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Darwin and Natural Selection

Background: Students know Evolution is change over time

Essential Question: What was Darwin’s conclusion about his observations? (CIRCLE ans. )

Vocabulary: Highlight or underline the 5 facts of evolution

I. EvolutionA. variation is inherited, not acquired (Darwin):

Lamarck:

individuals have to stretch to reach leaves; figuring that a long neck is

better, they produce offspring with long necks

Darwin:

Some individuals happen to be born with a long neck; they can reach

food better, get stronger, produce more offspring --> trait will spread in the population

B. Descent with Modification

1. change is based on the interactions between populations & pressure from the environment

2. is a change over time in the genetic composition of a population

DO NOT COPYIn (1859) Darwin published the book: On the Origin of Species by Means of Natural Selection as a mechanism for evolution

Historical Process of ScienceDO NOT COPY The next

slidesAristotle:

-life-forms arranged on scale on increasing complexity (scala naturae)-he viewed species as unchanging

- His ideas were supported for a long time

Aristotle 384-322 B.C.

Until the 1700’s many scientists used the next two ideas to explain life on earth

Old Testament - Creationism:

Earth ~6000 years old; perfect species individually designed by God

Natural theology: discovering Creator’s plan by studying nature;

to classify nature

Linnaeus:

founder of taxonomy; binomial nomenclature

Classification based on anatomy & morphology

-Thought patterns of similarity showed “God plan”

– Domain – Kingdom –Phylum – Class – Order –Family - Genus – Species

– Domains = Eubacteria, Archaea, Eukarya

Carolus Linnaeus1707-1778

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Cuvier:• Paleontologist – studied fossils

• Deeper strata (layers) - very different fossils from current life

• Opposed idea of evolution

• Catastrophism• He used this idea to explain the change in species from deeper strata

• – He said catastrophe destroyed many living species, then repopulated by immigrant species

George Cuvier(1769-1832)

Formation of sedimentary strata with fossils

Hutton / Lyell: (Both used fossil record to show the earth was old)

Gradualism

-geologic change results from slow & gradual, continuous process

Uniformitarianism = -Earth’s processes same rate in past & present � therefore Earth is very old-Slow & subtle changes in organisms � big change

Charles Lyell1797-1875

James Hutton1726-1797

Lamarck:• Published theory of evolution (1809)

» Importance: Recognized that species evolve, although explanation was flawed

» Use and Disuse:

» parts of body used lead to bigger, stronger characteristics

» (eg. giraffe’s neck)

» Inheritance of Acquired Characteristics: modifications can be passed on

Jean-Baptiste Lamarck1744-1829

Malthus:• More babies born than deaths

• Consequences of overproducing within environment = war, famine, disease

• (limits of human pop.)

• Overpopulation leads to a struggle for existence

Thomas Malthus(1766-1834)

Alfred Wallace:• Independently conceived the theroy of evolution and published a paper in 1858

• This prompted Darwin to publish his book on the idea in 1859

• He is really considered a co-founder of evolution

Alfred Wallace(1823-1913)

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II. Charles Darwin (1809-1882)A. English naturalist

B. 1831: joined the HMS Beagle for a 5-year research voyage around the world

C. Collected and studied plant and animal specimens, bones, fossils

D. Notable stop: Galapagos Islands Darwin set sail on the HMS Beagle

around the world & found many new animals

Galapagos Islands

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Galapagos Islands in South AmericaDo not copy

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Some of the organisms that Darwin Studied

Do not copy

Darwin’s Observations

• In the Galapagos Islands Darwin saw giant tortoises, fur-covered seals, lizards that ate cactus plants for food and water, and many birds.

Galapagos

IslndMainland

From his observations, Darwin inferred that a small number of different plant and animal species had come to the Galapagos islands from the mainland.

Darwin’s Observations

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• Darwin reasoned that plants or animals that arrived on one of the Galapagos Islands faced conditions that were different from those on the mainland.

• Perhaps, Darwin thought, the species gradually changed over many generations and became

better adapted to newconditions.

Galapagos Islands

Ecuadorian Jungle

Darwin’s Observations

Similarities &Differences

•Iguanas on the islands had large claws to help them stay on slippery rocks

• Mainland iguanas had small claws for climbing trees.

Mainland

Island

Similarities &Differences

•The cormorants on the mainland were able to fly

• those on the islands were unable to fly.

Mainland

Island

• Once the plants and animals reached the Galapagos Islands they reproduced.

• Eventually, through mutations in their genes, their offspring became different from their relatives on the mainland.

Similarities &Differences

*Remember mutations can be helpful, harmful or neither.

1. Darwin’s Finch Collection from the Islands

a. The birds were all about the same size

b. the shape and size of the beaks of each species were different.

c. This was because each island had different food source

Darwin’s Galapagos Finches

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2. Giant Tortoise

a. On each island the tortoise’s had different shells.

b. Travelers use the shape of the Tortoise shell to determine which island they were on.

III. Darwin’s Conclusion ( Based on his observations)

A. Species were not created in their present form, but evolved from ancestral species. (descent with modification)

B. Organisms with the best traits will survive changes to the environment and pass on their traits

C. Natural selection is the major driving force for evolutionary change of a population

Two-Toed Sloth

IV. Natural Selection is based on 5 facts

A. Variation:Each individual in a species differs from the others.

** Natural selection

requires genetic

variation and

variation must be

inherited genetically

B. Competition: Living things face a constant struggle for existence.

Elk competing for females

**Since food, water,

and living space are

limited, the offspring

must compete with

each other to survive.

C. Overproduction: Too many individuals produced so food/resources are limited

Migrating Wildebeest in Africa

D. Survival of the fittest: Only those individuals that are best suited for their environment survive and reproduce

**Individuals cannot adapt

to their environment; they

are adapted or are not;

adapted individuals will

survive and produce more

offspring

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Helpful variations add up, while unfavorable ones disappear.

Snowshoe Hare in summer and winter

**This hare changes its coat two times a year, exchanging a thin brown summer coat for a heavy, white, fluffy winter coat.

E. The genetic makeup of the population changes. Over time the population has adapted to their environment

**Helpful variations add up, while unfavorable ones disappear.

V. Modes of selectionA. Directional selection favors one of the extremes.

1. Example of Directional selection

2. Pepper Moths -Known as “Industrial Melanism”

a. Dark moths were once rare

b. In the 1850’s, industries created lots of pollution, causing the trees to darken

c. Dark moths were better able to survive. Because they were now camouflaged

d. Lighter moths now stood out & were eaten by the birds

After pollutionBefore pollution

Example of Evolution

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B. Disruptive selection favors both extremes.

C. Stabilizing selection acts against the extremes and favors the middle.

Modes of selection: