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Evidence supporting theory of evolution
• Analogous structures– Structures similar in
form and function.
• Develop as a result of convergent evolution?
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Evidence supporting theory of evolution
• Life’s chemistry– Organisms are made of molecules and
studying the molecules can help us understand possible relationships.
– Example: Proteins• Made of amino acids bonded together.
– Similar to a strand of pearls.
• More closely related two organisms are, the more closely their proteins resemble each other.
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Speciation
• Speciation: species giving rise to new species.– Some segment of original population must be
isolated from the rest.• Reproductive isolation is an essential ingredient.
• Occurs via two mechanisms:– Allopatric Speciation– Sympatric Speciation
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Allopatric speciation
• Definition: Speciation that occurs between isolated populations.– Originated in different
fatherlands.
• Must be geographically isolated.
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Allopatric speciation
• To reach and colonize new area, must realize three opportunities:– Geographic – Physiological– Ecological
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Sympatric speciation
• Definition: Speciation among populations whose ranges overlap. – Occur in same
fatherland.
• Can occur with species occupying different habitats, but in the same range.
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• Both types of speciation can be occurring at the same time.– Initially population is
geographically isolated.– If geographic barrier is
removed, populations overlap.
– Could still be isolated by differences in preferred habitat, courtship displays, breeding season, preferred.
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• If not isolated by differences, then two populations will merge into one species.
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Patterns in Evolution
• Convergent evolution– Unrelated species living in similar environments and
facing similar environmental challenges sometimes evolve similar characteristics.
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Patterns in Evolution
• Divergent evolution– Closely related species living in different
environments and facing different environmental challenges sometimes evolve dissimilar characteristics.
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Patterns in Evolution
• Adaptive radiation– Sometimes, several
species will evolve from a single, ancestral species.
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Patterns in Evolution
• Coevolution– Evolution of one species affects the evolution of
another species.• As predators evolve, prey evolves. As prey evolves,
predators evolve.
– Example: Cheetahs feed on Thompson’s gazelles• As the speed of one population of cheetahs improves so
does the speed of the Thompson’s gazelles .
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Patterns in Evolution
• Gradualism– Evolution may occur
as a slow, gradual process of change.
• Theory favored by early evolutionists.
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Patterns in Evolution
• Punctuated equilibrium– Evolution may proceed with
long periods of relatively little change (stasis) punctuated with short periods of intense change.
– Examples: House flies, trilobites, antibiotic-resistant bacteria.
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Evolution does not always occur
• Natural selection can only work on existing variation.
• Variation cannot be created on demand.
• Some species lack range of variation to support evolution.
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Results of evolution
• Everywhere we look on the Earth, you can find organisms.– Scientists have described 1.5 millions species
• Still many species yet to be described.
– Predictions indicate there may be 10-100 times as many species as those already described.
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Darwin’s Theory Debated
• Three main criticisms:– Darwin lacked direct evidence for natural
selection.• Indirect evidence was unconvincing
– Darwin could not explain the source of variation in a population and inheritance of variation.
• Answered by an understanding of genetics
– What is the rate at which organisms evolve?• Slow and continuous or jerky and discontinuous?
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Darwin recognizes three special cases of natural selection
• Sexual selection explained flamboyant appearance amongst birds.– Sexual selection: female birds choose mates and are attracted
to males with extreme features. – Females breed with them and extreme features passed to
offspring.
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Darwin recognizes three special cases of natural selection
• Altruism– Individual behavior
benefits a social group often at the expense of the individual.
• Example: worker bees in a hive
• Kin Selection– Individuals help kin
raise their young.