Natural Selection

November 9 & 10

Do Now• Grab one of our brandy-spankin’ new Trackers• Start working on today’s warm-up:

Do you know anyone who looks like their mom or dad? What feature(s) does that person share

with his or her parent?

New Class Procedures• Warm-up/Exit Ticket tracker• Class log– If you arrive late– If you leave class for any reason

• New class website: DrMooreScience.com

Grades are updated• Work is returned to you in your hanging file• You can (and SHOULD) make up any work that

scores less than 75% of its point value

Quiz • Phones must be AWAY until EVERYONE has

finished.• You must be seated.• No shouting.• Failure to follow these rules is an automatic 1-

hour detention!!!• If in doubt about the legality of an action, raise

your hand and ask Dr. Moore

ObjectiveBy the end of class, students will be able to:

• Explain how natural selection causes a population to evolve.

Do you know anyone who looks like their mom or dad? What feature(s) does that person share

with his or her parent?

Natural Selection• Darwin’s argument:

1. There is variety in a population2. More individuals are born than can survive3. The individuals that are best able to survive and

reproduce will have the most offspring4. Offspring resemble their parents

1. There is variation within a population

2. Not everybody survives

3. Those who are best able to survive produce the most offspring

4. Offspring resemble their parents

Over time, traits that help an organism survive and reproduce will become more common

Over time, traits that harm an organism will become less common

Real-life example: Rock Pocket Mice

Rock Pocket MiceYou will receive illustrations representing snapshots of the rock pocket mouse population at four different points in time.1. Count the number of light-colored and dark-colored mice

present at each location at each moment in time. Record your counts in the spaces provided at the top of each illustration.

2. Place the illustrations in what you think is the correct order from oldest to most recent. Indicate your order by circling the appropriate number under the illustration.

Rock Pocket Mice3. Explain how you decided which illustration represents the

most recent rock pocket mouse population and why you positioned the other in the sequence as you did.

Rock Pocket MiceSequence

Oldest Second oldest

Third oldest Most recent

Location A # of mice with light fur# of mice with dark fur

Location B # of mice with light fur# of mice with dark fur

Rock Pocket Mice

Rock Pocket Mice Questions

1. Explain why a rock pocket mouse’s color influences its overall fitness. Remember, fitness is defined by an organism’s ability to survive and produce offspring.

Rock Pocket Mice Questions

2. Explain the presence of dark-colored mice at location A. Why didn’t this phenotype become more common in the population?

Rock Pocket Mice Questions3. Write a scientific summary that describes changes in

the rock pocket mouse populations at location B. Your summary should include– A description of how the population has changed over time– An explanation of what caused the changes– A prediction that describes what the population will look

like 100 years in the future. Base your prediction on the trends in the data you have organized. You can assume environmental conditions do not change over the 100 years.

Rock Pocket Mice Questions

3. Use the data and what you have learned about evolution to explain how mutation is a random process, but natural selection is not random.

Two Steps to a New Trait!• The trait arises in the population!– Mutation– Random

• The trait spreads in the population!– Natural selection– Non-random

DNADNA is a code It gives instructions

for building proteinsThose proteins build you!

DNA & Darwin’s Postulates1. There is variety in a population2. More individuals are born than can survive3. The individuals that are best able to survive and

reproduce will have the most offspring4. Offspring resemble their parents

There is variation in a population

• Due to differences in DNA sequence

• Changes to DNA happen randomly and are called mutations.

DNADNA is a code It gives instructions

for building proteinsThose proteins build you!

Offspring resemble their parents• Your mom gives you half of her DNA and your

dad gives you half of his DNA

Exit ticket• The ancestors of polar bears had brown fur.

Using your knowledge of natural selection and genetic mutations, explain how polar bears have white fur.– How did white fur first appear in the population?– Why did white fur become more common?