1. The ancestor giraffes had short necks.

2. The ancestor giraffes lengthened their necks by stretching to reach leaves.

3. The longer neck was passed on to offspring.

Whose theory of evolution is this?

Lamarck’s

Lamarck’s Hypothesis – Not Supported

• According to Lamarck’s hypothesis, organisms are striving for perfection.– Organisms can change their features to be perfectly suited

for their environment.

Does this look like a “perfect” organism to you?

Winter Flounder

Darwin’s Hypothesis – Well Supported

• According to Darwin’s hypothesis, organisms evolved by a process called natural selection.

What is natural selection?

Natural SelectionWhat is natural selection & how does it drive evolution?

What do you think is about to happen?

Natural Selection

• The process by which organisms who are better adapted to their environment will survive & reproduce

Some giraffes have long necks, but some giraffes have short

necks.

Which giraffes are probably better adapted for their environment?

The taller giraffes are more likely to survive & pass down their

genes to offspring.

Natural Selection – “Survival of the Fittest”

• Fitness: ability to survive & reproduce– High fitness means best adapted, not necessarily the

strongest.

Some beavers have large, strong teeth, but some beavers have

small, weak teeth.

Which beavers probably have the higher fitness?

The beavers with strong teeth are more likely to survive & pass

down their genes to offspring.

How does natural selection cause evolution?

Variation Within a Species

• Different individuals within a species have differences in their morphology & physiology.– Morphology: the form or shape of an organism– Physiology: the mechanical, physical, & biochemical

functions of living organisms

Morphology Physiology

Morphology – some of us are tall, while some

of us are short.

Physiology – some of us have a fast metabolism, while some of

us have a slow metabolism.

Morphology – some cats have long legs, but some cats have short legs.

Physiology – some cats can digest cow milk, but some cats can’t.

These differences change the ability of an organism to survive & reproduce (fitness).

• Some peppered moths are black & some are white.

• This variation allows some individuals to survive better than others.

• The moths that survive will reproduce & pass down beneficial traits.

Which moths have the higher fitness?

The black moths have a higher fitness than the white moths. They will survive & pass

on the black gene to offspring.

Adaptation

• Any inherited characteristic that increases an organism’s chance of survival & ability to reproduce– Increases fitness

Camels store fat in their humps to help them survive long

periods without food/water.

This is an adaptation that gets passed down from parent to

offspring.

A mouse has learned how to avoid mousetraps, increasing its chances of survival.

Is this an adaptation?

NO!

• Learned behaviors are NOT adaptations, because they’re not carried in genes, so they don’t get passed on to offspring.

• An adaptation is a trait that is coded for in genes, allowing it to be passed from parent to offspring.

Fitness & Adaptations

• Those individuals that have a higher fitness will pass on their morphological & physiological differences to their offspring.

Which mouse has the higher fitness?

The tan mouse blends in better, & therefore will survive better.

The tan mouse is more likely to reproduce & pass down the tan gene to

offspring.

Selective Pressures

• Over time, populations change based on the selective pressures of the environment.

• Selective Pressure: any factor that makes it hard for some organisms to continue surviving, & rewards any advantage that some organisms may have been born with

The selective pressure in an environment is what determines which organisms have a high fitness & which

ones have a low fitness.

Selective pressures drive populations to evolve.

Selective Pressures

• Climate Changes• Food Supply Changes• Predators• Sexual Selection

What type of selective pressure do you think affects this moth population?

Predators make it difficult for white moths to survive, giving them a lower fitness.

The black moths have the advantage, so they will contribute genes to the next generation.

Antibiotic Resistance

What’s the selective pressure driving this population to evolve?

Large ground finches use their large beaks to open seeds.

• Let’s say that the area has had an ideal amount of rainfall, so the plants are able to grow much larger.

• Since the plants are larger, the seeds are also much bigger.

• Now, only the finches with the biggest beaks can eat.

• The finches with smaller beaks don’t eat, so they don’t survive & reproduce.

• The finches with large beaks survive & pass on their “good genes” to the next generation.

What do you think the beak sizes will look like in the next generation?

The next generation of finches will probably have larger beaks – that is evolution by NS!

The Main Ideas of Natural Selection

• Organisms produce more offspring than can possibly survive.– Those that do not survive do not reproduce, & therefore do

not pass down their genes.

• Each organism has different advantages & disadvantages in the struggle for existence.

• Individuals best suited for their environment survive & reproduce most successfully.

The Main Ideas of Natural Selection

• “Survival of the Fittest”– Adaptations are inherited, NOT learned!– Adaptations may be an advantage in 1 environment, but a

disadvantage in another.

• Natural selection only acts on heritable traits.

A mouse that has learned how to avoid mousetraps does not pass that

down to its offspring in its genes.This is not an adaptation.

• Peppered moths in the industrial revolution

• http://www.utdanacenter.org/texteams/downloads/scienceresources/pradeep_fla.swf