Darwin, Wallace & The Origin of Species.
I.
Origin of The Origin.
A. Published in 1859.
B. The result of a year’s furious writing.
1. Darwin had opened his first “Transmutation” notebook
upon his return to England in 1836.
2. Continued to work on the “species problem” in almost
complete secrecy for the next 20+ years.
3. Evolution of his thoughts chronicled in a series of notebooks:
a. Last part of the “Red Notebook” begun while he was
still aboard HMS Beagle.
b. The “Transmutation” Notebooks (a-d).
c. The 1842 “Sketch.”
d. The 1844 “Essay,” partly reprinted in the DarwinWallace “paper.”
4. “Natural selection” first appears in the 4th Transmutation notebook written in 1839.
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5. Gist of The Origin appears in the “Sketch” and then, in
fuller form, in the “Essay.”
6. For recent review of the evolution of Darwin’s thinking,
see Eldredge (2005 PLOS Biology).
C. From 1844-1858, Darwin devoted himself principally to
other tasks even while continuing to amass evidence to be
included in his “Great Species Book.”
D. In 1858, he received Wallace’s famous manuscript and a
letter asking Darwin to forward it to Lyell for publication "if
Mr. Darwin thought it sufficiently novel and interesting."
1. Wallace had previously (1855) published a paper in which
he asserted that "Every species has come into existence
coincident both in time and space with a pre-existing
closely allied species."
2. Now, he identified the mechanism, natural selection, responsible for progressive change.
3. Darwin dithered, consulted with his friends.
4. Result was the joint “paper” communicated to the Linnean Society by Hooker and Lyell in 1858.
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E. A year later, The Origin was published.
1. The first edition of 1500 copies sold out in a day.
2. A third were purchased by Mudie’s Circulating Library.
3. From his retreat at Down, Darwin embarked on a public
relations campaign, corresponding with and sending
copies of The Origin to friends and colleagues the world
over.
4. The Origin was widely reviewed, Darwin’s supporters,
especially T. H. Huxley, engaged in numerous exchanges
with opponents including the famous of which was the
debate with Bishop Wilberforce.
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Darwin’s Predecessors.
A. Lamarck is the most famous – being widely associated with
what is now regarded as the “heresy” of the inheritance of
acquired characters.
1. Others included Buffon, Erasmus Darwin and Robert
Chambers.
2. Of these, Chambers was the most influential in laying the
groundwork for public acceptance of The Origin.
3. Surprisingly, the idea of natural selection had been anticipated by both Hutton (Pearson, 2003) and Paley (Abler,
2003).
B. Scientific wisdom that Darwin went up against was Special
Creation & Fixity of Species.
1. Legacy of Cuvier who argued for
a. Fixity of species over historical, and, by inference,
over geological, time.
b. Lack of relation between extinct and living forms.
c. Successive creation of whole floras and faunas and
their wholesale extinction (revolutionary upheavals).
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2. As espoused by Lyell:
a. Retained fixity of species.
b. Replaced catastrophism
with uniformitarian extinction and species’
creation.
C. Uniformitarianism: Lyell used
the word in different ways.
1. Gould distinguishes:
a. Uniformity of law;
b. Uniformity of process – “actual” causes;
c. Uniformity of rate – gradualism;
d. Uniformity of state – non-progressionism.
2. “a” and “b” generally accepted methodological postulates:
a. To understand the past we assume physical law and
observable process then as now.
b. Law more universal than process.
3. “c” and “d” are assumptions regarding earth’s history.
D. Non-progressionism especially – a response to Lamarck –
led to absurdity:
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“Then might those genera of animals return, of which the memorials are preserved in the ancient rocks of our continents. The huge
Iguanodon might reappear in the woods, and the ichthyosaur in
the sea, while the pterodactyle [sic] might flit again through umbrageous groves of tree-ferns.” – Principles of Geology, Vol. I.
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III. The Triumph of Darwinism.
A. Offered an economical explanation of numerous, distributional, anatomical and developmental observations –
Darwin’s “facts.”
"During the voyage of the Beagle I had been deeply impressed by
discovering in the Pampean formation great fossil animals covered with armour like that on the existing armadillos; secondly, by
the manner in which closely allied animals replace one another in
proceeding southwards over the Continent; and thirdly, by the
South American character of most of the productions of the Galapagos archipelago, and more especially by the manner in which
they differ slightly on each island of the group; none of the islands
appearing to be very ancient in a geological sense.”
“It was evident that such facts as these, as well as many others,
could only be explained on the supposition that species gradually
become modified … ." – Autobiographgy.
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B. Darwin compared his labors to
those of 17th century astronomers who established the reality of the heliocentric solar system.
C. Some important elements of
Darwinism:
1. Posited near-limitless time
for species to evolve by imperceptible steps – species
from varieties; genera from
species, etc.
2. Essentially a theory of competition.
3. Blending inheritance assumed.
4. Role of chance not thought
through.
D. In studying the “evolution of
evolution,” important to distinguish:
1. Descent with modification;
2. Mechanism that produces
it.
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IV. Darwin vs. Lamarck.
A. Lamarck was led to the idea
of evolution by two principle
observations.
1. Species grade into each
other;
2. Increased sophistication of
design as one goes from
monad to man.
B. Lamarck rejected extinction
of entire species.
1. Nature wouldn’t allow it.
2. Save possibly in the case
of extermination by man.
C. Lamarck Posited
1. Inherent tendency toward progress – “Power of Life;”
2. Local adaptation mediated by use and disuse – a consequence of organismal “need” (besoins).
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D. Darwin also allowed for use and disuse and for environmental effects.
1. Subsidiary to natural selection which winnowed the (heritable) variation thereby engendered.
2. Viewed evolutionary “progress” as a consequence of
natural selection.
3. From the 6th edition of The Origin:
“If we take as the standard of high organisation, the amount of differentiation and specialisation of the several organs … , natural selection clearly leads towards this standard: for all physiologists admit
that the specialisation of organs … is an advantage to each being; …
.”
4. Conversely, the continued existence of primitive forms reflected a lack of advantage accruing to increased complexity:
“But it may be objected that if all organic beings thus tend to rise in
the scale, how is it that throughout the world a multitude of the lowest
forms still exist …? .... On our theory the continued existence of lowly
organisms offers no difficulty; for natural selection … does not necessarily include progressive development—it only takes advantage of
such variations as arise and are beneficial to each creature under its
complex relations of life.” [The Origin – 6th edition]
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V. Demise of Darwinism.
A. Jenkins – loss of favorable variations due to
1. Chance.
2. Blending.
B. Lord Kelvin – Jenkins’ colleague – calculated the age of the
earth to be 20 million years.
C. The problem became to generate variation in sufficient
quantity for life to evolve in the allotted time.
D. Darwin now
1. Increasingly relied upon rapid environmental to synchronize the appearance of “parallel” variation.
2. Invented “pangenesis” to make heritable individual response to environmental influences.
3. Recognized Huxley’s assertion that “biology took her
time from geology” for the evasion it was.
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VI. The Modern Synthesis.
A. Rediscovery of particulate inheritance (Mendel) provided
the answer to Jenkin.
B. Discovery of radioactive decay and thermonuclear fusion
answered Kelvin.
C. Modern synthesis represented
fusion of genetics, paleontology
and evolution.
1. Critical realization was the
fact that “continuous variation” of metric traits could be
accounted for my polygenic
inheritance.
2. Assumed independence of germ plasm and soma.
3. “Stuff” of evolution held to be small scale variations.
4. Conditions of life enter only through natural selection.
5. Orthogenesis debunked.
6. Gene frequencies affected by a variety of forces, but
natural selection the only creative force..
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VII. Recent Developments.
A. Punctuated Equilibrium – questions evolutionary uniformity of rate.
B. Evo-Devo – questions uniformity of variation magnitude.
C. Epigenetics – questions germ-soma independence.