Download These are the events that cause evolution of a population:

These are the events that cause evolution
of a population:
• Mutations
• Non-random mating (artificial selection-like the roan cattle
problem)
• Migration (“gene flow”- genes moving into or out of the
population)
• Genetic drift:
– Bottleneck effect* (see next slide)
– Founder effect* (see the slide after that)
• The population is small (forces inbreeding)
• Natural selection** the only process that can result in
adaptive evolution
Does natural selection increase genetic diversity
of decrease it?
(Think about what you saw in “Toothpickfish”)
The Founder Effect: an example
of genetic drift
The genes that are in splinter populations are there by
chance; no selection takes place.
Bottleneck Effect: another example of genetic drift
(Is natural selection occurring here?)
Three types of end results of natural selection on a population…
Natural selection
helps to explain
how
a single species
changes over time…
But how do we get new ones?
And what is a species anyway?
A species are
members of a population that
can mate and produce fertile offspring.
Donkeys are a species because males
can mate with females and produce fertile little donkeys.
Horses are a species because males
can mate with females and produce fertile little horses.
Mules (a cross between a donkey and a horse) are NOT a species
because while males may try and mate with females, no offspring are
produced.
Making new
species is
called
speciation…
It begins with barriers to
reproduction…
Sometimes the barrier is
a geographic feature…
like a river, canyon,
mountain, or an island
This is an example of
geographic (or habitat)
isolation.
These are the events that cause evolution
of a population:
• Mutations
• Non-random mating (artificial selection-like the roan cattle
problem)
• Migration (“gene flow”- genes moving into or out of the
population)
• Genetic drift:
– Bottleneck effect* (see next slide)
– Founder effect* (see the slide after that)
• The population is small
• Natural selection** the only process that can result in
adaptive evolution
Making new
species is
called
speciation…
It begins with barriers to
reproduction…
Sometimes the barrier is
a geographic feature…
This is an example of
geographic (or habitat
isolation)
Sometimes enough
changes have taken
place between two
populations so that
the parts don’t fit to
enable
reproduction!
That’s called
mechanical
isolation.
Sometimes the barrier is a
behavioral one…
This is when courtship
rituals are not understood
between species.
Would the birds in this
picture understand the
meaning of the flashing
of a firefly lantern?
This is an example of
behavioral isolation.
Sometimes it is the
breeding season that
keeps two groups from
interbreeding.
This is called seasonal
(or temporal) isolation.
How fast can speciation take place?
In some cases
gradually ..
In other cases we get huge
changes (punctuated!) in a
short period of time
Stop Here!
Congratulations!
You survived Honors Biology!!!
Good luck on your final exams!
…Mrs. H