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 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 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

fatherlands.

• Must be geographically isolated.

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

fatherland.

• Can occur with species occupying different habitats, but in the same range.

• 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 species.

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 and facing different environmental challenges sometimes evolve dissimilar characteristics.

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

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 of change.

• Theory favored by early evolutionists.

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.

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.– 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

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 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 a social group often at the expense of the individual.

• Example: worker bees in a hive

• Kin Selection– Individuals help kin

raise their young.