Called “one long

argument” for

evolution

Hundreds of

thousands of

observations

Detailed, testable

theory

No mechanism for HOW

variation is passed from

parent to offspring

Modern synthesis:

combination of Mendel’s

and Darwin’s ideas

Comparing fossils

presents a pattern of

gradual change

Darwin found gaps in

the fossil record

Scenario 1: Leaves towards the bottom of trees are disappearing. Some giraffes can reach leaves higher up, while others’ necks are not long enough?

Which giraffes will thrive? Which giraffes will die out?

What will future generations look like?

Scenario 2: A certain species of rabbits in a dense forest come in brown and white fur colors. Hawks, soaring overhead, often eat the rabbits.

Which rabbits will be easier to spot?

Which color trait will more likely be passed on to future generations?

Individuals that display an “extreme” trait are selected for. Other individuals are selected against.

Population shifts toward this trait, away from the opposite.

Scenario 3: Lizards

range in size from tiny

to very large. Small

lizards generally run

very slowly while

large lizards are

usually the easiest for

predators to see.

What size lizard

stands the best

chance of survival?

Scenario 4: Human babies of very low birth weight are often more prone to disease. Babies of very large weights are difficult for mothers to safely deliver.

What size babies stand the best chance of survival?

Individuals that display an average trait are selected for.

Individuals that display extreme traits are selected

against.

Population shifts towards the average trait, and those

with extreme forms die off.

Scenario 5: Limpets are marine animals that attach to

rocks. Their color varies from pure white to dark brown.

White-shelled that are on rocks covered with goose

barnacles (also white) are at an advantage. On bare,

dark-colored rocks, brown limpets are at an advantage.

What “advantage” is being referred to above?

If you were a dark limpet,

where would you live?

A white limpet?

What color would have the

hardest time surviving?

Individuals that display either extreme are selected for. “Average” individuals are selected against.

Population shifts towards away from the average trait, towards BOTH extremes.

Design three example situations (1 paragraph each) representing the three types of selection we covered. Include the following:

1. Description of the animals involved and their traits

2. How is nature selecting for/against certain animals

3. Which trait will be come more common/less common and why?

4. Name the type of selection.

1) A group of crabs live on

a sandy beach. The

crabs range in color from

very light tan to dark

brown.

2) Seagulls, flying

overhead, eat the crabs.

They can more easily

see the dark crabs, since

the lighter ones blend in

with the color of the

sand.

3) Because the seagulls

more easily eat the dark

crabs, the lighter ones will

more likely survive and

reproduce, passing that

trait onto their offspring.

4) This is called “directional

selection.

Change in the allele frequency of a population

over time

Does chance

play a role?

Is evolution

predictable?

Populations will

remain at equilibrium

(and therefore not

evolve) unless some

outside factor affects

them

Equilibrium: frequency

of alleles is

unchanging

1. Natural Selection

2. Sexual Selection (mate choice)

3. Mutations

4. Gene flow (migration)

5. Genetic Drift and population bottlenecks

Movement of

individuals

(and alleles)

from one

population to

another

What are

some

barriers?

Change in allele frequency caused by chance events

More common in small populations

Can be beneficial, harmful, or neutral

Examples:• Founder Effect

• Population Bottleneck

Convergent evolution – similar environmental

pressures produce similar organisms

Coevolution – two organisms adapt to coexist

and support one another

Environmental factors

allow the development

of similar traits in very

different organisms

Ex: bats, beetles, birds

Species that live near

one another evolve to

benefit one another

Ex. sharks and fish

Ex. Yucca moth and

Yucca plant

Adaptive Radiation –

one species,

subjected to different

environmental

pressures, can evolve

into multiple species

…formation of a new

species

Often, one species can

branch from another

Extinction: the death of all

members of a single

species

Gradualism – tiny changes

become large-scale changes

over a long period of time

Punctuated Equilibrium –

sudden environmental

changes lead to new species

developing “quickly”

Morphological Concept: uses similarities

(physical and physiological) between

organisms

Biological Concept: group of organisms

that can breed and have fertile offspring

Geographic Isolation (Allopatric speciation)

Reproductive Isolation (Sympatric

speciation)