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Evolution and Natural Selection

Continued

The gradual change in a species over

time.

Evolution is…

Things to keep in mind…

Populations, not individuals, evolve.

It’s all about the genes!

Occurs over a LONG period of time.

Evidences of Evolution

Fossil Record

Biochemical - DNAComparative Anatomy

Biogeography

Observable Events

How does evolution

occur?

Mechanisms of Evolution

Bottleneck EffectAn event that kills off

a large number of members of a species randomly by chance therefore reducing

the genetic diversity.

Bottleneck Effect

Genetic DriftThe alteration of

allelic frequencies by chance events.

Genetic Drift

MutationsRandom genetic

changes that occur in a populations

DNA.

Mutations Most mutations are bad

Some are advantageous

Gene FlowThe transfer of alleles from one population

to another population through immigration

or emigration of individuals.

Gene Flow

A mechanism for change in a population.

Natural Selection is…

Survival of the FittestOrganisms with favorable

genetic variation survive to pass on their genes

Types of Natural Selection

1.Stabilizing2.Directional3.Disruptive

Stabilizing Selection:When the average is favored over

either of the extremes in a population.

Stabilizing Selection:

Directional Selection:This happens when one of the “extremes” is favored in an environment over the other extreme or the old average.

Directional Selection:

Disruptive Selection:This situation happens when

either extreme is favored over the average.

Disruptive Selection:

How are new species made?

Speciation: the evolution of a new species

How are Species Made?Speciation is always caused by isolationTypes of isolation:

1. Geographic2. Reproductive

Types of Isolation1. Geographic

IsolationA single species can become two different species because they are isolated by mountains, rivers, canyons, etc.

Types of Isolation2. Reproductive Isolation

› Animals in different areas of the country may develop different actions and behaviors.

› These different behaviors can cause groups to separate from each other and become different species.

Types of Isolation2. Reproductive

IsolationOrganisms may develop different mating seasons which do not correspond to one another

Individuals die, species go extinct

As the environment changes, organisms must have variations that allow them to survive (adapt) to those changes or dieIf an entire population of a species cannot adapt, that species becomes extinct.

There have been at least 5 MASS extinctions during Earth’s history where a huge % of the living species were destroyed

At least one of these has been attributed to

meteor impact and its

consequences.