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