Download 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