Darwin's theory of evolution by natural selection

Week 3

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Summary

* Key concepts check

* Explanations of evolutionary change

* Darwin's theory of natural selection

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Discovery of the new world-new observations challenged long-held views-exposure to new plants and animals increased awareness of biodiversity

Disconfirmed: fixity of species and a young Earth

*Scientists sought better explanations to:-replace the disconfirmed ones-explain why biological organisms evolve

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Historical context

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John Ray (1627-1705)Species: reproductively isolated populations able to produce infertile offspring

Carolus Linnaeus (1707-1778)Binomial Nomenclature: using Genus species as scientific names to organize biodiversity

Georges Cuvier (1769-1832)Catastrophism: today's geologic features resulted from catastrophic events-first to coin the term extinct

Charles Lyell (1797-1875)Uniformitarianism: processes happening today were the same in the past

RECAP SLIDE

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Comte de Buffon (1707-1788)Changes in the environment correlated with changes in plants and animals

Jean-Baptiste Lamarck (1744-1829) - Inheritance of acquired characteristicsSpecies change influenced by environmental changeFirst to really attempt and explain evolutionary process

Species aren't fixed, they change, they evolve

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-Grew up in well-educated family-1830s: served as naturalist on the HMS Beagle

Observations:

-sexual reproduction increases variation in species

-the importance of biological variation within a species

Charles Darwin (1809-1882)

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Thomas Malthus (1766-1834)Populations: grow exponentially Available resources: 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

Importance of environmental pressures

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-Every new generation has more offspring born than can survive (1)-There's constant competition for resources (2)-There's biodiversity among individuals in a generation (3)

If all three of these circumstances are evident, then "favorable variations would tend to be preserved, and unfavorable ones to be destroyed. The result would be the formation of a new species" (Origin of Species)

Key observations influencing Darwin

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Artificial selection-All domestic dogs share a common ancestry-There's extreme variation exhibited by dog breeds due to artificial selection

Natural selection in detail - analog with artificial selection

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Artificial selectionWild ancestor to bananas - solid seeds!

Natural selection in detail - analog with artificial selection

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1. All species are capable of producing offspring at a rate faster than the production of resources (like food)Influenced by Malthus

2. There's biological variation within all speciesInfluenced by Buffon, Lamarck, etc

3. In each generation, more individuals are produced then can survive, because limited resources create competitionInfluenced by Malthus

Natural selection in detail - Eight processes

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4. Individuals with favorable variations or traits have an advantage over those lacking said traits.I.e., Individuals have a greater fitness because of favorable traits increasing the likelihood of survival and reproductionMinor influences from Lamarck

Natural selection in detail - Eight processes

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5. Environmental context determines whether a trait is favoredImportance of environment influenced by Buffon and Lamarck

6. Traits are inherited and passed on to the next generation-because individuals with favorable traits contribute more offspring to the next generation, they have greater reproductive success i.e., fitnessDarwin's addition, independently conceived by Wallace too

Natural selection in detail - Eight processes

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7. Successful variations accumulate over long periods of time, so later generations may be distinct from ancestral ones.I.e., a new species may appearLyell's uniformitarianism allowed for the plausibility of a slow evolutionary process

8. Geographical isolation contributes to formation of new species as individuals adapt to different environments and respond to different selective pressuresInfluenced by observations and Wallace's biogeography

Natural selection in detail - Eight processes

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8. Geographical isolation contributes to formation of new species as individuals adapt to different environments and respond to different selective pressuresInfluenced by observations and Wallace's biogeography

Natural selection in detail - Eight processes

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Fitness: a measure of relative reproductive success of individuals-measured by an individual's genetic contribution to the next generation compared to other individuals

Reproductive success: number of offspring an individual produces and rears to reproductive age

Selective pressure: forces in the environment that influence reproductive success in individuals-what causes distinct species to develop

Important terms for evolution by natural selection