Keystone Review

Evolution

Misconception: “Evolution is ‘just’ a theory.”Response: Scientific

theories are explanations that are based on lines of evidence, enable valid predictions, and have been tested in many ways. In contrast, there is also a popular definition of theory—a “guess” or “hunch.” These conflicting definitions often cause unnecessary confusion about evolution.

Evolution by Natural Selection

• EVOLUTION is the THEORY of how organisms have changed over time.

• Charles Darwin did NOT make this up!– His theory is

accepted today

• NATURAL SELECTION is the MECHANISM by which Evolution takes place.– Natural selection

drives evolution

• It does not attempt to explain how life began.

Natural SelectionThe process whereby organisms better adapted to their

environment tend to survive and produce more offspring

Kettlewell – England – Peppered Moths

Allelic Frequency

Genetic Drift

• Evolution that is not caused by natural selection• Caused by RANDOM CHANCE!• Adaptations are not passed on because the

“best” organisms are not surviving, just the luckiest.

Genetic Drift—Bottleneck Effect

Genetic Drift—Founder Effect

Speciation—forming a new species

Speciation—forming a new species• Occurs when members of similar populations

no longer interbreed to produce fertile offspring within their natural environment.

Usually have two requirements1.Geographic Isolation2.Reproductive isolation

Geographic Isolation

Reproductive Isolation(and other isolating mechanisms)

Offspring Sterility

Habitat Isolation - Lizards

• Lizard on left prefers shade: tree dweller

• Lizard on right prefers sunlight: ground dweller or on the fence where it can sunbathe.

Mechanical Isolation

Mechanical Isolation• The flowers of black sage

and white sage are structurally different and are pollinated by different species of insects.

• In this example, each insect species pollinates flowers of only one of the sage species. Therefore, interbreeding does not occur.

Behavioral Isolation• Behavioral Isolation is when two populations,

because of facing differing sexual selection pressures, will acquire different mating rituals and behaviors.

• Some organisms within a population will not breed with another organism if it doesn’t have the same mating rituals.

Temporal Isolation• Temporal Isolation occurs when two organisms have different

breeding times. This is separation in time.• Flowers bloom at different times of year, and therefore will not cross

pollinate. In this way, two species can be reproductively isolated, yet live side-by-side.

Types of Evolution

• Divergent• Convergent

Divergent Evolution

Divergent Evolution

Convergent Evolution

Artificial Selection

Coevolution

Evidence for evolution--Fossils

Biogeography

Chapter 15Section 2 Evidence of Evolution

Hemoglobin Comparison

Biochemical

Chapter 17

Similarities in Amino Acid Sequences

Section 2 Systematics

Biochemical

Universal Genetic Code

Homologous Structures

• Forelimbs of vertebrates

Analogous Structures

Vestigial Structures

Evidence of Whale Evolution

Section 2 Evidence of EvolutionChapter 15

Embryology