The story of the peppered moth:

1850:1850: mostly speckled; a few dark

2000:2000: mostly speckled; a few dark

1900:1900: mostly dark; a few speckled

The story of the bacteria:

• 1st round of antibiotics:

most bacteria diemost bacteria die

• 2nd round of

same antibiotic: some diesome die

• 3rd round of

same antibiotic:

very few dievery few die

What do these two stories have in common?

Per. _

If all offspring of two parent fish survive and If all offspring of two parent fish survive and reproduce, how many fish will there be after 4 generations?reproduce, how many fish will there be after 4 generations?

WHAT DO WE OBSERVE ABOUT WHAT DO WE OBSERVE ABOUT POPULATIONS OF ORGANISMS?POPULATIONS OF ORGANISMS?WHAT DO WE OBSERVE ABOUT WHAT DO WE OBSERVE ABOUT POPULATIONS OF ORGANISMS?POPULATIONS OF ORGANISMS?

Another example:Another example: How many flies would there be by the end of one summer if all How many flies would there be by the end of one summer if all offspring of a mating pair survived and reproduced?offspring of a mating pair survived and reproduced?

What can be said about the What can be said about the potential of populations?potential of populations?

What can be said about the What can be said about the potential of populations?potential of populations?

Populations of organisms have the potential to grow exponentially.

Graph of exponential growth:Graph of exponential growth:

Is this what really happens?• Are we overrun by fish… or flies… or any

single species?• What really seems to happen? In other

words, what do we observe in real life?

A species of fishA species of fish

A species of grassA species of grass

Biomassof

population

YeastYeastSheepSheep

Paramecium (a protist)Paramecium (a protist)

What is the pattern?

How would you describewhat populations really seem to do?

OBSERVATION #2:OBSERVATION #2:OBSERVATION #2:OBSERVATION #2:

Populations of organisms tend to stay relatively stable in size.

OBSERVATION #2:OBSERVATION #2:OBSERVATION #2:OBSERVATION #2:

Populations of organisms tend to stay relatively stable in size.

1. Even student #’s are DEER, odds are RESOURCES .2. Signs for resources: FOODFOOD = both hands over belly,

WATERWATER = both hands over mouth, SHELTERSHELTER = make a tent over head.

3. Groups stand with backs to each other. Everyone picks a resource by making the appropriate sign. You must keep displaying your sign the whole time!

4. On teacher’s signal turn and face each other. DEER must find someone showing the same resource on the other side.

5. Each deer can only claim one resource.6. No changing once you turn around!7. If a deer finds a resource it can “reproduce”. The

resource it caught becomes a deer for the next round.8. Resources not claimed stay a resource.9. Deer not able to find their resource die and become a

resource for the next round.

““OH DEER”OH DEER”

1. Was it always easy to be a deer in the game? Why or why not?

2. When resources were limited, what did it feel like to be a deer?

DISCUSSION:

INFERENCE #1INFERENCE #1INFERENCE #1INFERENCE #1• Within populations of organisms

there is a struggle to survive.

What do we observe when we compare individuals in a population?

OBSERVATION #4OBSERVATION #4There is variation among organisms in

a population. Variation naturally exists.

Wormeaters

What is going to happen to:

…the wormeater with the disadvantageous variation?

…the wormeater that got the most food?

Per.

OBSERVATION:OBSERVATION:

Individuals with advantageous

variations have a better chance of

surviving than those with less advantageous variations.

OBSERVATION:OBSERVATION:Survival allows reproduction

When the surviving wormeaters reproduce what kind of beaks will their

offspring most likely have?OBSERVATION:OBSERVATION:

Many variations are inherited (in other words, offspring tend to resemble their parents).

What do you predict would happen to the ## of individuals with the advantageousadvantageous

variation in the next generation?

conclusion:conclusion:The # of individuals with advantageous variations will increase in each new generation. The # with disadvantageous traits will decrease.

What about the # of individuals with the disadvantageousdisadvantageous variations?

What do you predict will happen to a species over

many generations?PREDICTION:PREDICTION:

Over many generations the species changes, i.e. EVOLUTION occurs.

OVERVIEW of the MODEL

OBSERVATION #1Populations have potential to grow

exponentially.

OBSERVATION #2Population sizesremain relativelystable over time.

OBSERVATION #3Stable population sizes are due to limited resources.

INFERENCE #1Within populationsthere is a struggleto survive.

OBSERVATION #4Within populationsthere is variation.

OBSERVATION #5Some variations

provide a survival advantage.

OBSERVATION #6Individuals who

survive can reproduce.

OBSERVATION #7Many variations

are heritable.

INFERENCE #2# individuals with

advantageoustraits increases in each generation.

INFERENCE #3Over many

generations, species change. EVOLUTION

occurs!