Download 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: Describes evolution toward similar traits in unrelated species.
• Survival advantage to a particular 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
Evolutionary Arms Race Continued…
Antibiotic Resistance
Bad
Good
• 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
Species Can Become Extinct
• 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?
• 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
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
– Descendent species
usually adapted to
different (wide range of)
environments