1. 17-4 Patterns of Evolution
Macroevolution refers to large-scale evolutionary patterns and processes that occur over long periods of time.
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2. Patterns in Evolution
Evolution through natural selection is not random.
Natural selection can have direction.
The effects of natural selection add up over time.

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Macroevolution
Six important topics in macroevolution are:
extinction
divergent evolution
convergent evolution
coevolution
punctuated equilibrium
adaptive radiation
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Extinction
Extinction is the elimination of a species from the earth
More than 99% of all species that have ever lived are now extinct.
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5. Background Extinction
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

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Mass Extinction
Mass extinctions are rare but much more intense.
destroy many species at global level
thought to be caused by catastrophic events
at least five mass extinctions in last 600 million years
What effects have mass extinctions had on the history of life? Mass extinctions have:
provided ecological opportunities for organisms that survived
resulted in bursts of evolution that produced many new species
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Convergent Evolution
Convergent Evolution
Different organisms undergo adaptive radiation in different places or at different times but in similar environments.
Convergent evolution describes evolution toward similar traits in unrelated species.
Results in analogous structures.
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8. Divergent Evolution
Divergent evolution describes evolution toward different traits in closely related species.
How do convergent and divergent evolution illustrate the directional nature of natural selection?
ancestor
red fox
kit fox

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Coevolution
Coevolution
Sometimes organisms that are closely connected to one another by ecological interactions evolve together.
The process by which two species evolve in response to changes in each other over time is called coevolution.
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10. Benefits of Coevolution
Coevolution can occur in beneficial relationships.
Both species receive benefits from the other as a result of adaptations that each species has evolved over many generations

11. Evolutionary arms races
Both species respond to competitive pressure from the other through adaptations over many generations

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Adaptive Radiation
Adaptive Radiation
Adaptive radiation is the process by which a single species or a small group of species evolves into several different forms that live in different ways and adapt to a wide range of environments.
For example, in the adaptive radiation of Darwin's finches, more than a dozen species evolved from a single species.
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14. Punctuated Equilibrium
Punctuated equilibrium is a pattern of evolution in which long stable periods are interrupted by brief periods of more rapid change.
Biologists have considered two different explanations for the rate of evolution, as illustrated in these diagrams. Gradualism involves a slow, steady change in a particular line of descent. Punctuated equilibrium involves stable periods interrupted by rapid changes involving many different lines of descent.
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15. Gradualism (left) vs Punctuated equilibrium (right)
In contrast to the concept that life forms change slowly over time in response to their environment, punctuated equilibrium is a theory that those changes occur in spurts of time periodically.
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17-4
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17-4
Darwin's species of finches were very similar but different in beak size and feeding habits. This is an example of
convergent evolution.
coevolution.
adaptive radiation.
stabilizing selection.
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A slow steady change in a particular line of descent is called
coevolution.
gradualism.
punctuated equilibrium.
convergent evolution.
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17-4
Master control genes are called
hox genes.
developmental genes.
embryonic genes.
regulatory genes.
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Some evidence suggests that species do not change much over long periods of time and then undergo relatively short periods of rapid speciation. This kind of change is called
coevolution.
genetic equilibrium.
adaptive radiation.
punctuated equilibrium.
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17-4
Fossil evidence shows that mass extinctions
ended the existence of many species in a short period of time.
occurred mainly when the dinosaurs disappeared.
require an asteroid strike to occur.
caused convergent evolution among animals.
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