EVOLUTION BY NATURAL SELECTION

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EVOLUTION BY NATURAL SELECTION

• A scientific view

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Theory

• EVOLUTION A HERITABLE CHANGE IN THE
  CHARACTERISTICS WITHIN A POPULATION FROM ONE
  GENERATION TO THE NEXT THE DEVELOPMENT OF NEW
  TYPES OF ORGANISMS FROM PREEXISTING TYPES OF
  ORGANISMS OVER TIME

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Theory of Evolution The Pattern

• (Descent with modification)
• 1) Species existing today have descended from
  preexisting species (i.e. are related)
• 2) Species are modified or changed over time.
• What is the scientific evidence?

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Types of Fossils
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Theory of Evolution The Pattern

• Evidence
• Age of the Earth and living things
• Extinction
• Transitional forms (missing links) and
  succession
• Environmental changes
• Changes in species
• Vestigial traits
• Real time observations

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Succession of Species
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Transitional Forms
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Change over time
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Theory of Evolution The Pattern

• Evidence that species are related comes from
  studies involving
• Geographic relationships
• Homologies

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Theory of Evolution The Pattern

• Scientists use homologies or similarities due to
  common ancestry
• Structural morphological traits. Ex the
  limbs of vertebrates have the same number and
  arrangement of bones but different functions,

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Structural Homology
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Theory of Evolution The Pattern

• Homologies contd
• Developmental Ex. the embryo and the fate of
  embryonic tissues, how organs are formed, fig
  24.8.

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Developmental Homology
Fig 24.8
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Theory of Evolution The Pattern

• Homologies contd
• Genetic Most recent method investigating the
  similarities of
• DNA sequence of certain genes
• Amino Acid sequence/composition of proteins.
• Other mitochondrial DNA, the genetic code,
  developmental genes (Evo-Devo).

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Genetic Homology
Fig 24.7
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Theory of Evolution The Pattern

• How do scientists determine if similar
  characteristics are homologous or analogous?
• Construct a phylogeny a family tree.
• Compare the occurrence of the trait (and other
  traits) in members of the tree.

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Phylogeny of Developmental Genes in Animals
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Phylogeny of Reptiles Mammals
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Theory of Evolution the Process

• What is the Process? Natural Selection
• Proof of Natural selection - 4 postulates or
  assumptions

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Figure 24-10
If heritable variation
A1A1
A1A1
A1A2
A1A2
A1A2
A1A2
A2A2
A2A2
A1A1
A2A2
Color varies among individuals primarily because
of differences in their genotype
leads to differential success
A1A1
A1A2
A1A1
A2A2
Birds find and eat many more dark-winged moths
than light-winged moths
then evolution results.
Allele frequencies have changed in the surviving
moths
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The Nature of Natural Selection

• Selection certain individuals in a population
  are better able to reproduce due to some
  characteristic adaptation.
• Adaptation due to a heritable trait that
  increases the fitness of a population in a
  certain environment, long term.
• Acclimatization physiological change in an
  individual in response to a change in the
  environment, short term and reversible (i.e.
  these changes are not heritable).

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The Nature of Natural Selection

• Evolution the population changes over time
  because of the higher reproductive rates in
  adapted individuals.
• Individuals do not adapt to a change in the
  environment!

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The Nature of Natural Selection - Misconceptions

• Evolution is not progressive.
• Organisms do not necessarily become better or
  more complex. Ex parasites.
• Phylogenies are trees not ladders,. Organisms
  that appear to be less complex may represent the
  form that best survives in their environment.

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Figure 24.15
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The Nature of Natural Selection

• Not all traits are adaptive.
• Do not help the organism survive or reproduce.
  Ex. vestigial traits and holdovers.
• Adaptation is limited by
• Genetic constraints
• Historical constraints

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The Nature of Natural Selection

• Genetic constraints
• Natural variation does not exist in the
  population, Ex. regeneration of body parts.
• Selection for an optimal trait is associated with
  selection for a suboptimal trait, ex. Galapagos
  finches beak size and shape.

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The Nature of Natural Selection

• Historical constraints
• The design of some body parts is limited by the
  availability of starting materials. Ex, middle
  ear bones.

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The Nature of Natural Selection

• Animals do not do things for the good of the
  species.
• There are often fitness trade-offs.