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Darwinian Evolution
Chapter 22
What you need to know!
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How Lamarck’s and other notable
predecessors’ views of the mechanism of
evolution differed from Darwin’s.
The difference between structures that are
homologous and those that are analogous,
and how this relates to evolution.
The role of adaptations, variation, time,
reproductive success, and heritability in
evolution.
Preceding Darwin
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Aristotle 384-322 BC – Scala naturae: oragnization of
life based on increasing complexity
Linnaeus 1707-1778 – taxonomy: naming and
classifying all organisms, binomial nomenclature: genus
and species
Cuvier 1769-1832 – father of paleontology, study of
fossils leads to theory of catastrophism (mass
extinction) which explains the boundaries between
strata and the location of different species
Preceding Darwin
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Hutton 1726-1797 &
Lyell 1797-1875 –
Theory of Gradualism
(uniformitarianism):
Earth geology
changes slowly and
continuously
The Earth must be
VERY old
Darwin studied Lyell’s
work
Preceding Darwin
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Lamark 1744-1829 – 1st theory of evolution
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Use or disuse of body parts leads to their
development or deterioration (acquired
characteristics)
Inheritance of acquired characteristics
Early Darwin
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5 year voyage on the HMS Beagle 18311836
Naturalist – collected plants, animals, and
fossils
Major finds on the Galapagos Islands
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Finches
Tortoises
Common ancestor
Late Darwin
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“Origin of Species”
Natural variation exists in all populations
All organisms produce many offspring with
variations
All organisms compete for limited resources
Natural Selection
Descent with modification
Artificial Selection
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Human selection of favorable traits over
100’s of generations
Darwin used this model to develop natural
selection and descent with modification
Natural Selection
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Darwin’s mechanism for evolution is natural
selection (an explanation for adaptations)
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What was Lamark’s mechanism?
Adaptations: characteristics that enhance an
organisms ability to survive (i.e. desert fox – large
ears; arctic fox – small ears)
Organisms that have advantageous heritable traits
(fitness) survive and reproduce at a higher rate
Environmental changes may result in adaptations,
and sometimes speciation (the founder effect)
Individuals do not evolve, Populations do!
Descent with Modification
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Offspring are genetically different from their
parents
As we move forward in time diversity
increases (speciation)
As we move backward in time diversity
decreases (fewer species)
If we go back far enough all species are
related (ancient common ancestor)
Evolution Summed Up
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Evolution is change in species over time.
Heritable variations exist within a population.
These variations can result in differential
reproductive success.
Over generations, this can result in changes
in the genetic composition of the population.
Individuals do not evolve! Populations do!
Patterns of Evolution
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Divergent Evolution
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Convergent Evolution
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Different species show the same
adaptations due to similar environments
(analogous structures)
Parallel Evolution
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2 different species evolve from a
common ancestor (different adaptations)
2 different animal groups evolve similarly
in separated environments (mammals
and marsupials)
Coevolution
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Both predators and prey adapt to each
other over time