11.6 Patterns in Evolution

Patterns in Evolution

11.6 Patterns in Evolution

KEY CONCEPT Evolution occurs in patterns.•Evolution through natural selection is not random. o Natural selection can have direction.o The effects of natural selection add up over time.

11.6 Patterns in Evolution

Convergent evolution describes evolution toward similar traits in unrelated species. •Survival advantage to a particular

environment •Ex: Tuna (fish) and dolphins (mammals)

•Unrelated species with a similar environment (ocean)•Faced similar evolutionary pressures

11.6 Patterns in Evolution

Divergent evolution describes evolution toward different traits in closely related species.

ancestor

red foxkit fox

Cause: Different environments

11.6 Patterns in Evolution

Species can shape each other over time.

• Two or more species can evolve together in response to changes in eachother through coevolution.– evolutionary paths become connected– species evolve in response to changes in each other

Hummingbirds: Beak shape depends on flower shape

11.6 Patterns in Evolution

• Coevolution can occur in beneficial relationships.

• both species receive benefits from the other as a result of adaptations.

11.6 Patterns in Evolution

• Coevolution can occur in competitive relationships, sometimes called evolutionary arms race.

11.6 Patterns in Evolution

• Antibiotics: chemicals designed to kill bacteria– Produced by other

microorganisms to fight bacteria

• Antibiotic Resistance: Bacteria are adapting to the use of antibiotics– Overuse & misuse speeds

up the process– Importance: Bacteria

infections are becoming harder to treat

Fungus

Bacteria

11.6 Patterns in EvolutionAntibiotic Resistance

GoodBad

11.6 Patterns in Evolution

11.6 Patterns in Evolution

Species can become extinct.

• Extinction is the elimination of a species from Earth.• Background extinctions occur continuously at a very low

rate.

– occur at roughly the same rate as speciation

– usually affects a few species in a small area

– caused by local changes in environment

11.6 Patterns in Evolution

• Mass extinctions are rare but much more intense.

– destroy many species at global level– thought to be caused by catastrophic events (i.e. ice age)

– at least five mass extinctions in last 600 million years

11.6 Patterns in EvolutionHow Fast Does Evolution Occur?

• No exact time frame• Gradualism: slow & steady change of 1 species into another

– Small changes continually build• Punctuated Equilibrium: Rapid periods of evolution

– Due to sudden environment change– Ex: Mammal diversity exploded after dinosaur extinction

• Examples of both models exist

11.6 Patterns in Evolution

Gradualism of the Horse

11.6 Patterns in Evolution

• Many species evolve from one species during adaptive radiation.

– ancestral species diversifies into many descendent species

– descendent speciesusually adapted towide range ofenvironments