Darwin and Evolution
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Outline. History of Evolutionary Thought Darwin’s Theory of Evolution Earth very old Descend with change from a common ancestor Adaptation to a changing environment The Evidence of Evolution Fossil Biogeographical Anatomical Biochemical. Voyage of the HMS Beagle. Charles Darwin at 31.

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  • History of Evolutionary Thought

  • Darwin’s Theory of Evolution

    • Earth very old

    • Descend with change from a common ancestor

    • Adaptation to a changing environment

  • The Evidence of Evolution

    • Fossil

    • Biogeographical

    • Anatomical

    • Biochemical

History of evolutionary thought
History of Evolutionary Thought

  • Prior to Darwin

    • View of nature determined by deep-seated beliefs

    • Held to be intractable truths

    • Biology thought had slowly begun to accept

      • Various ideas of evolution

      • Similarities between living things reflect recent common ancestry

      • Dissimilarities between living things reflect ancient common ancestry

Mid eighteenth century
Mid-Eighteenth Century

  • Taxonomy matured during mid-eighteenth century

    • Linnaeus believed in:

      • The fixity of species

      • That each species had:

        • An ideal structure and function, and

        • A place in the scala naturae (scale of complexity)

    • Count Buffon:

      • Wrote 44-volume catalog of all known plants and animals

      • Suggested descent with modification

Late eighteenth century
Late Eighteenth Century

  • Cuvier:

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

    • Founded Paleontology

    • Proposed Catastrophism

      • Local catastrophes in past had caused later strata to have a new mix of fossils

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

Late eighteenth century1
Late Eighteenth Century

  • Lamarck:

    • First biologist to:

      • Propose evolution

      • Link diversity with environmental adaptation

    • Concluded more complex organisms are descended from less complex organisms

    • Proposed inheritance of acquired characteristics – Lamarckianism

  • Charles Lyell:

    • Earth is subject to slow but continuous cycles of erosion and uplift

    • Proposed uniformitarianism, rates and processes of change are constant

Darwin s theory of evolution
Darwin’s Theory of Evolution

  • Geological observations consistent with those of Hutton & Lyell

  • Biogeographical observations:

    • The study of the geographic distribution of life forms on earth

    • Darwin saw similar species in similar habitats;

    • Reasoned related species could be modified according to the environment

The patagonian hare dolichotis patagonium
The Patagonian Hare,Dolichotis patagonium

Gal pagos islands
Galápagos Islands

  • Tortoises

    • Darwin observed tortoise neck length varied from island to island

    • Proposed that speciation on islands correlated with a difference in vegetation

  • Finches

    • Darwin observed many different species of finches on various islands

    • Speculated they could have descended from a single pair of mainland finch

Natural selection and adaptation
Natural Selection and Adaptation

  • Individuals have heritable variations

  • More individuals produced each generation than environment can support

  • Some individuals have adaptive characteristics

    • Enables increased survival and reproduction

    • Increasing proportion of succeeding generations will have these characteristics

  • Populations become adapted to their local environment through change in individuals

Organisms have variations
Organisms Have Variations

  • Darwin emphasized that individuals from a population vary in their:

    • Functional characteristics

    • Physical characteristics

    • Behavioral characteristics

  • Proposed that these variations:

    • Are essential

    • Allow adaptation to the environment over time

Organisms struggle to exist
Organisms Struggle to Exist

  • Malthus

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

      • Reproductive potential is greater than environment can support

      • Death, disease, and famine were inevitable if population were to have stability

    • Individuals experience a constant struggle for survival

Organisms differ in fitness
Organisms Differ in Fitness

  • Fitness is the relative reproductive success of an individual

    • The most-fit individuals in a population capture a disproportionate share of goodies

    • Interactions with the environment determine which individuals reproduce the most

  • Adaptation

    • Changes that help a species become more suited to its environment

    • Product of natural selection

The evidence of evolution anatomical
The Evidence of Evolution:Anatomical

  • Vertebrate forelimbs:

    • Homologous - All contain the same sets of bones in similar ways

    • Yet they are modified extensively to meet various adaptive needs

    • Darwin interpreted this as support for a hypothesis of common descent

  • Embryological development

    • All vertebrate embryos have:

    • A postanal tail and

    • Paired pharyngeal (gill) pouches

The evidence of evolution anatomical1
The Evidence of Evolution:Anatomical

  • Homologous Structures:

    • Anatomically similar because they are inherited from a common ancestor

    • May be functionally similar or not

  • Analogous Structures:

    • Serve the same function

    • Not constructed similarly

    • Do not share a common ancestor

  • Vestigal Structures:

    • Fully-developed anatomical structures

    • Reduced or obsolete function

The evidence of evolution fossil biogeographical
The Evidence of Evolution:Fossil & Biogeographical

  • Fossil Evidence

    • Fossils record the history of life from the past

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

    • Sometimes the fossil record is complete enough to show descent from an ancestor

  • Biogeographical

    • Distributions of plants and animals across earth

    • Consistent with origin in one locale and then spread to accessible regions

Biochemical evidence
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

  • DNA base-sequence differences:

    • When very similar, suggest recent common descent

    • When more different, suggest more ancient common descent

Significance of biochemical differences
Significance ofBiochemical Differences


  • History of Evolutionary Thought

  • Darwin’s Theory of Evolution

    • Earth very old

    • Descend with change from a common ancestor

    • Adaptation to a changing environment

  • The Evidence of Evolution

    • Fossil

    • Biogeographical

    • Anatomical

    • Biochemical