Evolution accepted
as historical fact: what is it's 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)
Read Robert Malthus "On Population" (Sept - Oct
1838):
population increases 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 possibly survive.
Observation: Yet species' numbers do not increase without limit.
CONCLUSION: 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 tendency to survive and leave offspring.
CONCLUSION: Those 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: Mendel and genetics unknown in
1859
CONCLUSION:
Superior adaptive
variation will be passed on to offspring generation.
Evolution occurs as descent with modification.
Putting it another way....
"Natural Selection"
describes evolutionary process in which
"adaptation" occurs such that "fitness" increases.
Under certain conditions, this results in descent with
modification.
If:
variation
exists for some trait, and
fitness difference correlated
with trait, and
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"
That's all.
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
Darwin (1837) "I think ...." [S&R
9.1]
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 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
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 © 2019 by Steven M. Carr