Chapter 10Principles of Evolution

Early scientists proposed ideas about evolution. Evolution- is the change of a species over time where a descendant become different from their ancestors

Species- is a group of organisms that can reproduce and have fertile offspring.

– Linnaeus: classification system from kingdom to species

– Buffon: species shared ancestors rather than arising separately

– Erasmus Darwin: more-complex forms developed from less-complex forms

– Lamarck: environmental change leads to use or disuse of a structure

There were many important naturalists in the 18th century.

E. Darwin Lamarck

Theories of geologic change set the stage for Darwin’s theory.

• There were three theories of geologic change.

• Catastrophism- natural disasters such as floods and volcanic eruptions cause evolutionary changes in species or extinction

• Gradualism- slow change over a long period of time (gradual- slow)

• Uniformitarianism- states that geologic processes that shape the Earth are uniform through time (uniform- always stays the same)

• Charles Darwin – p. 290WHO? British naturalist

WHAT? 5 year voyage on the Beagle from England around the world

WHERE? South America (Galapagos Islands)

WHY? Study variation in life forms

Darwin Video

• http://my.hrw.com/content/hmof/science/high_school_sci/tx/gr9-12/hmd_bio_9780544073890_/dlo/biologyvideoclips

Darwin observed differences among island species.

• Variation is a difference in a physical trait.– Galápagos tortoises that live in areas with tall

plants have long necks and legs.– Galápagos finches that live in areas with

hard-shelled nuts have strong beaks.• An adaptation is a feature that allow an

organism to better survive in its environment.– Species are able to adapt to their

environment.

Darwin observed fossil and geologic

evidence supporting an ancient Earth. • Darwin found fossils of extinct animals that

resemble modern animals.• Darwin found fossil shells high up in the

Andes mountains

After his voyage, Darwin spent over 20 years conducting research on evolution

• Darwin noticed a lot of variation in domesticated plants and animals.

• Artificial selection is the process by which humans select traits through breeding.

ex) faster horses, better fruiting plantsneck feathers

crop

tail feathers

Theory of Natural Selection

• Natural selection is a mechanism by which individuals that have inherited beneficial adaptations produce more offspring on average than do other individuals. “survival of the fittest”

• Heritability is the ability of a trait to be passed down.

• There is a struggle for survival due to overpopulation and limited resources.

• Darwin proposed that adaptations arose over many generations.

Four main principals….

• 1. Variation- heritable differences• 2. Overproduction- having lots of offspring

increases chance that some will survive ex) fish and reptile eggs

• 3. Adaptations- allow individuals to survive better than other individuals , more successful

individual live longer and reproduce• 4. Decent with modifications- more individuals

will have more favorable traits in future generations

Interactive Natural Selection

• http://my.hrw.com/content/hmof/science/high_school_sci/tx/gr9-12/hmd_bio_9780544073890_/dlo/animatedbiology

Evidence of Evolution1. Fossil Records- Paleontology- the study

of fossils or extinct organisms

2. Geography

3. Developmental Similarities» Notochord» Dorsal nerve cord» Pharyngeal arches

• 4. Anatomy• Homologous structures- similar in structure but

different functions

• Analogous structures- similar function but are not similar in origin

» Ex) bat wing and insect wing

Human hand Bat wingMole foot

Structural patterns are clues to the history of a species.

• Vestigial structures are remnants of organs or structures that had a

function in an early ancestor.

Molecular and genetic evidence support fossil and anatomical evidence.

• Two closely-related organisms will have similar DNA sequences

Embryonic Evidence

Fossil Evidence

http://my.hrw.com/content/hmof/science/high_school_sci/tx/gr9-12/hmd_bio_9780544073890_/dlo/thatsamazing/ind

Genetic variation in a population increases the chance that some individuals will

survive.• Genetic variation is stored in a

population’s gene pool.– made up of all alleles in a population– allele combinations form when organisms

have offspring

Sexual selection occurs when certain traits

increase mating success. • Sexual selection occurs due to higher cost

of reproduction for females.– males produce many sperm continuously– females are more limited in potential offspring

each cycle

• There are two types of sexual selection.– intrasexual selection: competition among

males– intersexual selection: males display certain

traits to females

Geographic barriers can cause isolation.

– called geographic isolation– physical barriers divide population

• Temporal barriers can cause isolation.– called temporal isolation– timing of reproductive periods

prevents mating

Evolution from natural selection isn’t random

• Convergent evolution describes evolution toward similar traits in unrelated species.

Divergent evolution describes evolution toward different traits in closely related species

How do convergent and divergent evolution illustrate the directional nature of natural selection?

Species can become extinct

Extinction is the elimination of a species from Earth.

– occurs at roughly the same rate as speciation

– usually affects a few species in a small area

– caused by local changes in environment