Patterns in Evolution

Key concept : Evolution occurs in patterns• Evolution through natural selection is not random.• Natural selection can have direction.• The effects of natural selection add up over time.

Convergent Evolution

Defined: evolution toward similar traits in unrelated species due to a similar environment.

• Ex: Tuna (fish) and dolphins (mammals). They are an unrelated species living in a similar environment, the ocean.• Faced similar evolutionary pressures.

• Defined: Describes evolution toward different traits in closely related species.– Cause: Different environments

ancestor

red fox kit fox

Divergent Evolution

Coevolution

• Defined: Two or more species evolve in response to changes in each other– Evolutionary paths become connected– Both species receive benefits from the other as a result of adaptations.

• Ex: Plants and Insects– Plants: provide insects with nectar– Insect: transfers pollen from one plant to another

• Coevolution can occur in competitive relationships, sometimes called an evolutionary arms race.– Example: Crab vs. Snail & Bacteria vs. Humans

Coevolution Continued…

GoodBad

• 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

Evolutionary Arms Race Continued… Antibiotic Resistance

Species Can Become Extinct • Defined: The elimination of a species from Earth.

• Background Extinctions:– Cause: Local changes in environment

– Forest fires, habitat destruction.– Affects a few species in a small area

– Less severe.– Occur at roughly the same rate as

speciation

• Mass Extinctions:– Cause: Catastrophic events

– Ice Age, Meteorites– Destroys many species at global level

– Very severe– Rare but much more intense

– At least 5 mass extinctions in last 600 million years

How Fast Does Evolution Occur?

• Gradualism: Slow & steady change of

1 species into another– Small changes continually

build over time

Punctuated Equilibrium: Long periods of little change are interrupted by shorter periods of rapid change.– Due to sudden environment change

– Ex: Mammal diversity exploded after dinosaur extinction

No exact time frame

Gradualism of the Horse

• Adaptive radiation: A process of evolution where one species can split into a number of different species.– Ancestral species diversifies into many descendent

species– Each adapted to a different environment• Ex: Mammals

How Fast Does Evolution Occur?To radiate = to s-p-r-e-a-d out

Review

• How is convergent and divergent evolution different?• What is thought to bring different organisms such as fish and dolphins to have

evolved a similar body plan?• What is coevolution?• What does a flower gain from a close relationship with a hummingbird?• What does the hummingbird gain?• How is gradualism and punctuated equilibrium different?