Evolution and Natural Selection

Intellectuals / Ideas in Darwin’s Era

American Revolution French Revolution U.S. Civil War1900185018001750

1795

1809

1798

18301831–1836

1837

1859

18371844

1858The Origin of Species is published.Wallace sends his hypothesis to Darwin.

Darwin begins his notebooks.Darwin writes essay on descent with modification.

Darwin travels around the world on HMS Beagle.

Malthus publishes “Essay on the Principle of Population.”

Lyell publishes Principles of Geology.

Lamarck publishes his hypothesis of evolution.

Hutton proposes his theory of gradualism.

Linnaeus (classification)

Cuvier (fossils, extinction)Malthus (population limits)

Lamarck (species can change)Hutton (gradual geologic change)

Lyell (modern geology)Darwin (evolution, natural selection)

Wallace (evolution, natural selection)

The French ConnectionCuvier – 1700’s – 1800’s French naturalist,

examined fossils he believed to be more than a few thousand years old. Noted similarities between fossils and living creatures.

Lamarck – 1800’s French naturalist, tried to explain Buffon’s observations.

• Species are not permanent, life changes or evolves. Evolution explained as a process of adaptation.

“Inheritance of acquired characteristics”

Great Scots!

Hutton – late 1700’s Scottish geologist, proposed Earth was formed the same way we see changes occurring today. Gradual change that can be immense over time.

Lyell –early 1800’s Scottish geologist, furthered Hutton’s ideas. • Erosion and earthquakes are

geologic processes that can account for the changes in Earth’s physical features.

Can’t stop the pop...ulation growth

Malthus – early 1800’s British demographer, observed that populations grow exponentially while resources do not, led to the explanation of disease and competition as components of man’s “struggle for existence”.

Q: Population curves upward, resources go down as they are used up. Then what happens?

Clearly there were many contributors to the theory of

evolution…Charles Darwin: name

most associated with evolution• did not publish his views on

the subject until 1859• Why were his ideas radical?

Look at what people thought at the time:

Earth was less than 10,000 years oldFixed species – species do not change

The Beagle sets sail

1831: HMS Beagle embarks on a ‘round-the-world voyage. • Mission? Chart South American coastline for the

British Navy. • 22 year old biologist, Charles Darwin, was aboard.

• Through specimens he collected, pictures he

sketched, and journals he kept, Darwin’s ideas began to change. He left with many of the beliefs common in his time. By the time he returned to England, he had seen things that began to make him question…

What did he observe?• Many species of South America:

• Similar to European species, but quite distinct at the same time.

• Marine fossils high in the mountainous regions.• Experienced an earthquake where an underwater

landmass was heaved up above the water level • Exposed it to environment for the first time. • Concluded that this could be along the lines

of what Hutton and Lyell had explained in their theories.

• Galapagos Islands: Young volcanic islands that had many similar species to the mainland, but were different, even from island to island. • Darwin’s idea was similar to that of

Lamarck’s … that the species must have adapted to the new environment.

5 years later…Putting it all together

• Darwin had a large collection of fossils, volumes of journals, and had seen organisms that varied greatly from place to place.

• After his return, he had developed 2 new ideas based on his experience:

• The Earth was old.• Species change.

• If species change, it must be for a reason. What is the reason?

• Selective breeding of livestock and animals leads to a change (artificial selection), but that is not what happens in nature.

• Malthus’ ideas of competition struck a chord, Darwin proposes that this must be what drives the changes.

Darwin’s Ideas• He writes his ideas in 1844, about the origin of species

and natural selection, only tells a few colleagues of his ideas

• Does not complete his writings until 1858, when he received a manuscript from Alfred Wallace, who had developed a similar theory of natural selection.

• 1859: Darwin publishes his ideas a year later in On the Origin of Species. He outlines two main points:

Descent with modification – based on evidenceNatural Selection – the mechanism for evolution

When the Industrial Revolution began, it was coal powered. What does coal produce when burned? What do you think happened to the forests around newly industrialized towns?

In those forests lived the peppered moth. It came in two colors, but it was mostly light gray. What happened after the revolution?

Click here to see a simulation!

What is evolution by natural selection?

Evolution: Cumulative change in the

heritable characteristics of a

population.

1) Populations tend to produce more offspring than the environment can support. “Hey! There aren’t enough

resources to go around!”

This causes a struggle for existence.

How does evolution happen?

2) Individuals within a population are varied.

How do we explain this natural variation?This means that some individuals are going to be more successful in that struggle for existence than others!

They will survive longer and reproduce more.

3) Characteristics are heritable!

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Those individuals who survive and reproduce will have offspring with similar traits. Over time, these favorable traits will become more and more abundant in the population.

How do we represent evolution?

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Cladogram Represents the

evolutionary relationship between species

Based on the similarities /differences in their physical or genetic characteristics

Nodes (where branches meet) represent the common ancestors of those species

Which are more closely related? A, B, or C?

Cladograms

Evidence: Fossil Record Most fossils found in

sedimentary rock Fossil record is

formed due to layering Older rock is

“lower” than younger rocks

Can also date using radiometric dating- calculate the age from the amount of radioactive isotopes present in the rock.

Evidence: Structural SimilaritiesSkeletal structures are very similar in

parts of different animals.

Human, feline, whale, and bat limbs are similar

Homologous structuresstructures that indicate common ancestry

Vestigial structuresstructures that have a major function in one organism, but have lost it in another

whale femur bones, wisdom teeth, tailbone

http://www.youtube.com/watch?v=OAfw3akpRe8&feature=BFa&list=UUZYTClx2T1of7BRZ86-8fow

Evidence: Developmental Similarities Developing embryos of different organisms

appear similar during maturation, and distinctive differences develop later in the process

Evidence: Molecular Biology In the era of DNA, we can use the ultimate similarity of

life and compare DNA sequences to see how closely organisms resemble one another.

The closer the DNA sequences, the closer related

The less the sequencesmatch, the further the

relationship