Darwins Theory of Evolution

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Darwins Theory of Evolution

• 1) Descent with modification all species
  descended from ancestral species.
• 2) The mechanism of evolution is natural
  selection of heritable traits.

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Logic behind Darwins theory
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Observations and Inferences

• Observation All populations have the capacity to
  increase in numbers
• Observation No population can increase
  indefinitely
• Inference Eventually the individuals of a
  population will end up competing for resources

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Observations and Inferences

• Observations All individuals have the same
  genes that specify the same assortment of traits
  and Most genes occur in different forms (alleles)
  that produce different phenotypes
• Observation heritable variations exist.
• Inference Some phenotypes compete better than
  others unequal reproductive success (natural
  selection)

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Natural Selection

• A difference in the survival and reproductive
  success of different phenotypes
• Acts directly on phenotypes and indirectly on
  genotypes

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Inference Natural selection leads to
evolutionary adaptation.
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Comparative Morphology

• Study of similarities and differences in body
  plans of major groups
• Puzzling patterns
• Animals as different as whales and bats have
  similar bones in forelimbs
• Some parts seem to have no function

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Comparative Development

• Each animal or plant proceeds through a series of
  changes in form
• Similarities in these stages may suggest
  evolutionary relationships

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Comparative Biochemistry

• Kinds and numbers of biochemical traits that
  species share is a clue to how closely they are
  related
• Can compare DNA, RNA, or proteins
• More similarity means species are more closely
  related

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Comparing Proteins

• Compare amino acid sequence of proteins produced
  by the same gene
• Human cytochrome c (a protein)
• Identical amino acids in chimpanzee protein
• Chicken protein differs by 18 amino acids
• Yeast protein differs by 56

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Molecular Clock

• Assumption Ticks (neutral mutations) occur at
  a constant rate
• Count the number of differences to estimate time
  of divergence

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Modern definition of evolution
Microevolution

• generation to generation change in a population's
  frequency of alleles.

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Genetic Equilibrium

• Allele frequencies at a locus are not changing
• Population is not evolving

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Conditions forHardy-Weinberg Equilibrium

• very large population size
• no migration
• no mutation (or no net mutation)
• random mating
• no selection (and no natural selection)

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Mechanisms of Evolution

• Mutation
• Gene Flow
• Genetic Drift
• Bottleneck Effect
• Founder Effect
• Natural Selection
• Nonrandom mating

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Change over Time

• Over time, the alleles that produce the most
  successful phenotypes will increase in the
  population
• Less successful alleles will become less common
• Change leads to increased fitness
• Increased adaptation to environment

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Adaptation to What?

• Relationship between adaptation and the
  environment isnt always direct
• Llamas of the Peruvian highlands have
  oxygen-efficient hemoglobin
• So do llamas close relative, the dromedary camel
• Trait was present in shared ancestor