WHAT CAUSES WHAT CAUSES EVOLUTION TO OCCUR?EVOLUTION TO OCCUR?

DARWIN’S MECHANISM:

THE THEORY OF

NATURAL SELECTION

NATURAL SELECTIONNATURAL SELECTION• DEFINITION:

– the process by which organisms that are better suited to an environment survive and reproduce in greater number than those less suited.

• What causes natural selection?• Environmental Change

• “Survival of the Fittest”• (But what is fit????)

• Categorized into 5 Steps

STEP 1: Overproduction

• All species over reproduce creating a population with many variations.

STEP 2: Inherited Variation

VARIATIONS IN BIRD COLOR:• Most birds are born with traits (genes) for being blue-

green in color.• Occasionally some birds are born with traits that make

them more green. • Occasionally some birds are born with traits that make

them more blue.

Variations within a population come from mutations & random mating.

MUTATIONS: Changes in an organisms DNA or genes

RANDOM MATING: mixing of genes through reproduction

A change in the gene for feather color creates different looking variations of a birds population.

STEP 3: Struggle to Survive

Organisms compete for resources such as food, shelter, and mates. Those better suited to meeting these needs will survive.

The birds face the challenge of blending in to survive.

STEP 3: Struggle to Survive

Not all members of the species will survive this competition. Only some will survive and have the opportunity to pass on their successful genes.

Since blue-green birds stand out more in the habitat than green birds, more blue-green birds are eaten

Ugh!, so full…

EEP!

STEP 4: Successful Reproduction

Successful traits are passed to the next generation.Now, more members of the population are being

born with the successful variation than those with the less suited trait.

Now more green chicks than blue/ blue-green are being born.

STEP 5: Adaptation of the Species (Not included in the textbook)

Adaptation – process by which a species becomes better suited to its environment.

?

Hee, hee…

NATURAL SELECTION EXAMPLES

• Giraffe’s long neck

• Peppered Moth

• Ivory tusks of African elephant (textbook pg 122)

NATURAL SELECTION EXAMPLES

Antibiotics vs. Bacteria

Salmonella (bacteria that causes food poisoning)

vs

Salmonycin antibiotic (fights against Salmonella bacteria)

SPECIATION: Steps to a new species

SPECIES: a group of organisms that can interbreed and produce fertile offspring.

Steps to a NEW SPECIES1. Separation: part of a population becomes isolated from the rest.

• What could cause separation?

2. Adaptation: Natural selection improves the fit between species & environment. Populations diverge.

3. Division: Enough differences create a NEW SPECIES.

DIVERGENCE: the accumulation of differences between populations or species

Are these examples of species?

Example of Speciation:

Darwin’s Finches

(See page 124 in textbook or article)

At what pace does evolution occur?

GRADUALISM: states that evolution occurs slowly over time and includes many transitions

PUNCTUATED EQUILIBRIUM: states that evolution occurs in short bursts followed by long periods of stasis (no evolving)

Discussion Questions

• According to Natural Selection, explain why human overpopulation exists?

• Are humans evolving?