<1800: Evolution accepted
as historical fact:
what is it's explanation ?
The Darwinian Revolution
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 ...." [S&R 9.1]
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]
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..."].
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
"Hard inheritance" sufficient: Mendelian genetics unknown in 1859
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)
exists for some trait, &
fitness difference correlated with trait, &
trait is 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"
Selection provides mechanism for Evolution:
Modern evolutionary theory seeks to clarify mechanism.
Observable order in Nature due to common descent from
Organisms resemble each other because they are related
of relationship provides a basis for "natural
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)
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
Text material © 2022 by Steven M. Carr