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Darwin and Evolution Chapter 17 History of Evolutionary Thought Prior to Darwin, most people had a mindset determined by deep-seated beliefs held to be intractable truths Biology during preceding century had slowly begun to accept the idea of evolution

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History of Evolutionary Thought

  • Prior to Darwin, most people had a mindset determined by deep-seated beliefs held to be intractable truths

    • Biology during preceding century had slowly begun to accept the idea of evolution

    • Living things share common characteristics due to common ancestry

Mader: Biology, 9th Ed.


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Mid-Eighteenth Century

Taxonomy was an important endeavor during mid-eighteenth century

  • Carolus Linnaeus

    • Special creation – each species has an ideal structure and function

    • Fixity of species – each species had a place in the scala naturae(sequential ladder of life)

Mader: Biology, 9th Ed.


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Mid-Eighteenth Century

Count Buffon wrote 44-volume natural history describing all known plants and animals

  • Provided evidence of descent with modification

  • Influences of the environment, migration, geographical isolation, and the struggle for existence

Mader: Biology, 9th Ed.


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Mid-Eighteenth Century

Erasmus Darwin

  • Suggested common descent based on:

    • Changes undergone by animals during development

    • Artificial selection by humans

    • The presence of vestigial organs

Mader: Biology, 9th Ed.


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Late Eighteenth Century

George Cuvier

  • First to use comparative anatomy to develop a system of classification

  • Founded Paleontology

  • Proposed Catastrophism

    • Hypothesized local catastrophes had occurred whenever a new strata showed a new mix of fossils

    • After each catastrophe, a region was repopulated by species from surrounding areas.

Mader: Biology, 9th Ed.


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Late Eighteenth Century

Lamarck

  • First biologist to believe evolution occurs

  • First to link diversity with environmental adaptation

  • Concluded more complex organisms are descended from less complex organisms

  • Inheritance of acquired characteristics (Lamarckianism)

    • Giraffes stretch necks and then pass on long necks to offspring

Mader: Biology, 9th Ed.


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Late Eighteenth Century

Charles Lyell

  • Supported a theory that the earth was subject to slow but continuous cycles of erosion and uplift

  • Uniformitarianism rates and processes of change are constant

Mader: Biology, 9th Ed.


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Darwin’s Theory of Evolution

Mader: Biology, 9th Ed.


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Darwin’s Theory of Evolution

  • Occurrence of Descent

    • Darwin was not convinced of uniformitarianism, but did believe the earth was very old

    • Enough time for descent with modification

Mader: Biology, 9th Ed.


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Biogeography

  • Biogeography is the study of the geographic distribution of lifeforms on earth

    • Darwin saw how similar species in similar habitats

    • Reasoned related species could be modified according to the environment

Mader: Biology, 9th Ed.


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Galápagos Islands

  • Tortoises

    • Darwin noticed tortoise neck length varied from one island to next

    • Proposed that tortoise speciation on islands could be correlated with a difference in vegetation among the islands

Mader: Biology, 9th Ed.


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Galápagos Islands

  • Finches

    • Darwin observed different species of finches on various islands

    • Speculated that all the different types of finches could have descended from a single type of mainland finch

Mader: Biology, 9th Ed.


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Natural Selection and Adaptation

  • Natural selection proposed as a driving mechanism of evolution caused by environmental selection of organisms most fit to reproduce, resulting in adaptation

Mader: Biology, 9th Ed.


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Three Preconditions for Natural Selection

  • Individuals have heritable variations

  • Many more individuals are produced each generation than the environment can support

  • Some individuals have adaptive characteristics enabling increased survival and reproduction

Mader: Biology, 9th Ed.


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Two Consequences of Natural Selection

  • Increasing proportion of succeeding generations have these characteristics

  • Populations become adapted to their local environment

Mader: Biology, 9th Ed.


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Organisms Have Variations

  • Darwin emphasized members of a population vary in their functional, physical, and behavioral characteristics

    • Believed variations were essential

    • New variations as likely to be helpful as harmful

    • Heritable variations allow adaptation to the environment

Mader: Biology, 9th Ed.


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Variation in a Population

Mader: Biology, 9th Ed.


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Organisms Struggle to Exist

  • Malthus stressed the reproductive potential of human beings

    • Proposed death and famine were inevitable due to rapid population growth

    • Each generation has the same reproductive potential as the previous generation

    • Constant struggle for existence

Mader: Biology, 9th Ed.


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Organisms Differ in Fitness

  • Fitness is the relative reproductive success of an individual

    • Most-fit individuals capture a disproportionate amount of resources

    • In nature, interactions with the environment determine which members of a population reproduce to a greater degree

      • Artificial Selection

Mader: Biology, 9th Ed.


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Artificial Selection

Mader: Biology, 9th Ed.


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Artificial Selection in Plants

Mader: Biology, 9th Ed.


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Organisms Become Adapted

  • An adaptation is a trait that helps an organism become more suited to its environment

    • Product of natural selection

Mader: Biology, 9th Ed.


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The Evidence of Evolution

  • Fossil Evidence

    • Fossil record is the history of life recorded by remains from the past

    • Documents a succession of life forms from the simple to the more complex

    • Sometimes the fossil record is complete enough to allow a trace of the evolutionary history of an organism

Mader: Biology, 9th Ed.


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Transitional Fossils

Mader: Biology, 9th Ed.



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Biogeographical Evidence

  • Distributions of many plants and animals across earth consistent with hypothesis that when forms are related, they evolved in one locale and then spread to accessible regions

    • Marsupials

Mader: Biology, 9th Ed.


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Biogeography

Mader: Biology, 9th Ed.


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Anatomical Evidence

  • Darwin was able to show a common descent hypothesis offers a plausible explanation for anatomical similarities among organisms

    • Despite dissimilar functions, all vertebrate forelimbs contain the same sets of bones in similar ways

Mader: Biology, 9th Ed.


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Anatomical Evidence

  • Homologous Structures are anatomically similar because they are inherited from a common ancestor

  • Analogous Structures serve the same function, but are not constructed similarly, and do not share a common ancestor

  • Vestigal Structures are fully-developed anatomical structures developed in one group of organisms, but reduced, and may have no function, in similar groups

Mader: Biology, 9th Ed.


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Significance of Homologous Structures

Mader: Biology, 9th Ed.



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Biochemical Evidence

  • Almost all living organisms

    • Use the same basic biochemical molecules

    • Utilize same DNA triplet code

    • Utilize same 20 amino acids in their proteins

  • When the degree of similarity in DNA base sequences are compared, the data suggest common descent

    • When very similar, suggest recent common descent

    • When more different, suggest more ancient common descent

Mader: Biology, 9th Ed.


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Biochemical Differences

Mader: Biology, 9th Ed.


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Mader: Biology, 9th Ed.

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