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