Transcript 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.
Divergent Evolution
red fox
kit fox
ancestor
• Defined: Describes evolution toward different
traits in closely related species.
– Cause: Different environments
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 Continued…
• Coevolution can occur in competitive relationships,
sometimes called an evolutionary arms race.
– Example: Crab vs. Snail & Bacteria vs. Humans
Extinction
• Defined: The elimination of a species from Earth.
• Mass Extinctions:
• Background Extinctions:
– Cause: Catastrophic events
– Cause: Local changes in environment
– Ice Age, Meteorites
– Forest fires, habitat destruction.
– Destroys many species at global level
– Affects a few species in a small area
– Very severe
– Less severe.
– Rare but much more intense
– Occur at roughly the same rate as
– At least 5 mass extinctions in
speciation
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
Gradualism
of the Horse
How Fast Does Evolution Occur?
To radiate = to s-p-r-e-a-d out
• 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
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?