GOALS FOR THIS LECTURE

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• GOALS FOR THIS LECTURE
• Review the major evidence presented by Darwin.
• Review concept of Natural Selection.
• Study several cases of natural selection in
• natural populations (evolution in
  action).
• Begin to learn the principles of constructing
• evolutionary trees.

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• DARWINS MAJOR EVIDENCE
• FOSSIL RECORD OF EXTINCT ORGANISMS
• HOMOLOGOUS STRUCTURES
• VESTIGIAL ORGANS OR STRUCTURES
• TRANSITIONAL FORMS
• ECOLOGICAL DIVERSITY OF ENDEMIC FAUNAS
• HIGHLY MODIFIED DOMESTIC SPECIES DUE TO
• SELECTIVE BREEDING.
• SIMILARITY OF EMBRYONIC STRUCTURES.

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DARWINS MECHANISM NATURAL SELECTION
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1. Individuals within species are
variable. 2. Some of this variation is passed
on to offspring. That is, it is
heritable.
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3. In every generation, more offspring are
produced than can survive.
This implies some kind of struggle for
existence or competition among
individuals.
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4. Survival and reproduction are nonrandom with
respect to some variable and heritable
traits in the population. Those individuals
who are better at surviving and/or
reproducing are said to have higher fitness
relative to the others. Enhanced
fitness stems from specific traits. The
extent or proportion of these traits changes
in the next generation due to enhanced
reproductive success of their carriers.
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• Natural selection acts on phenotypes, but
  evolution
• consists of (or is measured by) changes in
  allele frequencies
• in populations.
• 2. Natural selection is backward looking, not
  forward looking.
• 3. Natural selection can produce new traits even
  though it can
• only act on existing traits.
• 4. Natural selection acts on individuals, not
  groups.

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Natural selection does not lead to perfection.
Or, put in other words, adaptation is often a
process of improvisation.
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Natural selection is non-random, but it is not
progressive or goal-directed. The concept of
fitness is not inherently circular.
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Evolutionary changes in ground finch beak sizes
in response to changes in food resources---a
particularly well-studied case of evolution in
action.
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Which feature has changed the most relative to
the starting values?
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Guppy, Poecilia reticulata (formerly Lebistes
reticulatus). Range Trinidad, other offshore
islands, n. Venezuela a popular aquarium fish
feral populations all over the world. Males in
natural populations are highly and individually
polymorphic in color pattern.
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HIGH PREDATION
LOW PREDATION
PREDATION MOSTLY BY PRAWNS, WHICH ARE
INSENSITIVE TO RED LIGHT.
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