Chapter 2: Origins of modern biology and Darwin's Theory of Natural - - PowerPoint PPT Presentation

Chapter 2: Origins of modern biology and Darwin's Theory of Natural Selection

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Summary of this week (and next Tuesday)

• 1. Update on the class
• 2. Very brief description of evolution
• 3. Pre-scientific thought
• 4. Recall the idea of scientific explanation
• 5. Evaluate Pre-scientific explanations
• 6. Survey Scientific Revolution's key figures influencing Darwin's theory of

natural selection

• 7. Natural selection

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• 2. Very brief description of evolution

Evolution: change in the genetic composition of a population

• ver time
• framework we use to understand biology

Misconceptions: evolution is uncontroversial in science but controversial outside of science

• most controversy involves the theories that attempt to explain

evolutionary change Darwin's theory of evolution by natural selection is controversial outside of science but not controversial within science.

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• 3. Pre-scientific thought

Primary explanations of nature before the late 17th century *Fixity of species: all biological organisms were created at the same time with the came features we see today *Young Age of the Earth: Earth was created 6,000 years ago (6 kya)

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• 3. Pre-scientific thought

Primary explanations of nature before the late 17th century *Fixity of species: all biological organisms were created at the same time with the came features we see today *Young Age of the Earth: Earth was created 6,000 years ago (6 kya) At the start of the 18th century

• observations of biological diversity from the New World

could not be explained by these accounts

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Recall from chapter 1

Hypotheses: tentative explanations of facts/observations Scientific method: Observation -> Hypothesize -> Test x a billion -> Theory Theories: tested and confirmed explanations of facts/observations Hallmarks of good hypotheses Disconfirmable Make testable predictions

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• 4. Recall the idea of scientific explanation

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Abductive reasoning: Inferring the best explanation for specific facts. All mammals have hair. Whales have hair. If whales are mammals, then it makes sense that they have hair. Therefore, whales are probably mammals. Another example https://www.youtube.com/watch?v=ycH9dGXq13w What are the facts? Beavis' hypothesis: this sucks. How can we say this is the best explanation of the facts?

Hallmarks of good hypotheses

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Ask: Does the hypothesis make testable predictions? Ask: Is the hypothesis disconfirmable? The best theories in science are disconfirmable. The best theories in science make predictions. EVERY explanation (hypotheses, theories, postulates, whatever) should have these hallmarks ALL of the topics in this course should rely on explanations with these hallmarks

Disconfirmation

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Disconfirmable: identifying evidence against our hypothesis E.g., Hypothesis: All wood burns If I find wood that doesn't burn then that's evidence against the hypothesis, i.e., it would disconfirm the hypothesis Disconfirmed hypotheses are either modified or rejected New fact: Someone delivers wood to my door which won't catch on fire. Ad hoc modification: all wood burns except if it's been delivered to my doorstep except if it's delivered on Mondays except if it's log-shaped, too Ad hoc modifications only attempt to amend problems undermining the original hypothesis Hypothesis eventually becomes messy or useless Can no longer disconfirm the hypothesis

Non-ad hoc modifications make testable predictions

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Testable predictions: if the hypotheses is correct, then it should be able to predict what observations we could make if

• 5. Evaluate Pre-scientific explanations

Set of facts by the end of the 1600s The same animals found in europe are found around the world These animals vary in size These animals vary in color Size and color both tend to match the environment Hypothesis: All living things were created as is and haven't changed

• Set of facts by the end of the 1600s

Some trees grow one ring every year Some trees have 9,000 rings Hypothesis: Everything including the Earth was created 6,000 years ago.

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Classification - the language

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John Ray (1627-1705)

• Grouped organisms

by reproductive viability

• First to use "species"

and "Genus" Carolus Linnaeus (1707-1778)

• Binomial Nomenclature

E.g., Homo sapiens, Tyrannosaurus rex, etc.

• Taxonomic classification of

biological organisms

Change - the relationship between environment and organism

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Comte de Buffon (1707-1788)

• Plants and animals interacted with the environment
• Environmental changes correlated with changes in

plants and animals

Precursors - Dynamic Biology

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Jean-Baptiste Lamarck (1744-1829)

• Species alter their characteristics to

meet their environment.

• First to really attempt and explain

evolutionary process

Precursors - Ancient age of the Earth

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Charles Lyell (1797-1875)

• Father of modern geology

Uniformitarianism: The gradual processes happening today were the same in the past. Georges Cuvier (1769-1832)

• Extinction
• Catastrophism

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Thomas Malthus (1766-1834)

• populations grow exponentially
• food supplies/production grow

arithmetically

• populations outgrow food

supply - survival of individuals dependent on access to food supply or resources Alfred Wallace (1823-1913)

• Independently generated the

concept of Natural Selection

• Father of Biogeography

Precursors - Environment influences organisms

• heavily influenced by these thinkers

*5 year voyage on the HMS Beagle

• What he observed informed his theory explaining why things change.

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• 7. Darwin and natural selection

How Darwin changed the natural sciences

Darwin's theory of natural selection explains what guides evolutionary change

Took all the best parts of theories posited by the thinkers we just surveyed and made one that we still use today.

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Natural Selection - Initial requirements

Individuals with favorable variations --> survive and reproduce at higher rates

• 1. Populations grow faster than the growth of available resources.
• 2. Populations have differential variation among members
• 3. More offspring are produced than survive due to competition for resources.
• 4. Individuals with favorable traits (speed, disease resistance, size) are more likely to survive* than

individuals without those traits.

Fitness - A relative measure of reproductive success. *Not who can live the longest but who can survive long enough to reproduce.

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Natural Selection

• 5. Favorable traits determined by environmental context
• 6. Offspring resemble their parents - favorable traits are inherited

Reproductive success - favorable traits are inherited and become more common.

• 7. This favorable variations accumulates in a population over many generations so newer generations are

distinct from ancestral generations. New species emerge

• 8. Geographical isolation - populations become geographically isolated and over time they respond to

selective pressures - different ecological contexts - to become distinct species.

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Natural Selection in Action

Reproductive success - favorable traits are passed on with a higher frequency compared to less advantageous traits which decrease in frequency over time. Selective pressures - Environmental forces influencing the reproductive success. Fitness - A relative measure of reproductive success. Adaptations - The evolutionary shifts in the variation of traits in a population in response to environmental changes.

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Natural Selection in Action

Peppered Moths Industrial melanism in populations of peppered moths documented. Shifts of pigment pattern frequencies in response to the change in the environment.

Such responses are called adaptations.

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Natural Selection in Action - Finches

WHAT: Galapagos island finch population

• Beak thickness changed over time
• a favorable trait (thicker beaks) confers a

selective advantage in a population over time.

• thick beaks had greater reproductive success

during droughts.

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Natural Selection in Action - Finches

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Finches competed for limited resources Members of finch population varied in beak size

E.g., 13 species among the Galapagos Islands

Natural Selection - Insights Gained from examples

• 1. Traits are inherited - otherwise natural selection cannot act
• 2. Populations of individuals exhibit biological variation of characteristics
• Selection also only works on pre-existing variation!
• 3. Fitness is relative - it changes relative to environmental change
• Finch beak size correlated with extended periods of drought on the islands
• 4. Natural selection only acts on traits that affect reproduction
• Traits expressed after an organism reproduces are not influenced by natural selection

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Natural Selection - Main Points

*Darwin was able to recognize that it was variation among the individuals of a population that contributed to the change in a species over time. Think about clones. Natural selection operates on individuals but it is the population that evolves

Unit of Natural Selection - Individual Unit of Evolution - Population Individuals don't change genetically but overtime populations do.

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Common Ancestry - Finches

Evolution demonstrated in the finch populations found on the Galapagos islands

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John Ray (1627-1705)

• Identified reproductive isolation of species
• First to use "species" and "Genus"

Carolus Linnaeus (1707-1778)

• Binomial Nomenclature
• Taxonomic classification of biological
• rganisms

Comte de Buffon (1707-1788)

• Plants and animals interacted with the

environment

• Changes in the environment correlated with

changes in plants and animals Jean-Baptiste Lamarck (1744-1829)

• Species change influenced by environmental

change

• First to really attempt and explain evolutionary

process James Hutton (1726-1797)

• First to use Uniformitarianism
• the processes we see today to explain the geological history
• f our planet

Georges Cuvier (1769-1832)

• Extinction
• Catastrophism

Charles Lyell (1797-1875)

• Father of modern geology
• The processes happening today were the same in the past:

Uniformitarianism Alfred Wallace (1823-1913)

• Independently generated the concept of Natural Selection
• Father of Biogeography

Thomas Malthus (1766-1834)

• Populations grow exponentially while food

supplies/production grow arithmetically

• Populations outgrow food supply - survival of individuals

dependent on access to food supply or resources

Precursors Recap

Study Guide

• Know what the subfields of anthropology are. Know the subfields of physical anthropology, too.
• Know the different parts and order of the scientific method
• Be prepared to identify the famous thinkers of the scientific revolution and connect them with their

contributions

• Be prepared to discuss uniformitarianism, natural selection, fitness, selective pressure, etc. and other

concepts. Key Terms Culture Natural selection Disconfirmation Reproductive success Hypothesis Theory Fixity of species Catastrophism

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