Sir Isaac Newton, among other leaders in the scientific revolution, including René Descartes,
upheld "that the physical laws he had uncovered revealed the mechanical
perfection of the workings of the universe to be akin to a watch,
wherein the watchmaker is God."
The 1859 publication of Charles Darwin's theory of natural selection put forward an explanation for complexity and adaptation, which reflects scientific consensus on the origins of biological diversity. This provides a counter-argument to the watchmaker analogy: for example, the evolutionary biologistRichard Dawkins referred to the analogy in his 1986 book The Blind Watchmaker giving his explanation of evolution. Others, however, consider the watchmaker analogy to be compatible with evolutionary creation, opining that the two concepts are not mutually exclusive. In the 19th century, deists, who championed the watchmaker analogy, held that Darwin's theory fit with "the principle of uniformitarianism—the idea that all processes in the world occur now as they have in the past" and that deistic evolution "provided an explanatory framework for understanding species variation in a mechanical universe."
The scientific revolution
"nurtured a growing awareness" that "there were universal laws of
nature at work that ordered the movement of the world and its parts." Amos Yong
writes that in "astronomy, the Copernican revolution regarding the
heliocentrism of the solar system, Johannes Kepler's (1571–1630) three
laws of planetary motion, and Isaac Newton's (1642–1727) law of
universal gravitation—laws of gravitation and of motion, and notions of
absolute space and time—all combined to establish the regularities of
heavenly and earthly bodies".
Simultaneously, the development of machine technology and the emergence of the mechanical philosophy
encouraged mechanical imagery unlikely to have come to the fore in previous ages.
With such a backdrop, "deists suggested the watchmaker analogy: just as
watches are set in motion by watchmakers, after which they operate
according to their pre-established mechanisms, so also was the world
begun by the God as creator, after which it and all its parts have
operated according to their pre-established natural laws. With these
laws perfectly in place, events have unfolded according to the
prescribed plan." For Sir Isaac Newton, "the regular motion of the planets made it reasonable to believe in the continued existence of God".
Newton also upheld the idea that "like a watchmaker, God was forced to
intervene in the universe and tinker with the mechanism from time to
time to ensure that it continued operating in good working order".
Similar to Newton, René Descartes
(1596–1650) speculated on "the cosmos as a great time machine operating
according to fixed laws, a watch created and wound up by the great
watchmaker".
William Paley
Watches and timepieces have been used as examples of complicated technology in philosophical discussions. For example, Cicero, Voltaire and René Descartes all used timepieces in arguments regarding purpose. The watchmaker analogy, as described here, was used by Bernard le Bovier de Fontenelle in 1686, but was most famously formulated by Paley.
In crossing a heath, suppose I
pitched my foot against a stone, and were asked how the stone came to be
there; I might possibly answer, that, for anything I knew to the
contrary, it had lain there forever: nor would it perhaps be very easy
to show the absurdity of this answer. But suppose I had found a watch
upon the ground, and it should be inquired how the watch happened to be
in that place; I should hardly think of the answer I had before given,
that for anything I knew, the watch might have always been there. ...
There must have existed, at some time, and at some place or other, an
artificer or artificers, who formed [the watch] for the purpose which we
find it actually to answer; who comprehended its construction, and
designed its use. ... Every indication of contrivance, every
manifestation of design, which existed in the watch, exists in the works
of nature; with the difference, on the side of nature, of being greater
or more, and that in a degree which exceeds all computation.
— William Paley, Natural Theology (1802)
Paley went on to argue that the complex structures of living things
and the remarkable adaptations of plants and animals required an
intelligent designer. He believed the natural world was the creation of
God and showed the nature of the creator. According to Paley, God had
carefully designed "even the most humble and insignificant organisms"
and all of their minute features (such as the wings and antennae of earwigs). He believed, therefore, that God must care even more for humanity.
Paley recognised that there is great suffering in nature and
nature appears to be indifferent to pain. His way of reconciling that
with his belief in a benevolent God was to assume that life had more pleasure than pain.
As a side note, a charge of wholesale plagiarism from this book was brought against Paley in The Athenaeum
for 1848, but the famous illustration of the watch was not peculiar to
Nieuwentyt and had been used by many others before either Paley or
Nieuwentyt. But the charge of plagiarism was based on more similarities.
For example, Niewentyt wrote "in the middle of a Sandy down, or in a
desart {sic} and solitary Place, where few People are used to pass, any
one should find a Watch ..."
Joseph Butler
William Paley taught the works of Joseph Butler
and appears to have built on Butler's 1736 design arguments of
inferring a designer from evidence of design. Butler noted:
"As the manifold Appearances of Design and of final Causes, in the
Constitution of the World, prove it to be the Work of an intelligent
Mind ... The appearances of Design and of final Causes in the constitution of nature as really prove this acting agent to be an intelligent Designer... ten thousand Instances of Design, cannot but prove a Designer.".
Jean-Jacques Rousseau
Rousseau also mentioned the watchmaker theory. He wrote the following in his 1762 book, Emile:
I am like a man who sees the works of a watch for the first time; he is
never weary of admiring the mechanism, though he does not know the use
of the instrument and has never seen its face. I do not know what this
is for, says he, but I see that each part of it is fitted to the rest, I
admire the workman in the details of his work, and I am quite certain
that all these wheels only work together in this fashion for some common
end which I cannot perceive. Let us compare the special ends, the
means, the ordered relations of every kind, then let us listen to the
inner voice of feeling; what healthy mind can reject its evidence?
Unless the eyes are blinded by prejudices, can they fail to see that the
visible order of the universe proclaims a supreme intelligence? What
sophisms must be brought together before we fail to understand the
harmony of existence and the wonderful co-operation of every part for
the maintenance of the rest?
Criticism
David Hume
Before Paley published his book, David Hume
(1711–1776) had already put forward a number of philosophical
criticisms of the watch analogy, and to some extent anticipated the
concept of natural selection. His criticisms can be separated into three major distinctions:
His first objection is that we have no experience of
world-making. Hume highlighted the fact that everything we claim to know
the cause of, we have derived the inductions from previous experiences
of similar objects being created or seen the object itself being created
ourselves. For example, with a watch, we know it has to be created by a
watch-maker because we can observe it being made and compare it to the
making of other similar watches or objects to deduce they have alike
causes in their creation. However, he argues that we have no experience
of the universe's creation or any other universe's creations to compare
our own universe to and never will; therefore, it would be illogical to
infer that our universe has been created by an intelligent designer in
the same way that a watch has.
The second criticism that Hume offers is about the form of the
argument as an analogy in itself. An analogical argument claims that
because object X (a watch) is like object Y (the universe) in one
respect, both are therefore probably alike in another, hidden, respect
(their cause, having to be created by an intelligent designer). He
points out that for an argument from analogy to be successful, the two
things that are being compared have to have an adequate number of
similarities that are relevant to the respect that are analogised. For
example, a kitten and a lion may be very similar in many respects, but
just because a lion makes a "roar", it would not be correct to infer a
kitten also "roars": the similarities between the two objects being not
enough and the degree of relevance to what sound they make being not
relevant enough. Hume then argues that the universe and a watch also do
not have enough relevant or close similarities to infer that they were
both created the same way. For example, the universe is made of organic
natural material, but the watch is made of artificial mechanic
materials. He claims that in the same respect, the universe could be
argued to be more analogous to something more organic such as a
vegetable (which we can observe for ourselves does not need a 'designer'
or a 'watchmaker' to be created). Although he admits the analogy of a
universe to a vegetable to seem ridiculous, he says that it is just as
ridiculous to analogize the universe with a watch.
The third criticism that Hume offers is that even if the argument
did give evidence for a designer; it still gives no evidence for the
traditional 'omnipotent', 'benevolent' (all-powerful and all-loving) God
of traditional Christian theism. One of the main assumptions of Paley's
argument is that 'like effects have like causes'; or that machines
(like the watch) and the universe have similar features of design and so
both also have the same cause of their existence: they must both have
an intelligent designer. However, Hume points out that what Paley does
not comprehend is to what extent 'like causes' extend: how similar the
creation of a universe is to the creation of a watch. Instead, Paley
moves straight to the conclusion that this designer of the universe is
the 'God' he believes in of traditional Christianity. Hume, however
takes the idea of 'like causes' and points out some potential
absurdities in how far the 'likeness' of these causes could extend to if
the argument were taken further as to explain this. One example that he
uses is how a machine or a watch is usually designed by a whole team of
people rather than just one person. Surely, if we are analogizing the
two in this way, it would point to there being a group of gods who
created the universe, not just a single being. Another example he uses
is that complex machines are usually the result of many years of trial
and error with every new machine being an improved version of the last.
Also by analogy of the two, would that not hint that the universe could
also have been just one of many of God's 'trials' and that there are
much better universes out there? However, if that were taken to be true,
surely the 'creator' of it all would not be 'all loving' and 'all
powerful' if they had to carry out the process of 'trial and error' when
creating the universe?
Hume also points out there is still a possibility that the
universe could have been created by random chance but still show
evidence of design as the universe is eternal and would have an infinite
amount of time to be able to form a universe so complex and ordered as
our own. He called that the 'Epicurean hypothesis'. It argued that when
the universe was first created, the universe was random and chaotic, but
if the universe is eternal, over an unlimited period of time, natural
forces could have naturally 'evolved' by random particles coming
together over time into the incredibly ordered system we can observe
today without the need of an intelligent designer as an explanation.
The last objection that he makes draws on the widely discussed problem of evil.
He argues that all the daily unnecessary suffering that goes on
everywhere within the world is yet another factor that pulls away from
the idea that God is an 'omnipotent' 'benevolent' being.
When Darwin completed his studies of theology at Christ's College, Cambridge in 1831, he read Paley's Natural Theology and believed that the work gave rational proof of the existence of God. That was because living beings showed complexity and were exquisitely fitted to their places in a happy world.
Subsequently, on the voyage of the Beagle, Darwin found that nature was not so beneficent, and the distribution of species did not support ideas of divine creation. In 1838, shortly after his return, Darwin conceived his theory that natural selection,
rather than divine design, was the best explanation for gradual change
in populations over many generations. He published the theory in On the Origin of Species in 1859, and in later editions, he noted responses that he had received:
It can hardly be supposed that a
false theory would explain, in so satisfactory a manner as does the
theory of natural selection, the several large classes of facts above
specified. It has recently been objected that this is an unsafe method
of arguing; but it is a method used in judging of the common events of
life, and has often been used by the greatest natural philosophers ...
I see no good reason why the views given in this volume should shock the
religious feelings of any one. It is satisfactory, as showing how
transient such impressions are, to remember that the greatest discovery
ever made by man, namely, the law of the attraction of gravity, was also
attacked by Leibnitz, "as subversive of natural, and inferentially of
revealed, religion." A celebrated author and divine has written to me
that "he has gradually learnt to see that it is just as noble a
conception of the Deity to believe that He created a few original forms
capable of self-development into other and needful forms, as to believe
that He required a fresh act of creation to supply the voids caused by
the action of His laws."
— Charles Darwin, The Origin of Species (1859)
Darwin reviewed the implications of this finding in his autobiography:
Although I did not think much about
the existence of a personal God until a considerably later period of my
life, I will here give the vague conclusions to which I have been
driven. The old argument of design in nature, as given by Paley, which
formerly seemed to me so conclusive, fails, now that the law of natural
selection has been discovered. We can no longer argue that, for
instance, the beautiful hinge of a bivalve shell must have been made by
an intelligent being, like the hinge of a door by man. There seems to be
no more design in the variability of organic beings and in the action
of natural selection, than in the course which the wind blows.
Everything in nature is the result of fixed laws.
— Charles Darwin, The Autobiography of Charles Darwin 1809–1882. With the original omissions restored.
The idea that nature was governed by laws was already common, and in 1833, William Whewell as a proponent of the natural theology
that Paley had inspired had written that "with regard to the material
world, we can at least go so far as this—we can perceive that events are
brought about not by insulated interpositions of Divine power, exerted
in each particular case, but by the establishment of general laws." Darwin, who spoke of the "fixed laws" concurred with Whewell, writing in his second edition of On The Origin of Species:
There is grandeur in this view of
life, with its several powers, having been originally breathed by the
Creator into a few forms or into one; and that, whilst this planet has
gone cycling on according to the fixed law of gravity, from so simple a
beginning endless forms most beautiful and most wonderful have been, and
are being, evolved.
— Charles Darwin, The Origin of Species (1860)
By the time that Darwin published his theory, theologians of liberal Christianity
were already supporting such ideas, and by the late 19th century, their
modernist approach was predominant in theology. In science, evolution theory incorporating Darwin's natural selection became completely accepted.
Richard Dawkins
Richard Dawkins
In The Blind Watchmaker, Richard Dawkins
argues that the watch analogy conflates the complexity that arises from
living organisms that are able to reproduce themselves (and may become
more complex over time) with the complexity of inanimate objects, unable
to pass on any reproductive changes (such as the multitude of parts
manufactured in a watch). The comparison breaks down because of this
important distinction.
In a BBC Horizon episode, also entitled The Blind Watchmaker,
Dawkins described Paley's argument as being "as mistaken as it is
elegant". In both contexts, he saw Paley as having made an incorrect
proposal as to a certain problem's solution, but Dawkins did not
disrespect him. In his essay The Big Bang, Steven Pinker
discusses Dawkins's coverage of Paley's argument, adding: "Biologists
today do not disagree with Paley's laying out of the problem. They
disagree only with his solution."
In his book The God Delusion,
Dawkins argues that life was the result of complex biological
processes. He makes the argument that the comparison to the lucky
construction of a watch is fallacious because proponents of evolution do
not consider evolution "lucky". Rather than luck, the evolution of
human life is the result of billions of years of natural selection. He
concludes that evolution is a fair contestant to replace God in the role
of watchmaker.
In addition, he argues that the watchmaker's creation of the
watch implies that the watchmaker must be more complex than the watch.
Design is top-down, someone or something more complex designs something
less complex.
To follow the line upwards demands that the watch was designed by a
(necessarily more complex) watchmaker, the watchmaker must have been
created by a more complex being than himself. So the question becomes
who designed the designer?
Dawkins argues that (a) this line continues ad infinitum, and (b) it
does not explain anything.
Evolution, on the other hand, takes a bottom-up approach; it
explains how more complexity can arise gradually by building on or
combining lesser complexity.
In response to such claims, Nathan Schneider writes, "Paley died decades before The Origin of Species
was published, and ever since his views have been so repeatedly set in
opposition to Darwin's that Richard Dawkins titled one of his books on
evolution The Blind Watchmaker. A closer look at Paley's own
thinking reveals, however, a God who works through the laws of nature,
not beyond them like the modern ID theorists' designer. Paley had no
objection to species changing over time. It's only in today's highly
polarized culture-war climate that we don't bother to notice that one of
the forefathers of intelligent design theory might have been perfectly
comfortable with evolution."
Richerson and Boyd
Biologist Peter Richerson and anthropologist Robert Boyd
offer an oblique criticism by arguing that watches were not "hopeful
monsters created by single inventors," but were created by watchmakers
building up their skills in a cumulative fashion over time, each
contributing to a watch-making tradition from which any individual
watchmaker draws their designs.
Contemporary usage
In the early 20th century, the modernist theology of higher criticism was contested in the United States by Biblical literalists, who campaigned successfully against the teaching of evolution and began calling themselves creationists in the 1920s. When teaching of evolution was reintroduced into public schools in the 1960s, they adopted what they called creation science that had a central concept of design in similar terms to Paley's argument. That idea was then relabeled intelligent design,
which presents the same analogy as an argument against evolution by
natural selection without explicitly stating that the "intelligent
designer" was God. The argument from the complexity of biological
organisms was now presented as the irreducible complexity argument, the most notable proponent of which was Michael Behe, and, leveraging off the verbiage of information theory, the specified complexity argument, the most notable proponent of which was William Dembski.
The watchmaker analogy was referenced in the 2005 Kitzmiller v. Dover Area School District trial. Throughout the trial, Paley was mentioned several times. The defense's expert witness John Haught noted that both Intelligent Design and the watchmaker analogy are "reformulations" of the same theological argument.
On day 21 of the trial, Mr. Harvey walked Dr. Minnich through a
modernized version of Paley's argument, substituting a cell phone for
the watch.
In his ruling, the judge stated that the use of the argument from design
by intelligent design proponents "is merely a restatement of the
Reverend William Paley's argument applied at the cell level,"
adding "Minnich, Behe, and Paley reach the same conclusion, that
complex organisms must have been designed using the same reasoning,
except that Professors Behe and Minnich refuse to identify the designer,
whereas Paley inferred from the presence of design that it was God."
The judge ruled that such an inductive argument is not accepted as
science because it is unfalsifiable.
Irreducible complexity (IC) is the argument that certain biological systems cannot have evolved by successive small modifications to pre-existing functional systems through natural selection, because no less complex system would function. Irreducible complexity has become central to the creationist concept of intelligent design, but the scientific community, which regards intelligent design as pseudoscience, rejects the concept of irreducible complexity. Irreducible complexity is one of two main arguments used by intelligent-design proponents, alongside specified complexity.
Creation science presented the theological argument from design with assertions that evolution could not explain complex molecular mechanisms, and in 1993 Michael Behe, a professor of biochemistry at Lehigh University, presented these arguments in a revised version of the school textbook Of Pandas and People. In his 1996 book Darwin's Black Box he called this concept irreducible complexity and said it made evolution through natural selection of random mutations impossible.
This was based on the mistaken assumption that evolution relies on
improvement of existing functions, ignoring how complex adaptations
originate from changes in function, and disregarding published research. Evolutionary biologists have published rebuttals showing how systems discussed by Behe can evolve, and examples documented through comparative genomics
show that complex molecular systems are formed by the addition of
components as revealed by different temporal origins of their proteins.
In the 2005 Kitzmiller v. Dover Area School District
trial, Behe gave testimony on the subject of irreducible complexity.
The court found that "Professor Behe's claim for irreducible complexity
has been refuted in peer-reviewed research papers and has been rejected
by the scientific community at large."
Definitions
Michael Behe defined irreducible complexity in natural selection in terms of well-matched parts in his 1996 book Darwin's Black Box:
... a single system which is composed of several
well-matched, interacting parts that contribute to the basic function,
and where the removal of any one of the parts causes the system to
effectively cease functioning.
A second definition given by Behe in 2000 (his "evolutionary definition") states:
An irreducibly complex evolutionary pathway is one that
contains one or more unselected steps (that is, one or more
necessary-but-unselected mutations). The degree of irreducible
complexity is the number of unselected steps in the pathway.
Intelligent-design advocate William A. Dembski assumed an "original function" in his 2002 definition:
A system performing a given basic function is irreducibly
complex if it includes a set of well-matched, mutually interacting,
nonarbitrarily individuated parts such that each part in the set is
indispensable to maintaining the system's basic, and therefore original,
function. The set of these indispensable parts is known as the
irreducible core of the system.
History
Forerunners
The argument from irreducible complexity is a descendant of the teleological argument
for God (the argument from design or from complexity). This states that
complex functionality in the natural world which looks designed is
evidence of an intelligent creator. William Paley famously argued, in his 1802 watchmaker analogy,
that complexity in nature implies a God for the same reason that the
existence of a watch implies the existence of a watchmaker. This argument has a long history, and one can trace it back at least as far as Cicero's De Natura Deorum ii.34, written in 45 BC.
Up to the 18th century
Galen
(1st and 2nd centuries AD) wrote about the large number of parts of the
body and their relationships, which observation was cited as evidence
for creation.
The idea that the interdependence between parts would have implications
for the origins of living things was raised by writers starting with Pierre Gassendi in the mid-17th century and by John Wilkins
(1614-1672), who wrote (citing Galen), "Now to imagine, that all these
things, according to their several kinds, could be brought into this
regular frame and order, to which such an infinite number of Intentions
are required, without the contrivance of some wise Agent, must needs be
irrational in the highest degree." In the late 17th-century, Thomas Burnet referred to "a multitude of pieces aptly joyn'd" to argue against the eternity of life. In the early 18th century, Nicolas Malebranche
wrote "An organized body contains an infinity of parts that mutually
depend upon one another in relation to particular ends, all of which
must be actually formed in order to work as a whole", arguing in favor
of preformation, rather than epigenesis, of the individual; and a similar argument about the origins of the individual was made by other 18th-century students of natural history. In his 1790 book, The Critique of Judgment, Kant
is said by Guyer to argue that "we cannot conceive how a whole that
comes into being only gradually from its parts can nevertheless be the
cause of the properties of those parts".
19th century
Chapter XV of Paley's Natural Theology discusses at length what he called "relations" of parts of living things as an indication of their design.
Georges Cuvier applied his principle of the correlation of parts to describe an animal from fragmentary remains. For Cuvier, this related to another principle of his, the conditions of existence, which excluded the possibility of transmutation of species.
While he did not originate the term, Charles Darwin identified the argument as a possible way to falsify a prediction of the theory of evolution at the outset. In The Origin of Species
(1859), he wrote, "If it could be demonstrated that any complex organ
existed, which could not possibly have been formed by numerous,
successive, slight modifications, my theory would absolutely break down.
But I can find out no such case."
Darwin's theory of evolution challenges the teleological argument by
postulating an alternative explanation to that of an intelligent
designer—namely, evolution by natural selection. By showing how simple
unintelligent forces can ratchet up designs of extraordinary complexity
without invoking outside design, Darwin showed that an intelligent
designer was not the necessary conclusion to draw from complexity in
nature. The argument from irreducible complexity attempts to demonstrate
that certain biological features cannot be purely the product of
Darwinian evolution.
In the late 19th century, in a dispute between supporters of the adequacy of natural selection and those who held for inheritance of acquired characteristics, one of the arguments made repeatedly by Herbert Spencer, and followed by others, depended on what Spencer referred to as co-adaptation of co-operative parts, as in:
"We come now to Professor Weismann's
endeavour to disprove my second thesis — that it is impossible to
explain by natural selection alone the co-adaptation of co-operative
parts. It is thirty years since this was set forth in "The Principles of
Biology." In §166, I instanced the enormous horns of the extinct Irish elk,
and contended that in this and in kindred cases, where for the
efficient use of some one enlarged part many other parts have to be
simultaneously enlarged, it is out of the question to suppose that they
can have all spontaneously varied in the required proportions."
Darwin responded to Spencer's objections in chapter XXV of The Variation of Animals and Plants Under Domestication (1868).
The history of this concept in the dispute has been characterized: "An
older and more religious tradition of idealist thinkers were committed
to the explanation of complex adaptive contrivances by intelligent
design. ... Another line of thinkers, unified by the recurrent
publications of Herbert Spencer, also saw co-adaptation as a composed, irreducible whole, but sought to explain it by the inheritance of acquired characteristics."
St. George Jackson Mivart
raised the objection to natural selection that "Complex and
simultaneous co-ordinations ... until so far developed as to effect the
requisite junctions, are useless" which "amounts to the concept of "irreducible complexity" as defined by ... Michael Behe".
20th century
Hermann Muller,
in the early 20th century, discussed a concept similar to irreducible
complexity. However, far from seeing this as a problem for evolution, he
described the "interlocking" of biological features as a consequence to
be expected of evolution, which would lead to irreversibility of some
evolutionary changes.
He wrote, "Being thus finally woven, as it were, into the most intimate
fabric of the organism, the once novel character can no longer be
withdrawn with impunity, and may have become vitally necessary."
In 1974 the young Earth creationistHenry M. Morris introduced a similar concept in his book Scientific Creationism,
in which he wrote; "This issue can actually be attacked quantitatively,
using simple principles of mathematical probability. The problem is
simply whether a complex system, in which many components function
unitedly together, and in which each component is uniquely necessary to
the efficient functioning of the whole, could ever arise by random
processes."
In 1975 Thomas H. Frazzetta
published a book-length study of a concept similar to irreducible
complexity, explained by gradual, step-wise, non-teleological evolution.
Frazzetta wrote:
"A complex adaptation is one constructed of several
components that must blend together operationally to make the
adaptation "work". It is analogous to a machine whose performance
depends upon careful cooperation among its parts. In the case of the
machine, no single part can greatly be altered without changing the
performance of the entire machine."
The machine that he chose as an analog is the Peaucellier–Lipkin linkage,
and one biological system given extended description was the jaw
apparatus of a python. The conclusion of this investigation, rather than
that evolution of a complex adaptation was impossible, "awed by the
adaptations of living things, to be stunned by their complexity and
suitability", was "to accept the inescapable but not humiliating fact
that much of mankind can be seen in a tree or a lizard."
In 1981, Ariel Roth, in defense of the creation-science position in the trial McLean v. Arkansas,
said of "complex integrated structures": "This system would not be
functional until all the parts were there ... How did these parts
survive during evolution ...?"
In 1985 Cairns-Smith
wrote of "interlocking": "How can a complex collaboration between
components evolve in small steps?" and used the analogy of the
scaffolding called centering - used to build an arch
then removed afterwards: "Surely there was 'scaffolding'. Before the
multitudinous components of present biochemistry could come to lean
together they had to lean on something else." However, neither Muller or Cairns-Smith claimed their ideas as evidence of something supernatural.
An essay in support of creationism published in 1994 referred to bacterial flagella
as showing "multiple, integrated components", where "nothing about them
works unless every one of their complexly fashioned and integrated
components are in place". The author asked the reader to "imagine the
effects of natural selection on those organisms that fortuitously
evolved the flagella ... without the concommitant [sic] control mechanisms".
An early concept of irreducibly complex systems comes from Ludwig von Bertalanffy (1901-1972), an Austrian biologist. He believed that complex systems must be examined as complete, irreducible
systems in order to fully understand how they work. He extended his
work on biological complexity into a general theory of systems in a book
titled General Systems Theory.
After James Watson and Francis Crick published the structure of DNA in the early 1950s, General Systems Theory lost many of its adherents in the physical and biological sciences.
However, systems theory remained popular in the social sciences long after its demise in the physical and biological sciences.
Michael Behe developed his ideas on the concept around 1992, in the early days of the 'wedge movement',
and first presented his ideas about "irreducible complexity" in June
1993 when the "Johnson-Behe cadre of scholars" met at Pajaro Dunes in
California. He set out his ideas in the second edition of Of Pandas and People published in 1993, extensively revising Chapter 6 Biochemical Similarities with new sections on the complex mechanism of blood clotting and on the origin of proteins.
He first used the term "irreducible complexity" in his 1996 book Darwin's Black Box, to refer to certain complex biochemical cellular
systems. He posits that evolutionary mechanisms cannot explain the
development of such "irreducibly complex" systems. Notably, Behe credits
philosopher William Paley
for the original concept (alone among the predecessors) and suggests
that his application of the concept to biological systems is entirely
original.
Intelligent design advocates argue that irreducibly complex systems must have been deliberately engineered by some form of intelligence.
In 2001, Michael Behe
wrote: "[T]here is an asymmetry between my current definition of
irreducible complexity and the task facing natural selection. I hope to
repair this defect in future work." Behe specifically explained that the
"current definition puts the focus on removing a part from an already
functioning system", but the "difficult task facing Darwinian evolution,
however, would not be to remove parts from sophisticated pre-existing
systems; it would be to bring together components to make a new system
in the first place". In the 2005 Kitzmiller v. Dover Area School District trial, Behe testified under oath that he "did not judge [the asymmetry] serious enough to [have revised the book] yet."
Behe additionally testified that the presence of irreducible
complexity in organisms would not rule out the involvement of
evolutionary mechanisms in the development of organic life. He further
testified that he knew of no earlier "peer reviewed articles in
scientific journals discussing the intelligent design of the blood
clotting cascade," but that there were "probably a large number of peer
reviewed articles in science journals that demonstrate that the blood
clotting system is indeed a purposeful arrangement of parts of great
complexity and sophistication." (The judge ruled that "intelligent design is not science and is essentially religious in nature".)
According to the theory of evolution, genetic variations occur
without specific design or intent. The environment "selects" the
variants that have the highest fitness, which are then passed on to the
next generation of organisms. Change occurs by the gradual operation of
natural forces over time, perhaps slowly, perhaps more quickly (see punctuated equilibrium). This process is able to adapt complex structures from simpler beginnings, or convert complex structures from one function to another (see spandrel). Most intelligent design advocates accept that evolution occurs through mutation and natural selection at the "micro level",
such as changing the relative frequency of various beak lengths in
finches, but assert that it cannot account for irreducible complexity,
because none of the parts of an irreducible system would be functional
or advantageous until the entire system is in place.
The mousetrap example
Michael Behe believes that many aspects of life show evidence of design, using the mousetrap in an analogy disputed by others.
Behe uses the mousetrap as an illustrative example of this concept. A
mousetrap consists of five interacting pieces: the base, the catch, the
spring, the hammer, and the hold-down bar. All of these must be in
place for the mousetrap to work, as the removal of any one piece
destroys the function of the mousetrap. Likewise, he asserts that
biological systems require multiple parts working together in order to
function. Intelligent design advocates claim that natural selection
could not create from scratch those systems for which science is
currently unable to find a viable evolutionary pathway of successive,
slight modifications, because the selectable function is only present
when all parts are assembled.
In his 2008 book Only A Theory, biologist Kenneth R. Miller challenges Behe's claim that the mousetrap is irreducibly complex.
Miller observes that various subsets of the five components can be
devised to form cooperative units, ones that have different functions
from the mousetrap and so, in biological terms, could form functional spandrels
before being adapted to the new function of catching mice. In an
example taken from his high school experience, Miller recalls that one
of his classmates
...struck upon the brilliant idea of
using an old, broken mousetrap as a spitball catapult, and it worked
brilliantly.... It had worked perfectly as something other than a
mousetrap.... my rowdy friend had pulled a couple of parts --probably
the hold-down bar and catch-- off the trap to make it easier to conceal
and more effective as a catapult... [leaving] the base, the spring, and
the hammer. Not much of a mousetrap, but a helluva spitball launcher....
I realized why [Behe's] mousetrap analogy had bothered me. It was
wrong. The mousetrap is not irreducibly complex after all.
Other systems identified by Miller that include mousetrap components include the following:
use the spitball launcher as a tie clip (same three-part system with different function)
remove the spring from the spitball launcher/tie clip to create a two-part key chain (base + hammer)
glue the spitball launcher/tie clip to a sheet of wood to create a clipboard (launcher + glue + wood)
remove the hold-down bar for use as a toothpick (single element system)
The point of the reduction is that—in biology—most or all of the
components were already at hand, by the time it became necessary to
build a mousetrap. As such, it required far fewer steps to develop a
mousetrap than to design all the components from scratch.
Thus, the development of the mousetrap, said to consist of five
different parts which had no function on their own, has been reduced to
one step: the assembly from parts that are already present, performing
other functions.
Consequences
Supporters
of intelligent design argue that anything less than the complete form
of such a system or organ would not work at all, or would in fact be a detriment
to the organism, and would therefore never survive the process of
natural selection. Although they accept that some complex systems and
organs can be explained by evolution, they claim that organs and biological features which are irreducibly complex
cannot be explained by current models, and that an intelligent designer
must have created life or guided its evolution. Accordingly, the debate
on irreducible complexity concerns two questions: whether irreducible
complexity can be found in nature, and what significance it would have
if it did exist in nature.
Behe argues that organs and biological features which are irreducibly complex cannot be wholly explained by current models of evolution. In explicating his definition of "irreducible complexity" he notes that:
An irreducibly complex system cannot be produced directly
(that is, by continuously improving the initial function, which
continues to work by the same mechanism) by slight, successive
modifications of a precursor system, because any precursor to an
irreducibly complex system that is missing a part is by definition
nonfunctional.
Irreducible complexity is not an argument that evolution does not
occur, but rather an argument that it is "incomplete". In the last
chapter of Darwin's Black Box, Behe goes on to explain his view that irreducible complexity is evidence for intelligent design.
Mainstream critics, however, argue that irreducible complexity, as
defined by Behe, can be generated by known evolutionary mechanisms.
Behe's claim that no scientific literature adequately modeled the
origins of biochemical systems through evolutionary mechanisms has been
challenged by TalkOrigins. The judge in the Dover trial wrote "By defining irreducible complexity in the way that he has, Professor Behe attempts to exclude the phenomenon of exaptation by definitional fiat, ignoring as he does so abundant evidence which refutes his argument. Notably, the NAS has rejected Professor Behe's claim for irreducible complexity..."
Stated examples
Behe and others have suggested a number of biological features that they believed to be irreducibly complex.
Blood clotting cascade
The process of blood clotting or coagulation cascade in vertebrates is a complex biological pathway which is given as an example of apparent irreducible complexity.
The irreducible complexity argument assumes that the necessary
parts of a system have always been necessary, and therefore could not
have been added sequentially. However, in evolution, something which is
at first merely advantageous can later become necessary. Natural selection
can lead to complex biochemical systems being built up from simpler
systems, or to existing functional systems being recombined as a new
system with a different function. For example, one of the clotting factors that Behe listed as a part of the clotting cascade (Factor XII,
also called Hageman factor) was later found to be absent in whales,
demonstrating that it is not essential for a clotting system.
Many purportedly irreducible structures can be found in other organisms
as much simpler systems that utilize fewer parts. These systems, in
turn, may have had even simpler precursors that are now extinct. Behe
has responded to critics of his clotting cascade arguments by suggesting
that homology is evidence for evolution, but not for natural selection.
The "improbability argument" also misrepresents natural
selection. It is correct to say that a set of simultaneous mutations
that form a complex protein structure is so unlikely as to be
unfeasible, but that is not what Darwin advocated. His explanation is
based on small accumulated changes that take place without a final goal.
Each step must be advantageous in its own right, although biologists
may not yet understand the reason behind all of them—for example, jawless fish accomplish blood clotting with just six proteins instead of the full ten.
Eye
Stages in the evolution of the eye (a) A pigment spot (b) A simple pigment cup (c) The simple optic cup found in abalone (d) The complex lensed eye of the marine snail and the octopus
The eye
is frequently cited by intelligent design and creationism advocates as a
purported example of irreducible complexity. Behe used the "development
of the eye problem" as evidence for intelligent design in Darwin's Black Box.
Although Behe acknowledged that the evolution of the larger anatomical
features of the eye have been well-explained, he pointed out that the
complexity of the minute biochemical reactions required at a molecular
level for light sensitivity still defies explanation. Creationist Jonathan Sarfati
has described the eye as evolutionary biologists' "greatest challenge
as an example of superb 'irreducible complexity' in God's creation",
specifically pointing to the supposed "vast complexity" required for
transparency.
In an often misquoted passage from On the Origin of Species, Charles Darwin
appears to acknowledge the eye's development as a difficulty for his
theory. However, the quote in context shows that Darwin actually had a
very good understanding of the evolution of the eye (see fallacy of quoting out of context).
He notes that "to suppose that the eye ... could have been formed by
natural selection, seems, I freely confess, absurd in the highest
possible degree". Yet this observation was merely a rhetorical device
for Darwin. He goes on to explain that if gradual evolution of the eye
could be shown to be possible, "the difficulty of believing that a
perfect and complex eye could be formed by natural selection ... can
hardly be considered real". He then proceeded to roughly map out a
likely course for evolution using examples of gradually more complex
eyes of various species.
The eyes of vertebrates (left) and invertebrates such as the octopus (right) developed independently: vertebrates evolved an inverted retina with a blind spot over their optic disc, whereas octopuses avoided this with a non-inverted retina. (1 photo-receptors, 2 neural tissue, 3 optic nerve)
Since Darwin's day, the eye's ancestry has become much better
understood. Although learning about the construction of ancient eyes
through fossil evidence is problematic due to the soft tissues leaving
no imprint or remains, genetic and comparative anatomical evidence has
increasingly supported the idea of a common ancestry for all eyes.
Current evidence does suggest possible evolutionary lineages for
the origins of the anatomical features of the eye. One likely chain of
development is that the eyes originated as simple patches of photoreceptor cells
that could detect the presence or absence of light, but not its
direction. When, via random mutation across the population, the
photosensitive cells happened to have developed on a small depression,
it endowed the organism with a better sense of the light's source. This
small change gave the organism an advantage over those without the
mutation. This genetic trait would then be "selected for" as those with
the trait would have an increased chance of survival, and therefore
progeny, over those without the trait. Individuals with deeper
depressions would be able to discern changes in light over a wider field
than those individuals with shallower depressions. As ever deeper
depressions were advantageous to the organism, gradually, this
depression would become a pit into which light would strike certain
cells depending on its angle. The organism slowly gained increasingly
precise visual information. And again, this gradual process continued as
individuals having a slightly shrunken aperture of the eye had an advantage over those without the mutation as an aperture increases how collimated the light is at any one specific group of photoreceptors. As this trait developed, the eye became effectively a pinhole camera which allowed the organism to dimly make out shapes—the nautilus
is a modern example of an animal with such an eye. Finally, via this
same selection process, a protective layer of transparent cells over the
aperture was differentiated into a crude lens, and the interior of the eye was filled with humours to assist in focusing images.[68][69][70]
In this way, eyes are recognized by modern biologists as actually a
relatively unambiguous and simple structure to evolve, and many of the
major developments of the eye's evolution are believed to have taken
place over only a few million years, during the Cambrian explosion.
Behe asserts that this is only an explanation of the gross anatomical
steps, however, and not an explanation of the changes in discrete
biochemical systems that would have needed to take place.
Behe maintains that the complexity of light sensitivity at the
molecular level and the minute biochemical reactions required for those
first "simple patches of photoreceptor[s]" still defies explanation, and
that the proposed series of infinitesimal steps to get from patches of
photoreceptors to a fully functional eye would actually be considered
great, complex leaps in evolution if viewed on the molecular scale.
Other intelligent design proponents claim that the evolution of the
entire visual system would be difficult rather than the eye alone.
Flagella
The flagella of certain bacteria constitute a molecular motor
requiring the interaction of about 40 different protein parts. Behe
presents this as a prime example of an irreducibly complex structure
defined as "a single system composed of several well-matched,
interacting parts that contribute to the basic function, wherein the
removal of any one of the parts causes the system to effectively cease
functioning", and argues that since "an irreducibly complex system that
is missing a part is by definition nonfunctional", it could not have
evolved gradually through natural selection.
Reducible complexity. In contrast to Behe's claims, many
proteins can be deleted or mutated and the flagellum still works, even
though sometimes at reduced efficiency.
In fact, the composition of flagella is surprisingly diverse across
bacteria with many proteins only found in some species but not others.
Hence the flagellar apparatus is clearly very flexible in evolutionary
terms and perfectly able to lose or gain protein components. Further
studies have shown that, contrary to claims of "irreducible complexity",
flagella and the type-III secretion system
share several components which provides strong evidence of a shared
evolutionary history (see below). In fact, this example shows how a
complex system can evolve from simpler components. Multiple processes were involved in the evolution of the flagellum, including horizontal gene transfer.
Evolution from type three secretion systems. The basal body of the flagella has been found to be similar to the Type III secretion system (TTSS), a needle-like structure that pathogenic germs such as Salmonella and Yersinia pestis use to inject toxins into living eucaryote cells.
The needle's base has ten elements in common with the flagellum, but it
is missing forty of the proteins that make a flagellum work.
The TTSS system negates Behe's claim that taking away any one of the
flagellum's parts would prevent the system from functioning. On this
basis, Kenneth Miller notes that, "The parts of this supposedly irreducibly complex system actually have functions of their own."
Studies have also shown that similar parts of the flagellum in
different bacterial species can have different functions despite showing
evidence of common descent, and that certain parts of the flagellum can
be removed without completely eliminating its functionality.
Dembski has argued that phylogenetically, the TTSS is found in a
narrow range of bacteria which makes it seem to him to be a late
innovation, whereas flagella are widespread throughout many bacterial
groups, and he argues that it was an early innovation.
Against Dembski's argument, different flagella use completely different
mechanisms, and publications show a plausible path in which bacterial
flagella could have evolved from a secretion system.
Cilium motion
The cilium construction of axoneme microtubules movement by the sliding of dynein protein was cited by Behe as an example of irreducible complexity. He further said that the advances in knowledge in the subsequent 10 years had shown that the complexity of intraflagellar transport for two hundred components cilium and many other cellular structures is substantially greater than was known earlier.
Bombardier beetle's defense mechanism
The bombardier beetle is able to defend itself by directing a spray of hot fluid at an attacker. The mechanism involves a system for mixing hydroquinones and hydrogen peroxide,
which react violently to attain a temperature near boiling point, and
in some species a nozzle which allows the spray to be directed
accurately in any direction.
The unique combination of features of the bombardier beetle's
defense mechanism—strongly exothermic reactions, boiling-hot fluids, and
explosive release—have been claimed by creationists and proponents of intelligent design to be examples of irreducible complexity.
Biologists such as the taxonomist Mark Isaak note however that
step-by-step evolution of the mechanism could readily have occurred. In
particular, quinones are precursors to sclerotin, used to harden the skeleton of many insects, while peroxide is a common by-product of metabolism.
Response of the scientific community
Like
intelligent design, the concept it seeks to support, irreducible
complexity has failed to gain any notable acceptance within the scientific community.
Reducibility of "irreducible" systems
Researchers
have proposed potentially viable evolutionary pathways for allegedly
irreducibly complex systems such as blood clotting, the immune system and the flagellum - the three examples Behe proposed. John H. McDonald even showed his example of a mousetrap to be reducible. If irreducible complexity is an insurmountable obstacle to evolution, it should not be possible to conceive of such pathways.
Niall Shanks and Karl H. Joplin, both of East Tennessee State University,
have shown that systems satisfying Behe's characterization of
irreducible biochemical complexity can arise naturally and spontaneously
as the result of self-organizing chemical processes.
They also assert that what evolved biochemical and molecular systems
actually exhibit is "redundant complexity"—a kind of complexity that is
the product of an evolved biochemical process. They claim that Behe
overestimated the significance of irreducible complexity because of his
simple, linear view of biochemical reactions, resulting in his taking
snapshots of selective features of biological systems, structures, and
processes, while ignoring the redundant complexity of the context in
which those features are naturally embedded. They also criticized his
over-reliance of overly simplistic metaphors, such as his mousetrap.
A computer model of the co-evolution of proteins binding to DNA in the peer-reviewed journal Nucleic Acids Research
consisted of several parts (DNA binders and DNA binding sites) which
contribute to the basic function; removal of either one leads
immediately to the death of the organism. This model fits the definition
of irreducible complexity exactly, yet it evolves. (The program can be run from Ev program.)
In addition, research published in the peer-reviewed journal Nature has shown that computer simulations of evolution demonstrate that it is possible for complex features to evolve naturally.
One can compare a mousetrap with a cat in this context. Both
normally function so as to control the mouse population. The cat has
many parts that can be removed leaving it still functional; for example,
its tail can be bobbed, or it can lose an ear in a fight. Comparing the
cat and the mousetrap, then, one sees that the mousetrap (which is not
alive) offers better evidence, in terms of irreducible complexity, for
intelligent design than the cat. Even looking at the mousetrap analogy,
several critics have described ways in which the parts of the mousetrap
could have independent uses or could develop in stages, demonstrating
that it is not irreducibly complex.
Moreover, even cases where removing a certain component in an
organic system will cause the system to fail do not demonstrate that the
system could not have been formed in a step-by-step, evolutionary
process. By analogy, stone arches are irreducibly complex—if you remove
any stone the arch will collapse—yet humans build them easily enough, one stone at a time, by building over centering that is removed afterward. Similarly, naturally occurring arches of stone form by the weathering away of bits of stone from a large concretion that has formed previously.
Evolution can act to simplify as well as to complicate. This
raises the possibility that seemingly irreducibly complex biological
features may have been achieved with a period of increasing complexity,
followed by a period of simplification.
A team led by Joseph Thornton, assistant professor of biology at the University of Oregon's
Center for Ecology and Evolutionary Biology, using techniques for
resurrecting ancient genes, reconstructed the evolution of an apparently
irreducibly complex molecular system. The April 7, 2006 issue of Science published this research.
Irreducible complexity may not actually exist in nature, and the
examples given by Behe and others may not in fact represent irreducible
complexity, but can be explained in terms of simpler precursors. The
theory of facilitated variation challenges irreducible complexity. Marc W. Kirschner, a professor and chair of Department of Systems Biology at Harvard Medical School, and John C. Gerhart, a professor in Molecular and Cell Biology, University of California, Berkeley,
presented this theory in 2005. They describe how certain mutation and
changes can cause apparent irreducible complexity. Thus, seemingly
irreducibly complex structures are merely "very complex", or they are
simply misunderstood or misrepresented.
Gradual adaptation to new functions
The precursors of complex systems, when they are not useful in
themselves, may be useful to perform other, unrelated functions.
Evolutionary biologists argue that evolution often works in this kind of
blind, haphazard manner in which the function of an early form is not
necessarily the same as the function of the later form. The term used
for this process is exaptation. The mammalian middle ear (derived from a jawbone) and the panda's thumb (derived from a wrist bone spur) provide classic examples. A 2006 article in Nature demonstrates intermediate states leading toward the development of the ear in a Devonian fish (about 360 million years ago).
Furthermore, recent research shows that viruses play a heretofore
unexpected role in evolution by mixing and matching genes from various
hosts.
Arguments for irreducibility often assume that things started out
the same way they ended up—as we see them now. However, that may not
necessarily be the case. In the Dover trial an expert witness for
the plaintiffs, Ken Miller, demonstrated this possibility using Behe's
mousetrap analogy. By removing several parts, Miller made the object
unusable as a mousetrap, but he pointed out that it was now a perfectly
functional, if unstylish, tie clip.
Methods by which irreducible complexity may evolve
Irreducible complexity can be seen as equivalent to an "uncrossable valley" in a fitness landscape.
A number of mathematical models of evolution have explored the
circumstances under which such valleys can, nevertheless, be crossed.
Behe argues that the theory that irreducibly complex systems
could not have evolved can be falsified by an experiment where such
systems are evolved. For example, he posits taking bacteria with no flagellum
and imposing a selective pressure for mobility. If, after a few
thousand generations, the bacteria evolved the bacterial flagellum, then
Behe believes that this would refute his theory.
Other critics take a different approach, pointing to experimental
evidence that they consider falsification of the argument for
intelligent design from irreducible complexity. For example, Kenneth Miller describes the lab work of Barry G. Hall on E. coli as showing that "Behe is wrong".
Other evidence that irreducible complexity is not a problem for evolution comes from the field of computer science,
which routinely uses computer analogues of the processes of evolution
in order to automatically design complex solutions to problems. The
results of such genetic algorithms
are frequently irreducibly complex since the process, like evolution,
both removes non-essential components over time as well as adding new
components. The removal of unused components with no essential function,
like the natural process where rock underneath a natural arch
is removed, can produce irreducibly complex structures without
requiring the intervention of a designer. Researchers applying these
algorithms automatically produce human-competitive designs—but no human
designer is required.
Argument from ignorance
Intelligent
design proponents attribute to an intelligent designer those biological
structures they believe are irreducibly complex and therefore they say a
natural explanation is insufficient to account for them.
However, critics view irreducible complexity as a special case of the
"complexity indicates design" claim, and thus see it as an argument from ignorance and as a God-of-the-gaps argument.
Eugenie Scott and Glenn Branch of the National Center for Science Education
note that intelligent design arguments from irreducible complexity rest
on the false assumption that a lack of knowledge of a natural
explanation allows intelligent design proponents to assume an
intelligent cause, when the proper response of scientists would be to
say that we don't know, and further investigation is needed.
Other critics describe Behe as saying that evolutionary explanations
are not detailed enough to meet his standards, while at the same time
presenting intelligent design as exempt from having to provide any
positive evidence at all.
False dilemma
Irreducible
complexity is at its core an argument against evolution. If truly
irreducible systems are found, the argument goes, then intelligent design must be the correct explanation for their existence. However, this conclusion is based on the assumption that current evolutionary theory and intelligent design are the only two valid models to explain life, a false dilemma.
The argument from reason is an argument against metaphysical naturalism and for the existence of God (or at least a supernatural being that is the source of human reason). The best-known defender of the argument is C. S. Lewis. Lewis first defended the argument at length in his 1947 book, Miracles: A Preliminary Study. In the second edition of Miracles (1960), Lewis substantially revised and expanded the argument.
Metaphysical naturalism
is the view that nature as studied by the natural sciences is all that
exists. Naturalists deny the existence of a supernatural God, souls, an
afterlife, or anything supernatural. Nothing exists outside or beyond
the physical universe.
The argument from reason seeks to show that naturalism is self-refuting, or otherwise false and indefensible.
According to Lewis,
One absolutely central
inconsistency ruins [the naturalistic worldview].... The whole picture
professes to depend on inferences from observed facts. Unless inference
is valid, the whole picture disappears.... [U]nless Reason is an
absolute--all is in ruins. Yet those who ask me to believe this world
picture also ask me to believe that Reason is simply the unforeseen and
unintended by-product of mindless matter at one stage of its endless and
aimless becoming. Here is flat contradiction. They ask me at the same
moment to accept a conclusion and to discredit the only testimony on
which that conclusion can be based.
More precisely, Lewis's argument from reason can be stated as follows:
1. No belief is rationally inferred if it can be fully explained in terms of nonrational causes.
Support: Reasoning requires insight into logical relations. A process
of reasoning (P therefore Q) is rational only if the reasoner sees that
Q follows from, or is supported by, P, and accepts Q on that basis.
Thus, reasoning is trustworthy (or "valid", as Lewis sometimes says)
only if it involves a special kind of causality, namely, rational
insight into logical implication or evidential support. If a bit of
reasoning can be fully explained by nonrational causes, such as fibers
firing in the brain or a bump on the head, then the reasoning is not
reliable, and cannot yield knowledge. Consider this example: Person A
refuses to go near the neighbor’s dog because he had a bad childhood
experience with dogs. Person B refuses to go near the neighbor’s dog
because one month ago he saw it attack someone. Both have given a reason
for staying away from the dog, but person A’s reason is the result of
nonrational causes,
while person B has given an explanation for his behavior following from
rational inference (animals exhibit patterns of behavior; these
patterns are likely to be repeated; this dog has exhibited aggression
towards someone who approached it; there is a good chance that the dog
may exhibit the same behavior towards me if I approach it). Consider a
second example: person A says that he is afraid to climb to the 8th
story of a bank building because he and humans in general have a natural
fear of heights resulting from the processes of evolution and natural
selection. He has given an explanation of his fear, but since his fear
results from nonrational causes (natural selection), his argument does
not follow from logical inference.
2. If naturalism is true, then all beliefs can be fully explained in terms of nonrational causes.
Support: Naturalism holds that nature is all that exists, and that
all events in nature can in principle be explained without invoking
supernatural or other nonnatural causes. Standardly, naturalists claim
that all events must have physical causes, and that human thoughts can
ultimately be explained in terms of material causes or physical events
(such as neurochemical events in the brain) that are nonrational.
3. Therefore, if naturalism is true, then no belief is rationally inferred (from 1 and 2).
4. We have good reason to accept naturalism only if it can be rationally inferred from good evidence.
5. Therefore, there is not, and cannot be, good reason to accept naturalism.
In short, naturalism undercuts itself. If naturalism is true, then we cannot sensibly believe it or virtually anything else.
In some versions of the argument from reason, Lewis extends the
argument to defend a further conclusion: that human reason depends on an
eternal, self-existent rational Being (God). This extension of the
argument from reason states:
1. Since everything in nature can be wholly explained in
terms of nonrational causes, human reason (more precisely, the power of
drawing conclusions based solely on the rational cause of logical
insight) must have a source outside of nature.
2. If human reason came from non-reason it would lose all rational credentials and would cease to be reason.
3. So, human reason cannot come from non-reason (from 2).
4. So human reason must come from a source outside nature that is itself rational (from 1 and 3).
5. This supernatural source of reason may itself be
dependent on some further source of reason, but a chain of such
dependent sources cannot go on forever. Eventually, we must reason back
to the existence of eternal, non-dependent source of human reason.
6. Therefore, there exists an eternal, self-existent,
rational Being who is the ultimate source of human reason. This Being we
call God (from 4-5). (Lewis, Miracles, chap. 4)
Anscombe's criticism
On 2 February 1948, Oxford philosopher Elizabeth Anscombe read a paper to the Oxford Socratic Club criticizing the version of the argument from reason contained in the third chapter of Lewis's Miracles.
Her first criticism was against the use of the word "irrational"
by Lewis (Anscombe 1981: 225-26). Her point was that there is an
important difference between irrational causes of belief, such as
wishful thinking, and nonrational causes, such as neurons firing in the
brain, that do not obviously lead to faulty reasoning. Lewis accepted
the criticism and amended the argument, basing it on the concept of
nonrational causes of belief (as in the version provided in this
article).
Anscombe's second criticism questioned the intelligibility of
Lewis's intended contrast between "valid" and "invalid" reasoning. She
wrote: "What can you mean by 'valid' beyond what would be
indicated by the explanation you would give for distinguishing between
valid and invalid, and what in the naturalistic hypothesis prevents that
explanation from being given and from meaning what it does?" (Anscombe
1981: 226) Her point is that it makes no sense to contrast "valid" and
"invalid" reasoning unless it is possible for some forms of reasoning to
be valid. Lewis later conceded (Anscombe 1981: 231) that "valid" was a
bad word for what he had in mind. Lewis didn't mean to suggest that if
naturalism is true, no arguments can be given in which the conclusions
follow logically from the premises. What he meant is that a process of
reasoning is "veridical", that is, reliable as a method of pursuing
knowledge and truth, only if it cannot be entirely explained by
nonrational causes.
Anscombe's third objection was that Lewis failed to distinguish
between different senses of the terms "why", "because", and
"explanation", and that what counts as a "full" explanation varies by
context (Anscombe 1981: 227-31). In the context of ordinary life,
"because he wants a cup of tea" may count as a perfectly satisfactory
explanation of why Peter is boiling water. Yet such a purposive
explanation would not count as a full explanation (or an explanation at
all) in the context of physics or biochemistry. Lewis accepted this
criticism, and created a revised version of the argument in which the
distinction between "because" in the sense of physical causality, and
"because" in the sense of evidential support, became the central point
of the argument (this is the version described in this article).
More recent critics have argued that Lewis's argument at best
refutes only strict forms of naturalism that seek to explain everything
in terms ultimately reducible to physics or purely mechanistic causes.
So-called "broad" naturalists that see consciousness as an "emergent"
non-physical property of complex brains would agree with Lewis that
different levels or types of causation exist in nature, and that
rational inferences are not fully explainable by nonrational causes.
Other critics have objected that Lewis's argument from reason
fails because the causal origins of beliefs are often irrelevant to
whether those beliefs are rational, justified, warranted, etc. Anscombe,
for example, argues that "if a man has reasons, and they are good
reasons, and they are genuinely his reasons, for thinking something—then
his thought is rational, whatever causal statements we make about him"
(Anscombe 1981: 229). On many widely accepted theories of knowledge and
justification, questions of how beliefs were ultimately caused (e.g., at
the level of brain neurochemistry) are viewed as irrelevant to whether
those beliefs are rational or justified. Some defenders of Lewis claim that this objection misses the mark, because his argument is
directed at what he calls the "veridicalness" of acts of reasoning
(i.e., whether reasoning connects us with objective reality or truth),
rather than with whether any inferred beliefs can be rational or
justified in a materialistic world.
Criticism by eliminative materialists
The
argument from reason claims that if beliefs, desires, and other
contentful mental states cannot be accounted for in naturalism then
naturalism is false. Eliminative materialism
maintains that propositional attitudes such as beliefs and desires,
among other intentional mental states that have content, cannot be
explained on naturalism and therefore concludes that such entities do
not exist. Even if successful, the argument from reason only rules out
certain forms of naturalism and fails to argue against a conception of
naturalism which accepts eliminative materialism to be the correct scientific account of human cognition.
Criticism by computationalists
Some
people think it is easy to refute any argument from reason just by
appealing to the existence of computers. Computers, according to the
objection, reason, they are also undeniably a physical system, but they
are also rational. So whatever incompatibility there might be between
mechanism and reason must be illusory. Since computers do not operate on beliefs and desires and yet come to justified conclusions about the world as in object recognition or proving mathematical theorems,
it should not be a surprise on naturalism that human brains can do the
same. According to John Searle, computation and syntax are
observer-relative but the cognition of the human mind is not
observer-relative. Such a position seems to be bolstered by arguments from the indeterminacy of translation offered by Quine and Kripke's skeptical paradox regarding meaning which support the conclusion that the interpretation of algorithms is observer-relative. However, according to the Church–Turing thesis the human brain is a computer and computationalism is a viable and developing research program in neuroscience
for understanding how the brain works. Moreover, any indeterminacy of
brain cognition does not entail human cognitive faculties are unreliable
because natural selection has ensured they result in the survival of biological organisms, contrary to claims by the evolutionary argument against naturalism.
Similar views by other thinkers
Philosophers such as Victor Reppert, William Hasker and Alvin Plantinga have expanded on the argument from reason, and credit C.S. Lewis as an important influence on their thinking.
Lewis never claimed that he invented the argument from reason; in fact, he refers to it as a "venerable philosophical chestnut." Early versions of the argument occur in the works of Arthur Balfour (see, e.g., The Foundations of Belief, 1879, chap. 13) and G.K. Chesterton. In Chesterton's 1908 book Orthodoxy,
in a chapter titled "The Suicide of Thought", he writes of the "great
and possible peril . . . that the human intellect is free to destroy
itself....It is idle to talk always of the alternative of reason and
faith. It is an act of faith to assert that our thoughts have any
relation to reality at all. If you are merely a sceptic, you must sooner
or later ask yourself the question, "Why should anything go right; even
observation and deduction? Why should not good logic be as misleading
as bad logic? They are both movements in the brain of a bewildered ape?"
Similarly, Chesterton asserts that the argument is a fundamental, if unstated, tenet of Thomism in his 1933 book St. Thomas Aquinas: "The Dumb Ox":
Thus, even those who appreciate the metaphysical depth of
Thomism in other matters have expressed surprise that he does not deal
at all with what many now think the main metaphysical question; whether
we can prove that the primary act of recognition of any reality is real.
The answer is that St. Thomas recognised instantly, what so many modern
sceptics have begun to suspect rather laboriously; that a man must
either answer that question in the affirmative, or else never answer any
question, never ask any question, never even exist intellectually, to
answer or to ask. I suppose it is true in a sense that a man can be a
fundamental sceptic, but he cannot be anything else: certainly not even a
defender of fundamental scepticism. If a man feels that all the
movements of his own mind are meaningless, then his mind is meaningless,
and he is meaningless; and it does not mean anything to attempt to
discover his meaning. Most fundamental sceptics appear to survive,
because they are not consistently sceptical and not at all fundamental.
They will first deny everything and then admit something, if for the
sake of argument--or often rather of attack without argument. I saw an
almost startling example of this essential frivolity in a professor of
final scepticism, in a paper the other day. A man wrote to say that he
accepted nothing but Solipsism, and added that he had often wondered it
was not a more common philosophy. Now Solipsism simply means that a man
believes in his own existence, but not in anybody or anything else. And
it never struck this simple sophist, that if his philosophy was true,
there obviously were no other philosophers to profess it.
In Miracles, Lewis himself quotes J. B. S. Haldane, who appeals to a similar line of reasoning in his 1927 book, Possible Worlds:
"If my mental processes are determined wholly by the motions of atoms
in my brain, I have no reason to suppose that my beliefs are true ...
and hence I have no reason for supposing my brain to be composed of
atoms."
Other versions of the argument from reason occur in C.E.M. Joad's Guide to Modern Philosophy (London: Faber, 1933, pp. 58–59), Richard Taylor's Metaphysics (Englewood Cliffs, NJ: Prentice Hall, 3rd ed., 1983, pp. 104–05), and J. P. Moreland's Scaling the Secular City: A Defense of Christianity (Grand Rapids, MI: Baker, 1987, chap. 3).
Peter Kreeft used the argument from reason to create a formulation of the argument from consciousness for the existence of God. He phrased it as follows:
"We experience the universe as intelligible. This intelligibility means that the universe is graspable by intelligence."
"Either this intelligible universe and the finite minds so well
suited to grasp it are the products of intelligence, or both
intelligibility and intelligence are the products of blind chance."
"Not blind chance."
"Therefore this intelligible universe and the finite minds so well suited to grasp it are the products of intelligence."
He used the argument from reason to affirm the third premise.
