Transcript Natural Selection and Evolution

Natural Selection and Evolution
Assumptions of Darwin
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1. offspring vary
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2. some of this variation is heritable
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3. more offspring are born than can
survive
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4. populations do not generally increase
in size
Inferences of Darwin
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1. individuals of the same species will
compete
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2. the survivors will pass on their
‘favourable’ traits to the next generation
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3. over time there will be more traits from
the survivors in the population
… This is natural selection.
Examples of Natural Selection
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a leaf-like praying mantis
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peppered moths in
pre- and postindustrial England
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mimicry of the
poisonous coral
snake by the nonpoisonous king
snake
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Darwin mistakenly
believed that giraffe
neck length was an
example of natural
selection
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some baby giraffes are born with slightly
longer necks
there is limited food, so longer-necked
giraffes get more food and survive better
over time the population would consist of
longer-necked giraffes
but Darwin was WRONG

giraffes spend more time eating low
leaves, not high leaves
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bending down to get a drink is awkward
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Why do giraffes need long necks?
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males fighting males
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this is an example
of sexual selection
Homologous vs. Analogous vs. Vestigial
Features
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homologous structures:
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similar strucures doing very different functions
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analogous structures:
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different structures doing very similar
functions
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vestigial structures:
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structures with no function in one organism,
but have a function in similar organisms
Macroevolution vs. Microevolution
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Macroevolution
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large scale evolutionary change significant
enough to warrant the classification of groups
or lineages into distinct genera or even
higher-level taxa
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i.e. many species arising from one common
ancestor
takes a very long time (10,000’s to millions of
years)

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e.g. evolution of birds or mammals
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e.g. Darwin’s finches
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Microevolution:
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changes in gene (allele) frequencies and
phenotypic traits within populations and
species; can result in the formation of new
species
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i.e. change within a species
takes less time (10’s to 1000’s of years)
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e.g. antibiotic-resistance in bacteria