unit 10 natural selection

10.3 Theory of Natural Selection

KEY CONCEPT There were theories of biological and geologic change before Darwin.


Early scientists proposed ideas about evolution.

• Evolution is the biological change process by which descendants come to differ from their ancestors.

• A species is a group of organisms that can reproduce and have fertile offspring. Give an example of a species.

• What is an example of two animals that are similar, can breed, but the offspring are not fertile?


• There were many important naturalists in the 18th century.– Linnaeus: classification system from kingdom to species– Buffon: species shared ancestors rather than arising

separately– E. Darwin: more-complex forms developed from less-

complex forms– Lamarck: environmental change leads to use or disuse

of a structure


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

• There were three theories of geologic change in place before Darwin did his studying.– catastrophism

– gradualism– uniformitarianism


• Uniformitarianism is the prevailing theory of geologic change. How much time would it take to form layers of rock such as this?


KEY CONCEPT Darwin’s voyage provided insight on evolution.


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. Why would that be an advantage?

– Galápagos finches that live in areas with hard-shelled nuts have strong beaks. Why would that be an advantage?


• An adaptation is a feature that allows an organism to better survive in its environment.

– Species are able to adapt to their environment. Why is this important?

– Adaptations can lead to genetic change in a population.


• Darwin found fossils of extinct animals that resemble modern animals.

• Darwin found fossil shells high up in the Andes mountains.

Darwin observed fossil and geologic evidence supporting an ancient Earth.


• He saw land move from underwater to above sea level due to an earthquake.

• Darwin extended his observations to the evolution of organisms.

• We say this like it is a small thing but consider all the variety of studies that he had to consider…


Multiple disciplines had to be considered…

• Geologic time scale• Fossil evidence• Species diversity• Species dispersal• Pangea• Observations

• Now we can add radiometric dating and DNA evidence to the list.


What term describes the theory that natural disasters shaped Earth's landforms and caused species to become extinct?

A. Gradualism

B. Uniformitarianism

C. Catastrophism

D. Evolution



A. Gradualism


C. Catastrophism

D. Evolution

Correct Answer = C

What must be true of two individuals of the same species?

A. They can reproduce and have fertile offspring.

B. They must live in the same environment.

C. They can reproduce, but their offspring are not fertile.

D. They can pass acquired characteristics to their offspring.



A. Gradualism


C. Catastrophism

D. Evolution

Correct Answer = C

What must be true of two individuals of the same species?

A. They can reproduce and have fertile offspring.

B. They must live in the same environment.

C. They can reproduce, but their offspring are not fertile.

D. They can pass acquired characteristics to their offspring.

Correct Answer = A


Review

• Evolution is the process of change resulting in descendents that are different from their ancestors.

• A species is a group of organisms that can reproduce to form viable offspring.

• Variation is difference in a physical trait.• Adaptation is a feature that allows an organism to better

survive in its environment• Adaptations can lead to a genetic change in a population.• Fossil evidence and observation of adaptations led to

Darwin’s understanding of life’s evolution.


KEY CONCEPT Darwin proposed natural selection as a mechanism for evolution.


• Natural selection is a mechanism by which individuals that have inherited beneficial adaptations produce more offspring on average than do other individuals.

• Heritability is the ability of a trait to be passed down. Give an example of a trait that is heritable.

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

• Darwin proposed that adaptations arose over many generations due to the slight advantage given by variation of traits.


Several key insights led to Darwin’s idea for natural selection.

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

• Artificial selection is the process by which humans select traits through breeding. What are some animals we have selectively bred?

neck feathers

crop

tail feathers


• There are four main principles to natural selection.– variation

Natural selection explains how evolution can occur.

– overproduction– adaptation– descent with modification

VARIATIONOVERPRODUCTIONADAPTATION

• Fitness is the measure of survival ability and ability to produce more offspring.

DESCENT withMODIFICATION


• Natural selection can act only on traits that already exist. Why?

• Structures take on new functions in addition to their original function.

Natural selection acts on existing variation.

wrist bone

five digits

10.4 Evidence of Evolution

KEY CONCEPT Evidence of common ancestry among species comes from many sources.


Evidence for evolution in Darwin’s time came from several sources.

• Fossils provide evidence of evolution.• Fossils in older layers are more primitive than

those in the upper layers. If this were NOT true, what would we expect to find?


• The study of geography provides evidence of evolution.

– island species most closely resemble nearest mainland species. If geography did NOT provide evidence of evolution, what would you expect to see among birds in different parts of the world?

– populations can show variation from one island to another. If evolution were not continuing to happen, what would you expect to see among populations on neighboring islands?


• Embryology provides evidence of evolution.

Larva

Adult barnacleAdult crab

– identical larvae, different adult body forms– similar embryos, diverse organisms– If organisms were NOT related, what would you expect

when you compared their embryos?


• The study of anatomy provides evidence of evolution.

Human hand Bat wingMole foot

– Homologous structures are similar in structure but different in function.

– Homologous structures are evidence of a common ancestor. Why?


Human hand

Bat wing

Mole foot

Fly wing

– Analogous structures are not evidence of a common ancestor. Why?

• The study of anatomy provides evidence of evolution.

– Analogous structures have a similar function.


• Vestigial structures are remnants of organs or structures that had a function in an early ancestor.

• Ostrich wings are examples of vestigial structures. What is an example of a vestigial structure in humans?

Structural patterns are clues to the history of a species.


What adaptations did Darwin see in the tortoises of the Galapagos Islands?

A. Shape of beak

B. Length of neck and legs

C. Shape of head

D. Kind of shell



A. Shape of beak


C. Shape of head

D. Kind of shell

Correct Answer = B

What did the variations in the Galapagos finches seem to be well suited to?

B. The animals' size

B. The animals' age

C. The island the animals lived on

D. The animals' environment and diet



A. Shape of beak


C. Shape of head

D. Kind of shell

Correct Answer = B

What did the variations in the Galapagos finches seem to be well suited to?

B. The animals' size

B. The animals' age

C. The island the animals lived on

D. The animals' environment and diet

Correct Answer = D

Review

• Natural selection occurs when an adaptation that is a heritable trait makes survival more likely. When there is a struggle for survival, the trait is passed on to more offspring in a population until, over time, the adaptation is present in the general population.

• There are four principles of natural selection– Variation– Overproduction– Adaptation– Descent with modification

• Fitness is the measure of ability to survive and produce offspring that will survive.

Review

• Fossil evidence shows more simplistic organisms in lower, older, layers and more complex organisms in higher, more recent layers of rock

• Embryology shows evidence of evolution• Anatomy shows evidence of evolution

– Homologous structures – similar structure, different function. Suggests common ancestor

– Analogous structures – similar function. Does not suggest common ancestor

• Vestigial structures give hints to ancestry and history of species

unit 10 natural selection

Documents

fertile offspring

biological change process

theories of biological

geologic change

early scientists

key concept

group of organisms