The Rhetorical Structure of Darwin's Origin of Species
by John Angus Campbell
University of Memphis
Darwin faced a steep persuasive challenge in his masterwork the
Origin of Species. As his notebooks (1837-1839) amply show, from the
earliest stages of his theorizing Darwin thought long and hard about the
problem of persuasion. The Origin can usefully be sectioned into five parts: 1)
The introduction explains how he came upon his theory and previews its
structure; 2) The first four chapters explain the elements of his theory:
selection, variation, competition and the resulting differential adaptation; 3)
A fifth chapter explains inheritance; 4) chapters 6-13 comprise the bulk of the
book and simultaneously rebut objections and confirm Darwin's case; and 5)
chapter fourteen summarizes his argument. With a little leeway for chapter five
the Origin roughly follows the five part pattern of a classical
oration with an exordiam, to place the judge in a favorable state of
mind, a narration, to give the background necessary to the argument; a
confirmation/refutation designed respectively to support one's thesis
and rebut one's opponents' (the order of these elements being variable and may
be intermixed as circumstances require) and a peroration to summarize
the argument and drive it home.
M.J.S. Hodge has argued that, though the pattern is clearer in Darwin's 1842
Sketch and 1844 Essay–the earliest drafts of what became the
Origin–Darwin's masterwork follows the vera causa (hereafter
vc) logic established by Newton and restated by John Herschel in his
Preliminary Discourse (1830). According to the vc principle to
establish a "true cause"–and this is what Darwin wished to do with natural
selection–one must show three things, that: 1) the cause exists independently
of the phenomenon in question; 2) the cause has the competence to bring about
the effect; 3) the cause is responsible for the effect. Though the elements are
not sharply delineated one can see the vc pattern in the chapter divisions of
the Origin. The first chapter "Variation Under Domestication"
establishes the existence of selection separately from nature in the practices
of the domestic breeder. The second and third chapters establish variation and
struggle for existence as active in nature. The fourth chapter, aided by the
material on inheritance in the fifth, argues that the cause is capable of
producing descendants modified from their parents. The remainder of the book
argues that it is more plausible to accept natural selection as the true cause
of species variation, diversity, and divergence than the received theory which
offers no proper material explanation.
As even this brief sketch indicates Darwin's task is not just to convince
his reader's of what we call "evolution." The concept Darwin called "descent
with modification" had been known since antiquity, was advocated by his
grandfather Erasmus (Zoonomia, 1794-96), by the French Scientist
Lamarck (Philosophie zoologic, 1809) and known to the larger public
partly through Charles Lyell's refutation of it in the second volume of his
Principles of Geology (1831-33). Most literate mid-Victorians,
(including Florence Nightingale and Abraham Lincoln) knew of evolution not
through these technical sources but through the Vestiges of the Natural
History of Creation, an overnight sensation published anonymously in 1844
by the Scottish publicist Robert Chambers. Darwin, however, was arguing not
just that species changed over time but that natural selection and sexual
selection–with a variable dose of other factors such as the inheritance of
acquired characteristics–offered a scientific explanation of how it
occurred.
Considered in relation to our ordinary expectations of scientific exposition
it is evident that the Origin, even in its most demanding sections
(for instance the middle of chapter four), is rhetorical in a sense more
popular than professional. For starters the book is written in colloquial
language, is only occasionally abstract, is often highly figurative and is
hardly value free. Consider the title On the Origin of Species by Means of
Natural Selection, or the Preservation of The Favored Races in the Struggle for
Life. The very term "selection" implying as it does consciousness is a
personification; "favored races" sounds uncomfortably close to racism to
post-modern ears; and "struggle for life" sounds like war, competitive sport or
both. One must bear in mind that there were few "professional" scientists in
Darwin's day, that by today's standards Darwin himself was an amateur. The very
word "scientist" was coined by Darwin's Cambridge mentor William Whewell in
1840. (Philosophy of the Inductive Sciences, Vol. 1, p. 113)
It cannot be stressed too strongly that the background to the
Origin is natural theology–the belief that the universe manifests the
kind of order one would expect from mind rather than from material
self-sufficiency. The Origin first invokes this tradition on its
fly-leaf in a citation from William Whewell (Bridgewater Treatise,
1833) A second citation is from Francis Bacon's Advancement of
Learning (1605) urging readers to be versed equally in the Bible and in
philosophy. A third citation from Butler's Analogy of Religion (1736)
distinguishes natural law from miracle on the basis of speed and regularity of
occurrence. This final citation was added in the Origin's third
edition as was a notice of Asa Gray's pamphlet, following the table of
contents, and which Darwin financially underwrote, reconciling natural
selection with natural theology. In these opening examples, as throughout the
book, Darwin takes pains to urge that explaining via "secondary" causes is no
more impious in biology than in physics, geology or chemistry.
But how is Darwin to make good on his claim that natural law can produce the
"contrivances" that we associate with intelligent agency? St. Augustine,
himself no mean rhetorician, observed that no one believes a thing without
first regarding it as believable. An excellent example of this principle is
provided by the first four chapters of the Origin: 1) "Variation Under
Domestication;"2) "Variation Under Nature;" 3) "Struggle for Existence;" and 4)
"Natural Selection." Together these chapters provide a suasory stair-step
leading from the familiar to the unfamiliar–from the unquestionable to the
debatable. The psychological key to Darwin's persuasive effort is to enable his
reader, before any of the truly technical parts of his argument have begun, to
locate the possibility of accepting his views through a series of premises both
familiar and relatively uncontroversial. While Darwin could have illustrated
his first chapter with exotic plants and animals, in effect, he takes the
reader to a British farm. Mixing patriotic celebration of the skill of animal
breeders and nurseryworkers with detailed examples of their work Darwin shows
that domestic plants and animals are often far removed from or have few close
equivalents in nature. He stresses that the difference is owed to the skill of
the breeder, practiced methodically over generations. With his observation that
what his countrymen and other Europeans have raised to high art was practiced
unconsciously from time immemorial by "savages" who favored their best animals
and plants without much thought, Darwin has positioned himself to explain how
mindless processes can produce consequences that seem designed.
Chapter two argues that even as domestic breeding rests on naturally
occurring variation, variation in nature is similarly ubiquitous. Darwin notes
that so persistent is variation in nature that distinguished taxonomists often
cannot agree where a variety leaves off and a species begins. Using an
industrial analogy Darwin urges that since the largest genera have the most
species a large genus may be regarded as a "manufactory" (p.56) of species. He
also changes the meaning "variety" and "species" by redefining a "species" as a
"more or less permanent variety" and a variety as "an incipient species." (pp.
51-54)
Chapter three, "Struggle for Existence," presents Darwin's exposition
of Malthus, and is one of the hardest sells of the book. On Darwin's success in
locating its thesis in the experiential repertoire of his reader rests the
possibility of the reader making the transition between seeing organisms as the
product of mindfulness to the result of unguided material processes. After a
host of intriguing examples from nature and domestication Darwin ends the
chapter asking the reader to imagine what kind of variation would be required
to extend a plant beyond its known range. Having rehearsed a number of
suggestions from the chapter Darwin concludes that the result of this thought
experiment should teach us how little we know of variation and inheritance.
Darwin's confession of ignorance might equally be read as a summation of his
thesis. Given the quantity of Darwin's examples, to say nothing of the charm of
his exposition, a reader who began the chapter with no idea how biological
novelty might have originated ends with abundant clues.
Chapter four, "Natural Selection," which Darwin called "the keystone of my
arch" develops the maxim that whatever man can do nature can do better. The key
passage, one of the most colorful and celebrated of the Origin, is
Darwin's famous personification "natural selection is daily and hourly
scrutinizing, throughout the world, every variation, even the slightest;
rejecting that which is bad, preserving and adding up all that is good…." (p.
84) In this description natural selection can be read two ways. If one reads
his personification as purely figurative one can see that Darwin is describing
an undirected process based partly on natural occurring variation, changing
environmental conditions, Malthus' laws of population, heredity and
unimaginable reaches of time. Read another way Darwin's figure suggests, as
some readers mistakenly inferred, a force (a divine hand?) guiding the process
by a wisdom greater than human. However one reads it the complex figure brings
together what the reader has learned of the breeder operating under
domestication and what is known of nature's own operations. In various passages
Darwin tries to turn the traditional association of science with natural
theology to his own advantage. In chapter five Darwin characterizes special
creation as making "the works of God a mere mockery and deception." (p. 167) In
the final chapter he affirms "There is grandeur in this view of life with its
several powers having been originally breathed into a few forms or into one…."
(p. 490) In the third edition he added "breathed by the Creator." Though Darwin
admits to having "truckled" to "penteteuchal language" in this final section,
aside from a Cheshire cat-like grin hovering over an occasional passage the
argument from design has vanished from Darwin's world.
Though space precludes further elaboration the main elements of Darwin's
persuasive appeal are already in place by the end of the opening pages of the
Origin's fourth chapter. In the body of the work when the going gets
difficult–and to Darwin's everlasting credit he includes in his work every
objection he could think of–Darwin characteristically appeals to the example of
the breeder to convince his reader that the work he requires of natural
selection is conceivable, possible or likely. Given the tremendous achievements
of the domestic breeder–in but a few hundred years–and considering the
omnipotent scope of nature and the enormous time at its disposal–Darwin
repeatedly urges his reader to consider what might not nature have achieved on
its own? Well before the end of the Origin, if not every reader, then
at least for the minority who would carry forward Darwin's legacy–the question
was no longer rhetorical.
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BIOSKETCH
John Angus Campbell is a Senior Affiliate Faculty at the University of
Memphis. Until his recent retirement he was Professor and Graduate Program
Director in the Department of Communication. He is a past president and current
second vice president of the American Association for the Rhetoric of Science
and Technology and one of the founders of the rhetoric of science as an
academic subdiscipline. With Stephen C. Meyer he is co-editor/author of
Darwin, Design and American Public Education, published by Michigan
State University Press. He has written numerous essays and book chapters on the
strategy and structure of Darwin's Origin.