PRINCIPLES OF EVOLUTION

Sections 16.1-16.3

In science, the term "Theory" does not express doubt.

• In science, the term theory is used to represent ideas and explanations that have been confirmed through tests and observations

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• The theory of evolution remains one of the most useful theories in biology because it explains many questions and observations.

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Darwin’s Voyage of Discovery�Born: February 12, 1809

• KEY CONCEPT �Darwin’s voyage provided insight on evolution.
• Wanted to explain biological diversity he observed scientifically
• He did this in 3 ways.
• Species vary globally.
• Species vary locally.
• Species vary over time.

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The Journey of the H.M.S. Beagle

• 5 year voyage mapping coastline of South America
• One of the most important scientific voyages in history

Darwin’s Voyage of Discovery

• Species vary globally.
• He noticed that different, yet ecologically similar, animal species inhabited separated, yet ecologically similar, habitats around the globe.
• Example: Flightless bird
• Grasslands in South America: rhea
• Africa: ostrich
• Australia: emu

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Rhea

Ostrich

Emu

Darwin’s Voyage of Discovery

• Species vary locally.
• He noticed that different, yet related animal species occupied different habitats locally.
• Example: 2 species of rheas living in South America
• One in Argentina’s grassland
• Other in the colder, harsher grass and scrubland to the south.

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Darwin’s Voyage of Discovery

• Species vary locally.
• Example: Galapagos Islands (Off Pacific coast of South America)
• Islands are close to one another
• Saw differences among giant land tortoise

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Galapagos Island Tortoises

• Isabela Island: high peaks, rainy, vegetation close to ground…dome shaped shell and short neck
• Hood Island: flat, dry, and sparse vegetation…curved and open around neck and long neck

Darwin’s Voyage of Discovery

• Species vary locally.
• Example: Species of mockingbirds vary as well from island to island.

Darwin’s Voyage of Discovery

• Species vary over time.
• While unearthing fossils on his voyage, he discovered the long-extinct Glyptodont, a giant armored animal similar to an armadillo.

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Why had glyptodonts disappeared? And why did they resemble armadillos?

Armadillo

Putting the Pieces Together…

• On his way home, he thought of patterns he had seen.

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• The evidence suggested that species are not fixed and that they could change by some natural process.

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Section 16.2-Ideas That Shaped Darwin’s Thinking�

• An Ancient, Changing Earth
• By Darwin’s time, new science of geology was providing new and different ideas.
• Important scientists:
• James Hutton:
• Originated theory of uniformitarianism, which says that Earth’s crust formed naturally through geologic means
• “Father of Geology”

Ideas That Shaped Darwin’s Thinking

• An Ancient, Changing Earth
• Charles Lyell:
• Popularized uniformitarianism.
• Agreed that Earth was very old
• Wrote a book called “Principles of Geology”

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Ideas That Shaped Darwin’s Thinking

• Lyell impacted Darwin much!

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• Earthquake, repeated many times over many years, could build South America’s Andes Mountains—a few feet at a time.

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• Rocks that had once been beneath the sea could be pushed up into mountains.

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• Darwin asked himself, if Earth can change over time, could life change too?

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Andes Mtns. on west coast of South America

Ideas That Shaped Darwin’s Thinking

• Jean-Baptiste Lamarck (1809)
• All organisms have an inborn urge to become more complex and perfect

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• Organisms could change the size or shape of their organs by using their bodies in new ways.
• Example: Black-necked stilt grow longer legs to wade in deeper water and would pass to offspring

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Principle: Inheritance of Acquired Traits

Ideas That Shaped Darwin’s Thinking

• Why are Lamarck disproven?
• Organisms don’t have an inborn drive to become more perfect.

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• Traits acquired by individuals during their lifetime cannot be passed on to offspring.

Why? Logically it doesn't work. Imagine if you were in a car accident and had a leg amputed. This does not mean that your children will only have one leg. Features gained during life are not passed on to children.

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Ideas That Shaped Darwin’s Thinking

• Thomas Malthus (1798)

Scientist who said that if the population of human grew too large, they would be reduced by famine, disease, and war.

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1. Proven to be inaccurate

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2. Failed to foresee impact of science & technology on food supply

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Artificial Selection

• Process in which nature provides the variations, but humans select those they find useful.
• See fancy pigeon varieties below…

Ideas That Shaped Darwin’s Thinking

• CONCLUSION:
• Darwin saw variation in wild and domesticated species.
• Recognized natural variation as important because it provided the raw material for evolution.

Section 16.3: Darwin Presents His Case

• Natural selection is a mechanism by which organisms with variations most suited to their local environment survive and leave more offspring.

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

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• In natural selection, the environment-not farmer or animal breeder-influences the fitness.

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• Darwin proposed that adaptations arose over many generations.

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Examples of Adaptations:

Leaf Bug

Scorpionfish

Cactus spines

Coral snake

Scarlett King Snake

Darwin Presents His Case

• Many adaptations involve behaviors.
• Example: Crane scaring off an approaching fox, birds building a nest, kangaroo boxing, correct blinking rate in firefly

Darwin Presents His Case

• Natural selection explains how evolution can occur.
• Natural selections occurs in these 4 ways.
• The Struggle for Existence
• Variation
• Survival of the Fittest
• Descent with Modification

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Darwin Presents His Case

1. The Struggle for Existence

• Organisms often produce more offspring than will survive.

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Darwin Presents His Case

• Variation
• Increases chances of survival and reproduction
• Green color is an adaptation and blends better…THEY ARE NOT EATEN BY PREDATORS!

Darwin Presents His Case

3. Survival of the Fittest

The environment “favors” certain variations

i. Better competitors

• For food (Darwin’s finches)
• For mate (peacock, iguanas)

ii. Avoid predators (peppered moth)

iii. Antibiotic resistance (bacteria)

b. Organisms with favorable traits are more likely to survive and reproduce

• These organisms have a high “fitness”
• Fitness is the measure of survival ability and ability to produce more offspring.
• “Good” genes become more frequent

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Darwin Presents His Case

4. Descent with Modification

• Over time, natural selection will result in species with adaptations that are well suited for survival and reproduction in an environment.

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Darwin Presents His Case

• Natural selection acts on existing variation.
• Natural selection can act only on traits that already exist.
• Structures take on new functions in addition to their original function.

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Darwin Presents His Case

• Populations Do Change Over Time

1. Macroevolution: Gradual change from one species to another

• Unobservable and unrepeatable

2. Microevolution: Change within a species

• Can be observed
• It is a Fact that organisms evolve → change over time

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Can see

Can’t see

Can’t see

Can see

Section 16.3- Theory of Natural Selection

• Journaling
• Suppose that sea lions living in the Galapagos suddenly lose their main food source when changes in currents and sea temperature keep anchovy away from the islands. The only other food available is a small species of crab that lives on the sea floor 100 feet below the surface. Discuss the traits in the sea lion population that might be adaptive and how the population could change. Write a description of two possible outcomes.