By 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
Studied 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..."].
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 an evolutionary process in which
"adaptation" occurs such that population "fitness"
increases.
This results in descent with modification (under certain
conditions)
If:
variation
exists for some trait, &
differential
fitness correlated with
trait, &
trait heritable (offspring resemble
parents),
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
Pattern
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)
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 © 2025 by Steven M. Carr