Evidence supporting theory of evolution Analogous structures Structures

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Evidence supporting theory of evolution • Analogous structures – Structures similar in form and

Evidence supporting theory of evolution • Analogous structures – Structures similar in form and function. • Develop as a result of convergent evolution?

Evidence supporting theory of evolution • Life’s chemistry – Organisms are made of molecules

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.

Speciation • Speciation: species giving rise to new species. – Some segment of original

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

Allopatric speciation • Definition: Speciation that occurs between isolated populations. – Originated in different

Allopatric speciation • Definition: Speciation that occurs between isolated populations. – Originated in different fatherlands. • Must be geographically isolated.

Allopatric speciation • To reach and colonize new area, must realize three opportunities: –

Allopatric speciation • To reach and colonize new area, must realize three opportunities: – Geographic – Physiological – Ecological

Sympatric speciation • Definition: Speciation among populations whose ranges overlap. – Occur in same

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.

 • Both types of speciation can be occurring at the same time. –

• 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.

 • If not isolated by differences, then two populations will merge into one

• If not isolated by differences, then two populations will merge into one species.

Patterns in Evolution • Convergent evolution – Unrelated species living in similar environments and

Patterns in Evolution • Convergent evolution – Unrelated species living in similar environments and facing similar environmental challenges sometimes evolve similar characteristics.

Patterns in Evolution • Divergent evolution – Closely related species living in different environments

Patterns in Evolution • Divergent evolution – Closely related species living in different environments and facing different environmental challenges sometimes evolve dissimilar characteristics.

Patterns in Evolution • Adaptive radiation – Sometimes, several species will evolve from a

Patterns in Evolution • Adaptive radiation – Sometimes, several species will evolve from a single, ancestral species.

Patterns in Evolution • Coevolution – Evolution of one species affects the evolution of

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.

Patterns in Evolution • Gradualism – Evolution may occur as a slow, gradual process

Patterns in Evolution • Gradualism – Evolution may occur as a slow, gradual process of change. • Theory favored by early evolutionists.

Patterns in Evolution • Punctuated equilibrium – Evolution may proceed with long periods of

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, antibioticresistant bacteria.

Evolution does not always occur • Natural selection can only work on existing variation.

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.

Results of evolution • Everywhere we look on the Earth, you can find organisms.

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.

Darwin’s Theory Debated • Three main criticisms: – Darwin lacked direct evidence for natural

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?

Darwin recognizes three special cases of natural selection • Sexual selection explained flamboyant appearance

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.

Darwin recognizes three special cases of natural selection • Altruism – Individual behavior benefits

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.