Ch. 2 Scientific thought and Darwin's theory of natural selection · 2019. 4. 7. · -a 5-year...

Ch. 2 Scientific thought and Darwin's theory of natural selection

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The anthropological perspective

Holistic approach to science

Ethnocentrism: viewing other cultures from the inherently biased perspective of one's own culture

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Pre-scientific thinking

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Common views before the 18th century

Fixity of species

Young Earth

Pre-scientific thinkingChanges before the 18th century

-discovery of the New World

-new tools (e.g., telescope)

-heliocentrism

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Precursors to evolutionary theoryJohn Ray:

species: a group of organisms that are reproductively isolated

Carolus Linnaeus: binomial nomenclatureE.g., Homo sapiens = Genus species

Precursors to evolutionary theoryGeorges-Louis Buffon: posited a correlation between changes in the environment and changes in an organism

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Precursors to evolutionary theoryJean-Baptiste Lamarck: emphasized organism-environment interaction

First to try and explain evolution...Inheritance of acquired characteristics

-traits altered through use or disuse-altered traits are inherited

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Precursors to evolutionary theoryJean-Baptiste Lamarck: emphasized organism-environment interaction

First to try and explain evolution with:Inheritance of acquired characteristics

-traits altered through use or disuse-altered traits are inherited

Problem: says traits are altered during the lifetime of an individual

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Georges Cuvier: tried to explain geology with catastrophism-first to say species go extinct

Charles Lyell: Uniformitarianism explains geology points to an old Earth

https://youtu.be/o_wmulBtWlk

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Thomas Malthus: populations grow exponentially but resources grow linearly

-leads to competition for resources

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-learned about Lamarck, Buffon, etc.-BFFs with Lyell-a 5-year voyage around the world inspired his theory of natural selection

Charles Darwin (1809-1882)

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Artificial selection-All dogs share a common ancestor-Explains the extreme variation between breeds

Natural selection: artificial selection analogy

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Individuals with favorable traits have higher reproductive success compared to individuals with less favorable traits.

(1) all species produce offspring faster than the food supply

(2) there's biological variation in all species

(3) each generation more offspring are born than survive

Natural selection in detail - Eight processes

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(4) more favorable traits lead to more fit individuals

(5) environment determines which traits are favorable

(6) traits are inherited and passed on to yield greater reproductive success

Natural selection in detail - Eight processes

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(7) over time, changes accumulate leading to new species

(8) geographical isolation leads to new species through selective pressure

Natural selection in detail - Eight processes

Reproductive success: # of reproductively viable offspring produced

Fitness: relative measure of reproductive success

Selective pressures: environmental factors determining reproductive success.

https://youtu.be/Uf-mOCN7rUUhttp://peppermoths.weebly.com/

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Important terms for evolution by natural selection

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Natural selection

Examples of natural selection: Galapagos finches-Local environmental conditions varied from island to island

SO: NS led to different populations to diverge from each other

*beak size and structure differ between species

Heavy beaks = exploit seeds and leaves

Long stout beaks = exploit insects in trees (like a woodpecker)

Long thin beaks = exploit flying insects

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NS ex: Antibiotic resistance in bacteria

Environmental pressure: use of antibioticsSelection for: higher resistance to antibiotics-Over many generations, a new resistant bacteria emerges.

https://youtu.be/CUslKICi5mc(antibiotics as evidence)

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Examples highlight important conditions needed for natural selection

i. Only acts on heritable traits

ii. Only acts on already existing variation

iii. Fitness is relative to environmental changes

iv. Only acts on traits that affect reproduction

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Recap of Darwin's theory of natural selection

-mechanism explains evolutionary change-influenced by previous scientists and Darwin's observations.

-all species have variation of heritable traits among individuals

-traits are advantageous (increase reproductive success) relative to environmental context

-gradual accumulation of advantageous traits lead to new species.

-new species can also arise due to geographic isolation.

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Sexual selection

Selection for traits increasing male success in mating-selection mostly for traits expressed in males-traits seem useless/harmfulBUT harm outweighed by male success in mating

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Question: What environmental pressures would make a wolf population gradually evolve into a chihuahua population?

Brainstorm: What are traits wolves have?What are traits chihuahuas have?

Exercise: Dog breeding

Keep in mindNatural selection operates on individuals but its populations that evolve

Individuals = unit of NS

Populations = unit of evolution

Populations, species, genera, families, orders,... evolve

Favorable traits same as saying advantageous traits same as saying adaptive traits

-text uses these phrases interchangeably to refer to the same thing

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ID is unfalsifiable-can't differentiate between designed and natural-saying the designer is intelligent doesn't help

ID is unfalsifiable: no observations disconfirm it

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What's a good design hypothesis?

We use design to explain things all the time

Good design hypotheses-based on background knowledge of intentions

Intentions: reasons/goals a designer has to make something

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Intentions: reasons/goals a designer has to make something

Chicken and pug designed by artificial selectionIntentions: wanted an animal to make eggs; wanted pet that looks cute (apparently)

When archaeologists find arrowheads they infer designed based on background knowledge that humans design tools for hunting

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What's a good design hypothesis?

Intelligent design is a terrible explanationScience shouldn't exclude hypotheses if they're good explanations

Intelligent design (ID): everything in biology was designed by an intelligent being.

-No background knowledge of the intelligent designer's intentions-Don't know the reasons why a designer would make humans

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Intelligent design is a terrible explanationScience shouldn't exclude hypotheses if they're good explanations

Intelligent design pales in comparison to competing explanations

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Intelligent design is a terrible explanation

Three best criticisms of ID

1. ID is unfalsifiable2. Lack background knowledge of the designer's intentions3. ID can't compete with rival explanations like evolutionary theory

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Constraints on Darwin's theory of natural selectionConstraint: Didn't know why biological variation occurs

Constraint: Didn't know how traits were inherited traits

Overcame constraints due to:-advancements in technology, cell biology, and genetics-the rediscovery of Mendel's principles of inheritance

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