I summon the supernatural beings
Who first contrived
The transmorgifications
In the stuff of life.
You did it for your own amusement.
Descend again, be pleased to reanimante
This revival of those marvels.
Reveal, now, exactly
How they were performed
From the beginning
Up to this moment.
                                        Ovid: Metamorphoses
                                            (trans. Ted Hughes)

Biology in the 18th century
     The Classical Tradition: Plato & Aristotle (4th cent. BCE)
       Theory of Forms (essences, eidos)
                  'real' objects are manifestations of 'ideal' forms
                  variation is illusory  [see Plato "The Republic"]
       Dichotomy: the world is composed of paired opposites
                  "A" versus "not A" classes
                  good / bad, right / wrong, up / down, light / dark, male / female, etc.
           e.g., vertebrates vs. invertebrates
       Aristotle - "Father of Biology"
                Five books on zoology ("Generation of Animals")
                Biological structures have purpose: Efficient versus Final Causes

     Natural Theology:
            "The Wisdom of God, Manifested in His Creation" (John Ray 1627-1705)
                  'Ideal' forms exist in the Mind of God:
                  'real' world created by God (Genesis 1:1)
            "Natural Theology" (1802) (William Paley)
                   The Argument from Design: a watch presupposes a Watchmaker
            Scala Naturae: the "Great Chain of Being"
                  Creation is an infinitely graduated progressive series
                  Time scale is short (ca. 6,000 years)
                  Living forms are static: no new forms, no change, no extinction
            The study of nature is a pious activity

     Linnean Taxonomy (Carl von Linne [Carolus Linneaus] 1707 -1778)
            "Systema Naturae" (10th ed., 01 January 1758: "Birthday of Systematics")
                  4,162 animals described
            binomial nomenclature: genus + species names
                  "ad majorem Dei gloriam": for the greater glory of God

     Exploration creates a Scientific Crisis
       New forms are discovered that don't fit the Scala
       Extinctions have evidently occurred
       Variation is real in space: what about over time?

Biology in the early 19th century:
      Change has occurred, how do we explain it?
     The Enlightenment favors rational explanation.

     Jean Baptiste de Lamarck (1744 -1829): "Zoological Philosophy" (1809)
            New features arise due to persistent "besoin" (need / want)
                  (teleological: a goal-directed explanation)
            Use and disuse alter morphology:
            Altered morphology is passed on to offspring
                  (Lamarckism: inheritance of acquired characteristics)
             Ex.: Giraffes stretch their necks to feed on leaves.
                           Successive generations gradually acquire longer necks.
                            [or, trees become taller to escape giraffes]
            Therefore, organisms change (evolve) over time

     Uniformitarianism replaces Catastrophism in geology
       Charles Lyell (1797 -1875): "Principles of Geology" (1830)
       Observable, gradual processes + enormous time = world as we know it

The Darwinian Revolution

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

             Examined collections closely:
                    transmutations in time & space are real (March 1837)
             Read Robert Malthus "On Population" (Sept - Oct 1838):
                    population increases exponentially, resources increase arithmetically
             Extensive study of Artifical Selection by  plant & animal breeders

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

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

            Letter from Alfred Wallace (1823-1913) in June 1858
                "On the Origin of Species" (1859) [online text]

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 and reproduction occur within species.
        [Darwin: "I use 'struggle' in a large and metaphorical sense..."].

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

CONCLUSION: Those individuals that survive and reproduce do so in consequence
      of their "adaptively superior" variation (they are "more fit")
      This process of differential survival and reproduction is called Natural Selection.

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

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

Putting it another way....

      "Natural Selection" describes an 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
                the trait is to some degree heritable (determined by genetics),
      Then: the trait distribution will change
                over the life history of organisms in a single generation,
                    and between generations.

      The process of change is called "adaptation"

       That's all.

     Natural Selection provides a mechanism for Evolution:
            Modern evolutionary theory seeks to clarify this mechanism.

      The observable order in Nature is due to common descent from an ancestor:
            Organisms resemble each other because they are related.

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

     All living things are related (the basic fact of biology):
       Humans have 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 and relationship to Great Apes

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

Natural Selection may be the most misunderstood concept in biology.

Not "Survival of the Fittest"
      Herbert Spencer (1820 - 1903) "Synthetic Philosophy"
            Phrase introduced in 1864, advocated by Wallace, accepted by Darwin
            the "naturalistic fallacy": 'is'  = 'ought'
            Social Darwinism: Does "Survival of the Fittest" support
                British imperial ambition
                American laissez faire capitalism
                Negative Eugenics ?
            "A deduction killed by a fact" [T.  H. Huxley]

      not phenotype-specific mortality
      not predation (nor inter-species competition of unrelated species)
      not  "Nature red in tooth and claw"
           Darwin: plants in desert 'struggle' for water
      not equivalent to population growth:
           evolving populations may decline: density-dependent growth in Atlantic Cod

Not equivalent to evolution
      Natural Selection may conserve existing types (stabilizing selection).
      Evolutionary change ultimately requires new variation (mutation & recombination).
      Paradox: Natural Selection may or may not explain the "Origin of Species"
          Migration, population structure, genetic drift are important.

Not a tautology (a self-evident statement; a circular argument)
      "Why do they survive? Cuz they're fit.
            How do you know they're fit? Cuz they survive..."etc.

      More like a syllogism (an if - then statement; a logical consequence):
            (² & W  &  h²) => q
            [cf. physics:  F = M A  depending on definitions of Force, Mass, & Acceleration
                 arithmetic:  1 + 2 = 3  because I and II make III]

      The process can be represented in non-deterministic genetic models
             variation, fitness, and heritability are all quantifiable in nature

       Falsifiability as a demarcator of Science (Karl Popper)
             Fleming Jenkin on blending inheritance: cf. Darwin's theory of pangenesis
             Lord Kelvin on the Age of the Earth: insufficient time (with nuclear solar energy)

Not "Mother Nature"
      not a force, not a thing that acts
           We don't say, "Arithmetic causes one plus two to equal three."
            We might say, "One plus two equals three. That's arithmetic.
      not good or bad (amoral)

      no noun / verb / object distinctions
            In most languages, "nouns verb objects"
                i.e., objects perform actions on other objects: Not

Not  teleological (goal-directed):

      Evolution does not have "goal", "direction", or "purpose"
            Homo sapiens are not the endpoint of evolution!

       Evolution is not necessarily "progressive"
             variation & "complexity" do not increase uniformly

      Avoid such phrases as "Natural Selection acts ..."
           "in order to ...",
           "for the purpose of ...",
           "so that ...",
           "because its trying to ..."

   Janet Browne (1995). Charles Darwin: Voyaging. Knopf
                            (2002). Charles Darwin: The Power of Place. Knopf.
    Daniel C. Dennet (1995). Darwin's Dangerous Idea. Beacon                                              
    Loren Eisley (1959). Darwin's Century. Doubleday.
    Stephen Jay Gould (2002). The Structure of Evolutionary Theory. Harvard.
    Richard Hofstader (1955). Social Darwinism in American Thought, 1860 -1915 (rev. ed.). Beacon.
    William Irvine (1955). Apes, Angels, and Victorians: Darwin, Huxley, & Evolution. McGraw-Hill.
    Ernst Mayr (1994). One Long Argument [see especially Chapter 4: Darwin's Path]. Harvard University Press.

Web resouces:
    John van Wyhe (ed.), The writings of Charles Darwin on the web (http://pages.britishlibrary.net/charles.darwin/)
    Brief biography of Darwin by John van Wyhe [http://pages.britishlibrary.net/charles.darwin3/darwin_bio.htm]
    Course notes for Bio2900 - Principles of Evolution & Systematics
    Extract from PBS special "Darwin's Dangerous Idea": Natural Selection in 10 minutes