Evolution: changes through time


- Species accumulate difference


- Descendants differ from their ancestors

- New species arise from existing ones

Natural Selection

Remember natural selection is just a process that that can cause evolution

Principles of Natural Selection

• For natural selection to occur these must take place in a species
• There are 5 

1. Organisms produce more offspring than can survive

1. Organisms produce more offspring than can survive

2. Differences, variations, occur among individuals

3. Some variations are passed on to offspring

4. Some variations that are passed on are helpful. Helps organism survive

5. Over time, the offspring of individuals with the helpful variations make up more of a population and could become a separate species

Other Mechanisms of Evolution

• Genetic Drift
• Mutation
• Migration (Gene Flow)

Mutations

It not a common event (typical mutation rates are about one mutation in a million genes passed from generation to generation)


as a result, evolution through mutation is extremely slow.

Mutation is very important for evolution because, ultimately, mutation is the source of genetic variation. Other forms of evolution on cannot occur without genetic variation.

Genetic Drift

is change in allele frequency by random chance. Usually in Small populations

Migration (Gene Flow)

is change in allele frequency that occurs because individuals move among populations

Speciation can happen over a period time

lineage-splitting event that produces two or more separate species

Cause of this can be Geographic Isolation

Geographic Isolation

- Terrain can separate a population
- Over time population's genes differ
- If enough genes change between population then they will no longer be able to reproduce between the populations

Darwin's theory of evolution by natural selection emphasizes the differences among individuals of a species....variations & adaptations

1. Variation in Traits

• Populations will have differences in genes
• Example: Beetle population with different colors

2. Differential Reproduction -

some individuals survive and reproduce, some don’t

3. Heredity - Traits are passed down

4. Advantageous Traits are passed down more often

Eventually, all members of the population would exhibit that same advantageous trait

Types of Natural Selection

• Directional selection
• Stabilizing selection
• Disruptive selection

Directional Selection

natural selection favors one extreme of continuous variation. Over time, the favored extreme will become more common and the other extreme will be less common or lost.

Example: Oysters

If thicker-shelled oysters are more resistant to breakage than thinner-shelled oysters, crabs will be less able to prey upon them, and thicker-shelled oysters will be more likely to survive to reproduce.

Stabilizing

occurs when natural selection favors the intermediate states of continuous variation

Disruptive

occurs when natural selection favors both extremes of continuous variation

Evidence of Evolution

Evidence of Evolution

• Fossil Evidence
• Structural Evidence
• Genetic Evidence
• Embryological Evidence

Fossils

• Remains or imprints of once living organisms are FOSSILS
• Remains or imprints of once living organisms are FOSSILSFOUR different types of fossils (Cast, Mold, Trace, True Form)
• Remains or imprints of once living organisms are FOSSILS
• FOUR different types of fossils (Cast, Mold, Trace, True Form)

Fossils

• Most fossils will be found in SEDIMENTARY ROCK layers
• General rule is that the deeper a fossil is in the ground the older it is
• Called LAW OF SUPERPOSITION
• Or Relative Age Dating

How Fossils Form

• Commonly form when dead organism is covered with a layer of sediment or mud
• As more time passes more sediment is deposited on top of organism

Mold Fossils

• Created when a shell or other structure is buried in sediment and then dissolved by underground water
• Only the shape and surface markings of the organism are left

Cast Fossils

• Created if the hollow spaces of a mold are later filled with mineral matter

Trace Fossils

• Usually footprints
• Forms the same way as if you put your hand or foot in concrete before it dries

True Form Fossils

• Formed when the animals soft tissues or hard parts did not decay over the years because they are trapped in sap, ice, or tar.

Fossil Record

• Record of the fossils that have been discovered
• Organized by their ESTIMATED AGES (based on radiometric and relative dating) and PHYSICAL SIMILARITIES

Fossil Record

• Scientists use this info to hypothesize the RELATIONSHIPS between EXTINCT and LIVING organisms
• They look at GEOLOGICAL and STRUCTURAL similarities between different fossilized organisms

Fossil Record

• Gaps = Chunks of geological time for which a fossil has not been discovered
• As well as the transition between two groups of organisms

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