Charles Darwin & the Origins of Natural Selection
    Who is Darwin & what did he do?
    What is Natural Selection & how does it work?
    How does Natural Selection explain Evolution?
As of early 1800s:

Fact: current life forms differ from those of previous times,
            as shown be successive geological strata
    Organic change has occurred

 Fact: current life forms extremely variable,
          both within & among species.
                  Variation occurs in time & space

Why question transmutes to How question

History of evolutionary thought: Darwin's Century

The Darwinian Revolution

     Charles Darwin (1809 - 1882)
            BA, MA (Cambridge)
            Naturalist on board HMS Beagle (1831-36) over father's objections
                Capt. Robert FitzRoy, RN
                South America: extinction real
                Galapagos Islands: variation real
               "The Voyage of the Beagle" (1839): a best-seller

             Examined collections closely:
                    Transmutations in time & space real (March 1837)
                    John Gould sorts out Darwin's Rhea & Finches
                    Joseph Hooker (1817 - 1911) & Asa Gray (1810 - 1888) supply botanical examples

             Read Robert Malthus "On Population" (Sept - Oct 1838):
                    population increases exponentially, resources increase arithmetically
             Extensive study of Artificial Selection by plant & animal breeders

             Married Emma Wedgwood (Jan 1839)
                   Materialism: "I deserve to be called a theist" ;
                   Death of Annie Darwin (1841 - 1851)

             Sketches of 1842 & 1844: "Natural means of selection" / "Picking"
                    "It is like confessing a murder."

            Letter from Alfred Wallace (1823 - 1913) arrives April 1858  [BBC film]
                 Papers read jointly to Linnean Society, July 1858
                HOMEWORK: Compare Wallace letter of 1858 and Darwin sketch of 1842:
                                        is the former an 'abstract' of the latter?
                "On the Origin of Species" (1859) in 11 months [online text]

The theory of evolution by natural selection
        ("Origin", Chapter 4,  pp. 80 - 81)

Observation: In any species, more young are born than can possibly survive.

Observation: Yet a species' numbers do not increase without limit.

CONCLUSION: There is a Struggle for Survival,
        and differential survival & reproduction occur within species.
        [Darwin: "I use 'struggle' in a large and metaphorical sense..."].

Observation: Individuals within species show variation
          that affects likelihood that they will survive this struggle and leave offspring

CONCLUSION: Individuals that survive & reproduce do so in consequence
      of their "adaptively superior" variation (they are "more fit")
      Call this process Natural Selection:
              differential survival & reproduction according to fitness

Observation: Variation is heritable: offspring tend to resemble their parents.
        ["Hard inheritance" is sufficient: Mendel & genetics unknown in 1859).

CONCLUSION:
       Adaptively superior variation will be inherited by the offspring generation.
      That is, evolution occurs as descent with modification.

To put it another way....

      "Natural Selection" describes evolutionary process in which
            "adaptation" occurs in such a way that "fitness" increases.
            Under certain conditions, this results in descent with modification.

      If:     variation exists for some trait, and
                a fitness difference is correlated with that trait, and
                trait is to some degree heritable (determined by genetics),
      Then: trait distribution will change
                over the life history of a species in a single generation,
                    and between generations.

      The process of change is called "adaptation"
                (adaptation both noun & verb)

       That's all.

Implications of Darwin's Theory

     Natural Selection provided a mechanism for Evolution:
                Natural (material) versus super-natural explanation
            Modern evolutionary theory seeks to clarify this mechanism.

      Observable order in Nature due to descent from common ancestor:
            Resemblance due to relationship, not v.v. (cf. Linnaeus)

      Degree of relationship provides a basis for "natural classification":
            Systematic Taxonomy should reflect the phylogeny of organisms.

     All living things are related: Basic fact of biology
       Humans evolved from other animals (Darwin (1871), "Descent of Man")
               "The main conclusion arrived at in this work,
                  namely that man is descended from some lowly organised form,
                  will, I regret to think, be highly distasteful to many."
       Thomas Huxley (1825 - 1895) "Man's Place in Nature" (1863)
                 Established similarity & relationship to Great Apes
                 Bulldog Bests Bishop: Oxford debate (1860)
        Asa Gray (1810 - 1888) (Harvard) applies Darwinian theory to North American plants
        William Dawson (1820 - 1899) (Redpath Museum, McGill U) not so much
             cf. Louis Agassiz (1807 - 1873) at Harvard

    "Nothing in Biology makes sense, except in the light of Evolution." (Th. Dobzhansky, 1975)

PROBLEMS: Evolution by Natural Selection falsifiable from two lines of argument
                      [Falsifiability as criterion of scientific demarcation: see Karl Popper]

   Age of the Earth
         Lyell & Darwin rely on Uniformitarianism: “No vestige of beginning, no sign of end”
         William Thomson (1st Lord Kelvin) calculates age of cooling spheres
               Known processes provide 300 MYR window for life of Sun
               Earth habitable not more than 20 ~ 40 MYR old: insufficient time
                    Cf: HG Wells “Time Machine” (1895)
                          Speciation by 802,701 CE: Eloi vs Morlocks
                          Fast-forward to dying Earth with fading Sun 30 MYR
           Radioactivity (1903) releases terrestrial heat
           Nuclear Fusion (1930s) explains Sun
 
     Mechanism of Inheritance
          Darwin relies on simple “hard” genetics (not soft Lamarckism): offspring resemble parents
          Fleming Jenkin (1867) argues “blending inheritance” logically incompatible with Selection
               White man on a cannibal isle: Politically correct “Purple People Eaters”
          Gregor Mendel (1867) demonstrates “particulate inheritance”
               Purple People Eaters as Green & Yellow Peas
               Ignored until 1900

    Darwinism in disrepute:
            cf. V Kellogg, "Darwinism To-Day" (1907): Alternatives to Natural Selection
            Vitalism
                    Henri Bergson (1907), Creative Evolution (Nobel prize, 1927)
                            "Elan Vital" vs "Elan Locomotif"
                    Teilhard de Chardin (1955), The Phenomenon of Man
                            Evolution teleological: "Omega Point"
             Neo-Lamarckism
                    Pangenesis via gemmules
             Orthogenesis: evolution proceeds in linear sequence and (or) "goal-directed"
                    Morphological evolution continues past "adaptiveness"
            Continuous versus Discrete variation:
                    R Goldschmidt (1940), Material Basis of Evolution: "Hopeful Monsters"

Text material © 2022 by Steven M. Carr