
  than other individuals.
• This shifts the curve in one direction.

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Stabilizing Selection

• Occurs when individuals near the middle of the
  curve are more fit.
• The center of the curve stays in the same place,
  but the curve becomes narrow.

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Disruptive Selection

• Individuals at the ends of the curve are more fit
  than those in the middle.
• Creates a double humped curve.

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Genetic Drift

• Natural selection is not the only source of
  evolutionary change.
• In large populations, probability can be used to
  predict genetic outcomes.
• In small populations, the laws of probability do
  not always work.
• Ex coin flip

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How Does Genetic Drift Happen?

• In small populations, individuals that carry an
  allele for a trait may leave more offspring
  (descendants) than those who dont have the
  allele, just by chance.
• Over time, a series of these chance happenings
  can cause an allele to be more common.

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Two methods of Genetic Drift

• Founder effect
• Bottleneck effect

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Founder Effect

• A change in the allele frequencies due to
  
• the migration of a small group of organisms
  
• to a new area.
• Ex Huntingtons in Venezuela
• Ex Type O blood in Native tribes in South
  America
• Ex The Amish and Microcephaly in
  Pennsylvania

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Founder Effect
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Bottleneck effect

• Change in allele frequencies due to a
  catastrophic event (natural disaster, disease,
  habitat destruction, etc.)

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Speciation

• The evolution of a new species.
• Geographical isolation can lead to this.

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2 Ideas on how evolution occurs

• Gradualism
• Evolution occurs SLOWLY over a long time.
• Adaptations will increase in number steadily over
  time.
• Darwins idea.
• Punctuated Equilibrium
• Speciation occurs in rapid bursts followed by
  periods of no change.

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How do scientists determine the age of fossils?

• Radioisotope dating
• Isotopes are atoms with different numbers of
  neutrons Carbon 12, Carbon 13, Carbon 14.
• Carbon 14 is the normal isotope used for dating
  fossils.
• By measuring the half-life of the isotope,
  scientists can determine the age.

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Major Ages in the History of the Earth
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Plants respond to the environment, too.

• Plants do not have nervous systems, but they do
  have the ability to respond to the environment.

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Ways plants adapt

• Geotropism
• Response of seedlings to the force of gravity.
• Causes roots to grow down and stems to grow up.
• Phototropism
• Ability of plant to respond to light.
• Thigmotropism
• Ability of plant to respond to touch.
• Climbing plants use this to find their way
  up/around an object.

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Geotropism
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Phototropism
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Thigmotropism
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Plant Hormones

• Auxins
• Responsible for regulating phototropism by
  causing cells to get longer.
• Gibberellins
• Cause plant to grow taller.
• Increase rate of bud formation and seed
  germination
• Abscisic acid
• Inhibit plant growth during times of stress.

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Plant Adaptations

• Seeds of some plants will go dormant in
  unfavorable conditions.
• Roots and stems are modified into storage organs.
• Conifers have needles instead of leaves, which
  prevent evaporation of water.
• Conifers also have thick bark which insulates
  them in the winter.
• Flowers can be pollinated in multiple ways wind,
  animals, birds, insects.