Natural Selection

4.1.2 OUTLINE THE MECHANISM OF NATURAL SELECTION AS A POSSIBLE DRIVING FORCE FOR SPECIATION.

http://evolution.berkeley.edu/evolibrary/article/evo_25

What is evolution? What does it mean to you?Do you think it happens?Evidence? (for or against)

Evolution are the changes in the gene pool of a population over time.

Natural selection process by which individuals that are better suited to their environment survive and reproduce most successfully.

Adaptation is an inherited characteristic that increases an organism’s chance of survival.

DEFINITIONS:

Darwin and Evolution

1809-1882

Isabela

Darwin

Wolf

Pinta

Marchena Genovesa

Fernandia

SantiagoBartolomé

RåbidaPin zon

SeymourBaltra

Santa Cruz

Santa Fe

Tortuga

Española

San Cristobal

Floreana

EQUATOR

GalåpagosIslands

Sailed around world 1831-1836

Through his travels he found that species diversity was much greater than previously known.

Each island had its own type of tortoises and birds

Land Iguana

Marine Iguana

His observations led to the development of the theory of evolution.

What is a Theory? A well tested idea that explains an observed phenomena Supported by multiple sources of evidence

Darwin’s Postulates

Populations have natural VariationOverproduction of offspring.Struggle for existence.Unequal survival and reproduction rates. (Those with traits more likely to help them survive will pass traits to their offspring)

What is a species?A group of individual organisms that are capable of reproducing and produce viable offspring. When organisms can no longer reproduce or do not produce viable offspring then they are no longer the same species.

FOUNDER SPECIES

insect and nectar eatersfruit and seed eaters

KAUAI AKIALAOA

AMAKIHI

IIWI

APAPANE

KONA FINCH extinct

LAYSAN FINCH

AKIAPOLAAU

MAUI PARROTBILL

Based on his observations, Darwin proposed that EVOLUTION occurs

by NATURAL SELECTION.

Population of organisms

Limited resources leads to a struggle for survival

between offspring.

Overproduction of offspring

Survivors reproduce more successfully.

Mutations & Sexual reproduction

produces variations among offspring.

Population changes over time.

• Populations evolve by becoming genetically different

• Genetic variations• First step in biological evolution• Occurs through mutations in

reproductive cells• Mutations in other cells can

happen , but only reproductive cell mutations are passed on

• Sometimes a mutation can result in a new genetic trait that gives it a better chance to survive, sometimes not.

The Genetic Makeup of a Population Can Change

Individuals in Populations with Beneficial Genetic Traits Can Leave More Offspring

• Natural selection: acts on individuals• Second step in biological evolution• Adaptation may lead to differential reproduction• Genetic resistance in bacteria, cockroaches

• When environmental conditions change, populations• Adapt• Migrate• Become extinct

A group of bacteria, including genetically resistant ones, areexposed to an antibiotic

Normal bacterium

Resistant bacterium

Most of the normal bacteria die

The genetically resistant bacteriastart multiplying

Eventually the resistant strainreplaces the strain affected bythe antibiotic

Evidence Supporting Evolution

Fossil Record

Evidence Supporting Evolution

Homologous Structures

Evidence Supporting Evolution

Vestigial Structures

Evidence Supporting Evolution

Embryo Development

Opposing Theory at the TimeLamark: Theory of Acquired Traits

Lamark believed that organisms acquired traits by using their bodies in new ways

These new characteristics were passed to offspring

Why was Lamark’s theory refuted???

Can a fish species willfully grow limbs and fingers if they are needed to crawl out of the water onto dry land?

Origin of Species Darwin published his book The Origin of Species in 1859

His findings are still supported today by further evidence and the scientific community.

Activity:

http://phet.colorado.edu/en/simulation/natural-selection (requires shockwave)http://sepuplhs.org/high/sgi/teachers/evolution_act11_sim.html http://biologyinmotion.com/evol/http://www.techapps.net/interactives/pepperMoths.swf (requires flash)http://www.sciencechannel.com/games-and-interactives/charles-darwin-game.htm

• Choose two online natural selection simulations. • Work through the simulation and discuss the

strengths and weaknesses of the simulation with regard to modeling natural selection.

• Which simulation do you believe does a better job modeling natural selection? Justify your answer.

• In your own words, explain how a new species forms.