Darwin's Century

Charles Darwin & the Origins of Natural Selection
What is Natural Selection & how does it work?
How does Natural Selection explain Evolution

<1800: Evolution accepted as historical fact: what is its explanation ?

The Darwinian Revolution

     Charles Darwin (1809 -1882)
            Naturalist on board HMS Beagle (1831-36)
                South America: extinction real
                Galapagos Islands: variation real
           "The Voyage of the Beagle" (1839): best-seller

             Examined collections closely:
                    transmutations in time & space real (March 1837): "I think ...."
             Read R Malthus "On Population" (Sept - Oct 1838):
                    populations increase exponentially, resources increase arithmetically
             Extensive study of artificial selection by plant & animal breeders

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

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

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

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

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

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

Observation: Individuals within species show variation
that affects tendency to survive & leave offspring

CONCLUSION: Individuals that survive and reproduce do so in consequence
of "superior adaptive variation" (they are "more fit")
Process of differential survival & reproduction described as Natural Selection.

Observation: Variation heritable: offspring tend to resemble parents
"Hard inheritance" sufficient: Mendelian genetics unknown in 1859

CONCLUSION:
Superior adaptive variation will be transmitted to offspring generation
Evolution occurs as descent with modification

Put another way....

      "Natural Selection" names & describes an evolutionary phenomenon in which
            "adaptation" occurs such that "fitness" increases.
            This results in descent with modification (under certain conditions)

      If:     variation exists for some trait, &
              fitness difference correlated with trait, &
              trait heritable (determined by genetics),
      Then: trait distribution will change
                over life history of organisms in any single generation,
                    and between generations.

Process of change called "adaptation"

That's all.

Implications of Darwin's Theory

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

Observable order in Nature due to common descent from common ancestor:
Organisms resemble each other because they are related

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

     All living things are related (the basic fact of Biology):
       Humans evolved from simian ancestors (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 structural similarity & relationship to Great Apes

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

For further reading:

   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 Eiseley (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.
    Gordon Ratray Taylor (1963). The Science of Life. McGraw-Hill.
    Biology 4270 - History of Biology

Web resources:
    John van Wyhe (ed.), The writings of Charles Darwin on the web
                                       (http://pages.britishlibrary.net/charles.darwin/)
                                        Darwin biography [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