RICHARD DAWKINS
THE BLIND
WATCHMAKER
RICHARD DAWKINS
THE BLIND
WATCHMAKER
PENGUIN BOOKS
A B O U T THE AUTHOR
Richard Dawkins was born in Nairobi in 1941. He was educated at
Oxford University, and after graduation remained there to work
for his doctorate with the Nobel Prize-winning ethologist Niko
Tinbergen. From 1967 to 1969 he was an Assistant Professor of
Zoology at the University of California at Berkeley. In 1970 he became
a Lecturer in Zoology at Oxford University and a Fellow of New
College. In 1995 he became the first Charles Simonyi Professor of the
Public Understanding of Science at Oxford University.
Richard Dawkins's first book. The Selfish Gene (1976; second edition,
1989), became an immediate international bestseller and, like The
Blind Watchmaker, was translated into all the major languages. Its
sequel, The Extended Phenotype, followed in 1982. His other bestsellers include River Out of Eden (1995) and Climbing Mount
Improbable (1996; Penguin, 1997).
Richard Dawkins won both the Royal Society of Literature Award and
the Los Angeles Times Literary Prize in 1987 for The Blind
Watchmaker. The television film of the book, shown in the Horizon
series, won the Sci-Tech Prize for the Best Science Programme of 1987.
He has also won the 1989 Silver Medal of the Zoological Society of
London and the 1990 Royal Society Michael Faraday Award for the
furtherance of the public understanding of science. In 1994 he won
the Nakayama Prize for Human Science and has been awarded an
Honorary D.Litt. by the University of St Andrews and by the
Australian National University, Canberra.
CONTENTS
Preface
Chapter I Explaining the very improbable
Chapter 2 Good design
Chapter 3 Accumulating small change
Chapter 4 Making tracks through animal space
Chapter 5 The power and the archives
Chapter 6 Origins and miracles
Chapter 7
Constructive evolution
Chapter 8 Explosions and spirals
Chapter 9
Puncturing punctuationism
Chapter 10 The one true tree of life
Chapter 11 Doomed rivals
Bibliography
Appendix (1991): Computer programs and 'The
Evolution of Evolvability'
Index
PREFACE
This book is written in the conviction that our own existence once
presented the greatest of all mysteries, but that it is a mystery no
longer because it is solved. Darwin and Wallace solved it, though we
shall continue to add footnotes to their solution for a while yet. I wrote
the book because I was surprised that so many people seemed not only
unaware of the elegant and beautiful solution to this deepest of
problems but, incredibly, in many cases actually unaware that there
was a problem in the first place!
The problem is that of complex design. The computer on which I am
writing these words has an information storage capacity of about 64
kilobytes (one byte is used to hold each character of text). The
computer was consciously designed and deliberately manufactured.
The brain with which you are understanding my words is an array of
some ten million kiloneurones. Many of these billions of nerve cells
have each more than a thousand 'electric wires' connecting them to
other neurones. Moreover, at the molecular genetic level, every single
one of more than a trillion cells in the body contains about a thousand
times as much precisely-coded digital information as my entire
computer. The complexity of living organisms is matched by the
elegant efficiency of their apparent design. If anyone doesn't agree that
this amount of complex design cries out for an explanation, I give up.
No, on second thoughts I don't give up, because one of my aims in the
book is to convey something of the sheer wonder of biological
complexity to those whose eyes have not been opened to it. But having
built up the mystery, my other main aim is to remove it again by
explaining the solution.
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XIV
Preface
Explaining is a difficult art. You can explain something so that your
reader understands the words; and you can explain something so that
the reader feels it in the marrow of his bones. To do the latter, it
sometimes isn't enough to lay the evidence before the reader in a
dispassionate way. You have to become an advocate and use the tricks
of the advocate's trade. This book is not a dispassionate scientific
treatise. Other books on Darwinism are, and many of them are
excellent and informative and should be read in conjunction with this
one. Far from being dispassionate, it has to be confessed that in parts
this book is written with a passion which, in a professional scientific
journal, might excite comment. Certainly it seeks to inform, but it also
seeks to persuade and even - one can specify aims without
presumption - to inspire. I want to inspire the reader with a vision of
our own existence as, on the face of it, a spine-chilling mystery, and
simultaneously to convey the full excitement of the fact that it is a
mystery with an elegant solution which is within our grasp. More, I
want to persuade the reader, not just that the Darwinian world-view
happens to be true, but that it is the only known theory that could, in
principle, solve the mystery of our existence. This makes it a doubly
satisfying theory. A good case can be made that Darwinism is true, not
just on this planet but all over the universe wherever life may be found.
In one respect I plead to distance myself from professional advocates.
A lawyer or a politician is paid to exercise his passion and his persuasion
on behalf of a client or a cause in which he may not privately believe. I
have never done this and I never shall. I may not always be right, but I
care passionately about what is true and I never say anything that I do not
believe to be right. I remember being shocked when visiting a university
debating society to debate with creationists. At dinner after the debate, I
was placed next to a young woman who had made a relatively powerful
speech in favour of creationism. She clearly couldn't be a creationist, so I
asked her to tell me honestly why she had done it. She freely admitted
that she was simply practising her debating skills, and found it more
challenging to advocate a position in which she did not believe.
Apparently it is common practice in university debating societies for
speakers simply to be told on which side they are to speak. Their own
beliefs don't come into it. I had come a long way to perform the
disagreeable task of public speaking, because I believed in the truth of the
motion that I had been asked to propose. When I discovered that
members of the society were using the motion as a vehicle for playing
arguing games, I resolved to decline future invitations from debating
societies that encourage insincere advocacy on issues where scientific
truth is at stake.
Preface
xv
For reasons that are not entirely clear to me, Darwinism seems more
in need of advocacy than similarly established truths in other branches
of science. Many of us have no grasp of quantum theory, or Einstein's
theories of special and general relativity, but this does not in itself
lead us to oppose these theories! Darwinism, unlike 'Einsteinism',
seems to be regarded as fair game for critics with any degree of
ignorance. I suppose one trouble with Darwinism is that, as Jacques
Monod perceptively remarked, everybody thinks he understands it. It
is, indeed, a remarkably simple theory; childishly so, one would have
thought, in comparison with almost all of physics and mathematics. In
essence, it amounts simply to the idea that non-random reproduction,
where there is hereditary variation, has consequences that are
far-reaching if there is time for them to be cumulative. But we have
good grounds for believing that this simplicity is deceptive. Never
forget that, simple as the theory may seem, nobody thought of it until
Darwin and Wallace in the mid nineteenth century, nearly 200 years
after Newton's Principia, and more than 2,000 years after Eratosthenes
measured the Earth. How could such a simple idea go so long
undiscovered by thinkers of the calibre of Newton, Galileo, Descartes,
Leibnitz, Hume and Aristotle? Why did it have to wait for two
Victorian naturalists? What was wrong with philosophers and
mathematicians that they overlooked it? And how can such a powerful
idea go still largely unabsorbed into popular consciousness?
It is almost as if the human brain were specifically designed to
misunderstand Darwinism, and to find it hard to believe. Take, for
instance, the issue of 'chance', often dramatized as blind chance. The
great majority of people that attack Darwinism leap with almost
unseemly eagerness to the mistaken idea that there is nothing other
than random chance in it. Since living complexity embodies the very
antithesis of chance, if you think that Darwinism is tantamount to
chance you'll obviously find it easy to refute Darwinism! One of my
tasks will be to destroy this eagerly believed myth that Darwinism is a
theory of 'chance'. Another way in which we seem predisposed to
disbelieve Darwinism is that our brains are built to deal with events on
radically different timescales from those that characterize evolutionary change. We are equipped to appreciate processes that take seconds,
minutes, years or, at most, decades to complete. Darwinism is a theory
of cumulative processes so slow that they take between thousands and
millions of decades to complete. All our intuitive judgements of what
is probable turn out to be wrong by many orders of magnitude. Our
•well-tuned apparatus of scepticism and subjective probability-theory
misfires by huge margins, because it is tuned - ironically, by evolution
XVI
Preface
itself - to work within a lifetime of a few decades. It requires effort of
the imagination to escape from the prison of familiar timescale, an
effort that I shall try to assist.
A third respect in which our brains seem predisposed to resist
Darwinism stems from our great success as creative designers. Our
world is dominated by feats of engineering and works of art. We are
entirely accustomed to the idea that complex elegance is an indicator
of premeditated, Grafted design. This is probably the most powerful
reason for the belief, held by the vast majority of people that have ever
lived, in some kind of supernatural deity. It took a very large leap of the
imagination for Darwin and Wallace to see that, contrary to all
intuition, there is another way and, once you have understood it, a far
more plausible way, for complex 'design' to arise out of primeval
simplicity. A leap of the imagination so large that, to this day, many
people seem still unwilling to make it. It is the main purpose of this
book to help the reader to make this leap.
Authors naturally hope that their books will have lasting rather
than ephemeral impact. But any advocate, in addition to putting the
timeless part of his case, must also respond to contemporary advocates
of opposing, or apparently opposing, points of view. There is a risk that
some of these arguments, however hotly they may rage today, will
seem terribly dated in decades to come. The paradox has often been
noted that the first edition of The Origin of Species makes a better case
than the sixth. This is because Darwin felt obliged, in his later
editions, to respond to contemporary criticisms of the first edition,
criticisms which now seem so dated that the replies to them merely
get in the way, and in places even mislead. Nevertheless, the
temptation to ignore fashionable contemporary criticisms that one
suspects of being nine days' wonders is a temptation that should not be
indulged, for reasons of courtesy not just to the critics but to their
otherwise confused readers. Though I have my own private ideas on
which chapters of my book will eventually prove ephemeral for this
reason, the reader - and time - must judge.
I am distressed to find that some women friends (fortunately not
many) treat the use of the impersonal masculine pronoun as if it
showed intention to exclude them. If there were any excluding to be
done (happily there isn't) I think I would sooner exclude men, but
when I once tentatively tried referring to my abstract reader as 'she', a
feminist denounced me for patronizing condescension: I ought to say
'he-or-she', and 'his-or-her'. That is easy to do if you don't care about
language, but then if you don't care about language you don't deserve
readers of either sex. Here, I have returned to the normal conventions
Preface
xvii
of English pronouns. I may refer to the 'reader' as 'he', but I no more
think of my readers as specifically male than a French speaker thinks
of a table as female. As a matter of fact I believe I do, more often than
not, think of my readers as female, but that is my personal affair and I'd
hate to think that such considerations impinged on how I use my
native language.
Personal, too, are some of my reasons for gratitude. Those to whom I
cannot do justice will understand. My publishers saw no reason to
keep from me the identities of their referees (not 'reviewers' - true
reviewers, pace many Americans under 40, criticize books only after
they are published, when it is too late for the author to do anything
about it), and I have benefited greatly from the suggestions of
Krebs (again), John Durant, Graham Cairns-Smith, leffrey Levinton,
Michael Ruse, Anthony Hallam and David Pye. Richard Gregory
kindly criticized Chapter 12, and the final version has benefited from
its complete excision. Mark Ridley and Alan Grafen, now no longer
even officially my students, are, together with Bill Hamilton, the
leading lights of the group of colleagues with whom I discuss evolution
and from whose ideas I benefit almost daily. They, Pamela Wells, Peter
Atkins and John Dawkins have helpfully criticized various chapters for
me. Sarah Bunney made numerous improvements, and John Cribbin
corrected a major error. Alan Grafen and Will Atkinson advised on
computing problems, and the Apple Macintosh Syndicate of the
Zoology Department kindly allowed their laser printer to draw
biomorphs.
Once again I have benefited from the relentless dynamism with
which Michael Rodgers, now of Longman, carries all before him. He,
and Mary Cunnane of Norton, skilfully applied the accelerator (to my
morale) and the brake (to my sense of humour) when each was needed.
Part of the book was written during a sabbatical leave kindly granted
by the Department of Zoology and New College. Finally - a debt I
should have acknowledged in both my previous books - the Oxford
tutorial system and my many tutorial pupils in zoology over the years
have helped me to practise what few skills I may have in the difficult
art of explaining.
Richard Dawkins
Oxford, 1986
CHAPTER 1
EXPLAINING
THE VERY IMPROBABLE
We animals are the most complicated things in the known universe.
The universe that we know, of course, is a tiny fragment of the actual
universe. There may be yet more complicated objects than us on other
planets, and some of them may already know about us. But this doesn't
alter the point that I want to make. Complicated things, everywhere,
deserve a very special kind of explanation. We want to know how they
came into existence and why they are so complicated. The explanation, as I shall argue, is likely to be broadly the same for complicated things everywhere in the universe; the same for us, for
chimpanzees, worms, oak trees and monsters from outer space. On the
other hand, it will not be the same for what I shall call 'simple' things,
such as rocks, clouds, rivers, galaxies and quarks. These are the stuff of
physics. Chimps and dogs and bats and cockroaches and people and
worms and dandelions and bacteria and galactic aliens are the stuff of
biology.
The difference is one of complexity of design. Biology is the study of
complicated things that give the appearance of having been designed
for a purpose. Physics is the study of simple things that do not tempt us
to invoke design. At first sight, man-made artefacts like computers and
cars will seem to provide exceptions. They are complicated and
obviously designed for a purpose, yet they are not alive, and they are
made of metal and plastic rather than of flesh and blood. In this book
they will be firmly treated as biological objects.
The reader's reaction to this may be to ask, 'Yes, but are they really
biological objects?' Words are our servants, not our masters. For
different purposes we find it convenient to use words in different
senses. Most cookery books class lobsters as fish. Zoologists can
The Blind Watchmaker
become quite apoplectic about this, pointing out that lobsters could
with greater justice call humans fish, since fish are far closer kin to
humans than they are to lobsters. And, talking of justice and lobsters, I
understand that a court of law recently had to decide whether lobsters
were insects or 'animals' (it bore upon whether people should be
allowed to boil them alive). Zoologically speaking, lobsters are
certainly not insects. They are animals, but then so are insects and so
are we. There is little point in getting worked up about the way
different people use words (although in my nonprofessional life I am
quite prepared to get worked up about people who boil lobsters alive).
Cooks and lawyers need to use words in their own special ways, and so
do I in this book. Never mind whether cars and computers are 'really'
biological objects. The point is that if anything of that degree of
complexity were found on a planet, we should have no hesitation in
concluding that life existed, or had once existed, on that planet.
Machines are the direct products of living objects; they derive their
complexity and design from living objects, and they are diagnostic of
the existence of life on a planet. The same goes for fossils, skeletons
and dead bodies.
I said that physics is the study of simple things, and this, too, may
seem strange at first. Physics appears to be a complicated subject,
because the ideas of physics are difficult for us to understand. Our
brains were designed to understand hunting and gathering, mating and
child-rearing: a world of medium-sized objects moving in three dimensions at moderate speeds. We are ill-equipped to comprehend the
very small and the very large; things whose duration is measured in
picoseconds or gigayears; particles that don't have position; forces and
fields that we cannot see or touch, which we know of only because
they affect things that we can see or touch. We think that physics is
complicated because it is hard for us to understand, and because
physics books are full of difficult mathematics. But the objects that
physicists study are still basically simple objects. They are clouds of
gas or tiny particles, or lumps of uniform matter like crystals, with
almost endlessly repeated atomic patterns. They do not, at least by
biological standards, have intricate working parts. Even large physical
objects like stars consist of a rather limited array of parts, more or less
haphazardly arranged. The behaviour of physical, nonbiological objects
is so simple that it is feasible to use existing mathematical language to
describe it, which is why physics books are full of mathematics.
Physics books may be complicated, but physics books, like cars and
computers, are the product of biological objects - human brains. The
objects and phenomena that a physics book describes are simpler than
Explaining the very improbable
a single cell in the body of its author. And the author consists of
trillions of those cells, many of them different from each other, organized with intricate architecture and precision-engineering into a working machine capable of writing a book (my trillions are American, like
all my units: one American trillion is a million millions; an American
billion is a thousand millions). Our brains are no better equipped to
handle extremes of complexity than extremes of size and the other
difficult extremes of physics. Nobody has yet invented the
mathematics for describing the total structure and behaviour of such
an object as a physicist, or even of one of his cells. What we can do is
understand some of the general principles of how living things work,
and why they exist at all.
This was where we came in. We wanted to know why we, and all
other complicated things, exist. And we can now answer that question
in general terms, even without being able to comprehend the details of
the complexity itself. To take an analogy, most of us don't understand
in detail how an airliner works. Probably its builders don't comprehend it fully either: engine specialists don't in detail understand wings,
and wing specialists understand engines only vaguely. Wing specialists
don't even understand wings with full mathematical precision: they
can predict how a wing will behave in turbulent conditions, only by
examining a model in a wind tunnel or a computer simulation - the
sort of thing a biologist might do to understand an animal. But however incompletely we understand how an airliner works, we all understand by what general process it came into existence. It was designed
by humans on drawing boards. Then other humans made the bits from
the drawings, then lots more humans (with the aid of other machines
designed by humans) screwed, rivetted, welded or glued the bits
together, each in its right place. The process by which an airliner came
into existence is not fundamentally mysterious to us, because humans
built it. The systematic putting together of parts to a purposeful design
is something we know and understand, for we have experienced it at
first hand, even if only with our childhood Meccano or Erector set.
What about our own bodies? Each one of us is a machine, like an
airliner only much more complicated. Were we designed on a drawing
board too, and were our parts assembled by a skilled engineer? The
answer is no. It is a surprising answer, and we have known and understood it for only a century or so. When Charles Darwin first explained
the matter, many people either wouldn't or couldn't grasp it. I myself
flatly refused to believe Darwin's theory when I first heard about it as a
child. Almost everybody throughout history, up to the second half of
the nineteenth century, has firmly believed in the opposite - the
The Blind Watchmaker
Conscious Designer theory. Many people still do, perhaps because the
true, Darwinian explanation of our own existence is still, remarkably,
not a routine part of the curriculum of a general education. It is
certainly very widely misunderstood.
The watchmaker of my title is borrowed from a famous treatise by
the eighteenth-century theologian William Paley. His Natural
Theology - or Evidences of the Existence and Attributes of the Deity
Collected from the Appearances of Nature, published in 1802, is the
best-known exposition of the 'Argument from Design', always the
most influential of the arguments for the existence of a God. It is a
book that I greatly admire, for in his own time its author succeeded in
doing what I am struggling to do now. He had a point to make, he
passionately believed in it, and he spared no effort to ram it home
clearly. He had a proper reverence for the complexity of the living
world, and he saw that it demands a very special kind of explanation.
The only thing he got wrong - admittedly quite a big thing! - was the
explanation itself. He gave the traditional religious answer to the
riddle, but he articulated it more clearly and convincingly than
anybody had before. The true explanation is utterly different, and it
had to wait for one of the most revolutionary thinkers of all time,
Charles Darwin.
Paley begins Natural Theology with a famous passage:
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 for ever: 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 which I
had before given, that for anything 1 knew, the watch might have always
been there.
Paley here appreciates the difference between natural physical objects
like stones, and designed and manufactured objects like watches. He
goes on to expound the precision with which the cogs and spring's of a
watch are fashioned, and the intricacy with which they are put
together. If we found an object such as a watch upon a heath, even if we
didn't know how it had come into existence, its own precision and
intricacy of design would force us to conclude
that the watch must have had a maker: that there must have existed, at
some time, and at some place or other, an artificer or artificers, who formed
it for the purpose which we find it actually to answer, who comprehended
its construction, and designed its use.
Explaining the very
Nobody could reasonably dissent from this conclusion, Paley insists,
yet that is just what the atheist, in effect, does when he contemplates
the works of nature, for:
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.
Paley drives his point home with beautiful and reverent descriptions of
the dissected machinery of life, beginning with the human eye, a
favourite example which Darwin was later to use and which will
reappear throughout this book. Paley compares the eye with a designed
instrument such as a telescope, and concludes that 'there is precisely
the same proof that the eye was made for vision, as there is that the
telescope was made for assisting it'. The eye must have had a designer,
just as the telescope had.
Paley's argument is made with passionate sincerity and is informed
by the best biological scholarship of his day, but it is wrong, gloriously
and utterly wrong. The analogy between telescope and eye, between
watch and living organism, is false. All appearances to the contrary,
the only watchmaker in nature is the blind forces of physics, albeit
deployed in a very special way. A true watchmaker has foresight: he
designs his cogs and springs, and plans their interconnections, with a
future purpose in his mind's eye. Natural selection, the blind, unconscious, automatic process which Darwin discovered, and which we
now know is the explanation for the existence and apparently purposeful form of all life, has no purpose in mind. It has no mind and no
mind's eye. It does not plan for the future. It has no vision, no foresight,
no sight at all. If it can be said to play the role of watchmaker in
.nature, it is the blind watchmaker.
I shall explain all this, and much else besides. But one thing I shall
not do is belittle the wonder of the living 'watches' that so inspired
Paley. On the contrary, I shall try to illustrate my feeling that here
Paley could have gone even further. When it comes to feeling awe over
living 'watches' I yield to nobody. I feel more in common with the
Reverend William Paley than I do with the distinguished modern
philosopher, a well-known atheist, with whom I once discussed the
matter at dinner. I said that I could not imagine being an atheist at any
time before 1859, when Darwin's Origin of Species was published.
'What about Hume?', replied the philosopher. 'How did Hume explain
the organized complexity of the living world?', I asked. 'He didn't', said
the philosopher. 'Why does it need any special explanation?'
The Blind Watchmaker
Paley knew that it needed a special explanation; Darwin knew it,
and I suspect that in his heart of hearts my philosopher companion
knew it too. In any case it will be my business to show it here. As for
David Hume himself, it is sometimes said that that great Scottish
philosopher disposed of the Argument from Design d century before
Darwin. But what Hume did was criticize the logic of using apparent
design in nature as positive evidence for the existence of a God. He did
not offer any alternative explanation for apparent design, but left the
question open. An atheist before Darwin could have said, following
Hume: 'I have no explanation for complex biological design. All I know
is that Cod isn't a good explanation, so we must wait and hope that
somebody comes up with a better one.' I can't help feeling that such a
position, though logically sound, would have left one feeling pretty
unsatisfied, and that although atheism might have been logically
tenable before Darwin, Darwin made it possible to be an intellectually
fulfilled atheist. I like to think that Hume would agree, but some of his
writings suggest that he underestimated the complexity and beauty of
biological design. The boy naturalist Charles Darwin could have
shown him a thing or two about that, but Hume had been dead 40 years
when Darwin enrolled in Hume's university of Edinburgh.
I have talked glibly of complexity, and of apparent design, as though
it were obvious what these words mean. In a sense it is obvious - most
people have an intuitive idea of what complexity means. But these
notions, complexity and design, are so pivotal to this book that I must
try to capture a little more precisely, in words, our feeling that there is
something special about complex, and apparently designed things.
So, what is a complex thing? How should we recognize it? In what
sense is it true to say that a watch or an airliner or an earwig or a person
is complex, but the moon is simple? The first point that might occur to
us, as a necessary attribute of a complex thing, is that it has a
heterogeneous structure. A pink milk pudding or blancmange is simple
in the sense that, if we slice it in two, the two portions will have the
same internal constitution: a blancmange is homogeneous. A car is
heterogeneous: unlike a blancmange, almost any portion of the car is
different from other portions. Two times half a car does not make a car.
This will often amount to saying that a complex object, as opposed to a
simple one, has many parts, these parts being of more than one kind.
Such heterogeneity, or 'many-partedness', may be a necessary condition, but it is not sufficient. Plenty of objects are many-parted and
heterogeneous in internal structure, without being complex in the
sense in which I want to use the term. Mont Blanc, for instance,
consists of many different kinds of rock, all jumbled together in such a
Explaining the very improbable
way that, if you sliced the mountain anywhere, the two portions would
differ from each other in their internal constitution. Mont Blanc has a
heterogeneity of structure not possessed by a blancmange, but it is still
not complex in the sense in which a biologist uses the term.
Let us try another tack in our quest for a definition of complexity,
and make use of the mathematical idea of probability. Suppose we try
out the following definition: a complex thing is something whose
constituent parts are arranged in a way that is unlikely to have arisen
by chance alone. To borrow an analogy from an eminent astronomer, if
you take the parts of an airliner and jumble them up at random, the
likelihood that you would happen to assemble a working Boeing is
vanishingly small. There are billions of possible ways of putting
together the bits of an airliner, and only one, or very few, of them
would actually be an airliner. There are even more ways of putting
together the scrambled parts of a human.
This approach to a definition of complexity is promising, but
something more is still needed. There are billions of ways of throwing
together the bits of Mont Blanc, it might be said, and only one of them
is Mont Blanc. So what is it that makes the airliner and the human
complicated, if Mont Blanc is simple? Any old jumbled collection of
parts is unique and, with hindsight, is as improbable as any other. The
scrap-heap at an aircraft breaker's yard is unique. No two scrap-heaps
are the same. If you start throwing fragments of aeroplanes into heaps,
the odds of your happening to hit upon exactly the same arrangement
of junk twice are just about as low as the odds of your throwing
together a working airliner. So, why don't we say that a rubbish dump,
or Mont Blanc, or the moon, is just as complex as an aeroplane or a dog,
because in all these cases the arrangement of atoms is 'improbable'?
The combination lock on my bicycle has 4,096 different positions.
Every one of these is equally 'improbable' in the sense that, if you spin
the wheels at random, every one of the 4,096 positions is equally
unlikely to turn up. I can spin the wheels at random, look at whatever
number is displayed and exclaim with hindsight: 'How amazing. The
odds against that number appearing are 4,096:1. A minor miracle!'
That is equivalent to regarding the particular arrangement of rocks in a
mountain, or of bits of metal in a scrap-heap, as 'complex'. But one of
those 4,096 wheel positions really is interestingly unique: the combination 1207 is the only one that opens the lock. The uniqueness of
1207 has nothing to do with hindsight: it is specified in advance by the
manufacturer. If you spun the wheels at random and happened to hit
1207 first time, you would be able to steal the bike, and it would seem
a minor miracle. If you struck lucky on one of those multi-dialled
The Blind
combination locks on bank safes, it would seem a very major miracle,
for the odds against it are many millions to one, and you would be able
to steal a fortune.
Now, hitting upon the lucky number that opens the bank's safe is
the equivalent, in our analogy, of hurling scrap metal around at
random and happening to assemble a Boeing 747. Of all the millions of
unique and, with hindsight equally improbable, positions of the combination lock, only one opens the lock. Similarly, of all the millions of
unique and, with hindsight equally improbable, arrangements of a
heap of junk, only one (or very few) will fly. The uniqueness of the
arrangement that flies, or that opens the safe, is nothing to do with
hindsight. It is specified in advance. The lock-manufacturer fixed the
combination, and he has told the bank manager. The ability to fly is a
property of an airliner that we specify in advance. If we see a plane in
the air we can be sure that it was not assembled by randomly throwing
scrap metal together, because we know that the odds against a random
conglomeration's being able to fly are too great.
Now, if you consider all possible ways in which the rocks of Mont
Blanc could have been thrown together, it is true that only one of them
would make Mont Blanc as we know it. But Mont Blanc as we know it
is defined with hindsight. Any one of a very large number of ways of
throwing rocks together would be labelled a mountain, and might have
been named Mont Blanc. There is nothing special about the particular
Mont Blanc that we know, nothing specified in advance, nothing
equivalent to the plane taking off, or equivalent to the safe door
swinging open and the money tumbling out.
What is the equivalent of the safe door swinging open, or the plane
flying, in the case of a living body? Well, sometimes it is almost
literally the same. Swallows fly. As we have seen, it isn't easy to throw
together a flying machine. If you took all the cells of a swallow and put
them together at random, the chance that the resulting object would
fly is not, for everyday purposes, different from zero. Not all living
things fly, but they do other things that are just as improbable, and just
as specifiable in advance. Whales don't fly, but they do swim, and
swim about as efficiently as swallows fly. The chance that a random
conglomeration of whale cells would swim, let alone swim as fast and
efficiently as a whale actually does swim, is negligible.
At this point, some hawk-eyed philosopher (hawks have very acute
eyes — you couldn't make a hawk's eye by throwing lenses and lightsensitive cells together at random) will start mumbling something
about a circular argument. Swallows fly but they don't swim; and
whales swim but they don't fly. It is with hindsight that we decide
Explaining the very improbable
whether to judge the success of our random conglomeration as a
swimmer or as a flyer. Suppose we agree to judge its success as an Xer,
and leave open exactly what X is until we have tried throwing cells
together. The random lump of cells might turn out to be an efficient
burrower like a mole or an efficient climber like a monkey. It might be
very good at wind-surfing, or at clutching oily rags, or at walking in
ever decreasing circles until it vanished. The list could go on and on.
Or could it?
If the list really could go on and on, my hypothetical philosopher
might have a point. If, no matter how randomly you threw matter
around, the resulting conglomeration could often be said, with
hindsight, to be good for something, then it would be true to say that I
cheated over the swallow and the whale. But biologists can be much
more specific than that about what would constitute being 'good for
something'. The minimum requirement for us to recognize an object
as an animal or plant is that it should succeed in making a living of
some sort (more precisely that it, or at least some members of its kind,
should live long enough to reproduce). It is true that there are quite a
number of ways of making a living - flying, swimming, swinging
through the trees, and so on. But, however many ways there may be of
being alive, it is certain that there are vastly more ways of
dead,
or rather not alive. You may throw cells together at random, over and
over again for a billion years, and not once will you get a conglomeration that flies or swims or burrows or runs, or does anything,
even badly, that could remotely be construed as working to keep itself
alive.
This has been quite a long, drawn-out argument, and it is time to
remind ourselves of how we got into it in the first place. We were
looking for a precise way to express what we mean when we refer to
something as complicated. We were trying to put a finger on what it is
that humans and moles and earthworms and airliners and watches
have in common with each other, but not with blancmange, or Mont
Blanc, or the moon. The answer we have arrived at is that complicated
things have some quality, specifiable in advance, that is highly unlikely to have been acquired by random chance alone. In the case of
living things, the quality that is specified in advance is, in some sense,
'proficiency'; either proficiency in a particular ability such as flying, as
an aero-engineer might admire it; or proficiency in something more
general, such as the ability to stave off death, or the ability to propagate
genes in reproduction.
Staving off death is a thing that you have to work at. Left to itself and that is what it is when it dies - the body tends to revert to a state of
10
The Blind Watchmaker
equilibrium with its environment. If you measure some quantity such
as the temperature, the acidity, the water content or the electrical
potential in a living body, you will typically find that it is markedly
different from the corresponding measure in the surroundings. Our
bodies, for instance, are usually hotter than our surroundings, and in
cold climates they have to work hard to maintain the differential.
When we die the work stops, the temperature differential starts to
disappear, and we end up the same temperature as our surroundings.
Not all animals work so hard to avoid coming into equilibrium with
their surrounding temperature, but all animals do some comparable
work. For instance, in a dry country, animals and plants work to
maintain the fluid content of their cells, work against a natural
tendency for water to flow from them into the dry outside world. If
they fail they die. More generally, if living things didn't work actively
to prevent it, they would eventually merge into their surroundings,
and cease to exist as autonomous beings. That is what happens when
they die.
With the exception of artificial machines, which we have already
agreed to count as honorary living things, nonliving things don't work
in this sense. They accept the forces that tend to bring them into
equilibrium with their surroundings. Mont Blanc, to be sure, has existed for a long time, and probably will exist for a while yet, but it does
not work to stay in existence. When rock comes to rest under the
influence of gravity it just stays there. No work has to be done to keep
it there. Mont Blanc exists, and it will go on existing until it wears
away or an earthquake knocks it over. It doesn't take steps to repair
wear and tear, or to right itself when it is knocked over, the way a
living body does. It just obeys the ordinary laws of physics.
Is this to deny that living things obey the laws of physics? Certainly
not. There is no reason to think that the laws of physics are violated in
living matter. There is nothing supernatural, no 'life force' to rival the
fundamental forces of physics. It is just that if you try to use the laws of
physics, in a naive way, to understand the behaviour of a whole living
body, you will find that you don't get very far. The body is a complex
thing with many constituent parts, and to understand its behaviour
you must apply the laws of physics to its parts, not to the whole. The
behaviour of the body as a whole will then emerge as a consequence of
interactions of the parts.
Take the laws of motion, for instance. If you throw a dead bird into
the air it will describe a graceful parabola, exactly as physics books say
it should, then come to rest on the ground and stay there. It behaves as
a solid body of a particular mass and wind resistance ought to behave.
Explaining the very improbable
11
But if you throw a live bird in the air it will not describe a parabola and
come to rest on the ground. It will fly away, and may not touch land
this side of the county boundary. The reason is that it has muscles
which work to resist gravity and other physical forces bearing upon the
whole body. The laws of physics are being obeyed within every cell of
the muscles. The result is that the muscles move the wings in such a
way that the bird stays aloft. The bird is not violating the law of
gravity. It is constantly being pulled downwards by gravity, but its
wings are performing active work - obeying laws of physics within its
muscles - to keep it aloft in spite of the force of gravity. We shall think
that it defies a physical law if we are naive enough to treat it simply as
a structureless lump of matter with a certain mass and wind resistance. It is only when we remember that it has many internal parts, all
obeying laws of physics at their own level, that we understand the
behaviour of the whole body. This is not, of course, a peculiarity of
living things. It applies to all man-made machines, and potentially
applies to any complex, many-parted object.
This brings me to the final topic that I want to discuss in this rather
philosophical chapter, the problem of what we mean by explanation.
We have seen what we are going to mean by a complex thing. But what
kind of explanation will satisfy us if we wonder how a complicated
machine, or living body, works? The answer is the one that we arrived
at in the previous paragraph. If we wish to understand how a machine
or living body works, we look to its component parts and ask how they
interact with each other. If there is a complex thing that we do not yet
understand, we can come to understand it in terms of simpler parts
that we do already understand.
If I ask an engineer how a steam engine works, I have a pretty fair
idea of the general kind of answer that would satisfy me. Like
Huxley I should definitely not be impressed if the engineer said it was
propelled by 'force locomotif. And if he started boring on about the
whole being greater than the sum of its parts, I would interrupt him:
'Never mind about that, tell me how it works.' What I would want to
hear is something about how the parts of an engine interact with each
other to produce the behaviour of the whole engine. I would initially be
prepared to accept an explanation in terms of quite large subcomponents, whose own internal structure and behaviour might be quite
complicated and, as yet, unexplained. The units of an initially satisfying explanation could have names like fire-box, boiler, cylinder,
piston, steam governor. The engineer would assert, without explanation initially, what each of these units does. I would accept this
for the moment, without asking how each unit does its own particular
12
The Blind Watchmaker
thing. Given that the units each do their particular thing, I can then
understand how they interact to make the whole engine move.
Of course, I am then at liberty to ask how each part works. Having
previously accepted the fact that the steam governor regulates the flow
of steam, and having used this fact in my understanding of the behaviour of the whole engine, I now turn my curiosity on the steam
governor itself. I now want to understand how it achieves its own
behaviour, in terms of its own internal parts. There is a hierarchy of
subcomponents within components. We explain the behaviour of a
component at any given level, in terms of interactions between subcomponents whose own internal organization, for the moment, is
taken for granted. We peel our way down the hierarchy, until we reach
units so simple that, for everyday purposes, we no longer feel the need
to ask questions about them. Rightly or wrongly for instance, most of
us are happy about the properties of rigid rods of iron, and we are
prepared to use them as units of explanation of more complex
machines that contain them.
Physicists, of course, do not take iron rods for granted. They ask
why they are rigid, and they continue the hierarchical peeling for
several more layers yet, down to fundamental particles and quarks. But
life is too short for most of us to follow them. For any given level of
complex organization, satisfying explanations may normally be
attained if we peel the hierarchy down one or two layers from our
starting layer, but not more. The behaviour of a motor car is explained
in terms of cylinders, carburettors and sparking plugs. It is true that
each one of these components rests atop a pyramid of explanations at
lower levels. But if you asked me how a motor car worked you would
think me somewhat pompous if I answered in terms of Newton's laws
and the laws of thermodynamics, and downright obscurantist if I
answered in terms of fundamental particles. It is doubtless true that at
bottom the behaviour of a motor car is to be explained in terms of
interactions between fundamental particles. But it is much more
useful to explain it in terms of interactions between pistons, cylinders
and sparking plugs.
The behaviour of a computer can be explained in terms of interactions between semiconductor electronic gates, and the behaviour of
these, in turn, is explained by physicists at yet lower levels. But, for
most purposes, you would in practice be wasting your time if you tried
to understand the behaviour of the whole computer at either of those
levels. There are too many electronic gates and too many interconnections between them. A satisfying explanation has to be in terms of
a manageably small number of interactions. This is why, if we want to
Explaining the very improbable
13
understand the workings of computers, we prefer a preliminary explanation in terms of about half a dozen major subcomponents memory, processing mill, backing store, control unit, input-output
handler, etc. Having grasped the interactions between the half-dozen
major components, we then may wish to ask questions about the
internal organization- of these major components. Only specialist engineers are likely to go down to the level of AND gates and NOR gates,
and only physicists will go down further, to the level of how electrons
behave in a semiconducting medium.
For those that like '-ism' sorts of names, the aptest name for my
approach to understanding how things work is probably 'hierarchical
reductionism'. If you read trendy intellectual magazines, you may have
noticed that 'reductionism' is one of those things, like sin, that is only
mentioned by people who are against it. To call oneself a reductionist
will sound, in some circles, a bit like admitting to eating babies. But,
just as nobody actually eats babies, so nobody is really a reductionist in
any sense worth being against. The nonexistent reductionist - the sort
that everybody is against, but who exists only in their imaginations tries to explain complicated things directly in terms of the smallest
parts, even, in some extreme versions of the myth, as the sum of the
parts! The hierarchical reductionist, on the other hand, explains a
complex entity at any particular level in the hierarchy of organization,
in terms of entities only one level down the hierarchy; entities which,
themselves, are likely to be complex enough to need further reducing
to their own component parts; and so on. It goes without saying though the mythical, baby-eating reductionist is reputed to deny this that the kinds of explanations which are suitable at high levels in the
hierarchy are quite different from the kinds of explanations which are
suitable at lower levels. This was the point of explaining cars in terms
of carburettors rather than quarks. But the hierarchical reductionist
believes that carburettors are explained in terms of smaller units . . .,
which are explained in terms of smaller units . . . , which are
ultimately explained in terms of the smallest of fundamental particles.
Reductionism, in this sense, is just another name for an honest desire
to understand how things work.
We began this section by asking what kind of explanation for complicated things would satisfy us. We have just considered the question
from the point of view of mechanism: how does it work? We concluded
that the behaviour of a complicated thing should be explained in terms
of interactions between its component parts, considered as successive
layers of an orderly hierarchy. But another kind of question is how the
complicated thing came into existence in the first place. This is the
14
The Blind Watchmaker
question that this whole book is particularly concerned with, so I won't
say much more about it here. I shall just mention that the same general
principle applies as for understanding mechanism. A complicated
thing is one whose existence we do not feel inclined to take for
granted, because it is too 'improbable'. It could not have come into
existence in a single act of chance. We shall explain its coming into
existence as a consequence of gradual, cumulative, step-by-step transformations from simpler things, from primordial objects sufficiently
simple to have come into being by chance. Just as 'big-step reductionism' cannot work as an explanation of mechanism, and must
be replaced by a series of small step-by-step peelings down through the
hierarchy, so we can't explain a complex thing as originating in a
single step. We must again resort to a series of small steps, this time
arranged sequentially in time.
In his beautifully written book, The Creation, the Oxford physical
chemist Peter Atkins begins:
I shall take your mind on a journey. It is a journey of comprehension, taking
us to the edge of space, time, and understanding. On it I shall argue that
there is nothing that cannot be understood, that there is nothing that
cannot be explained, and that everything is extraordinarily simple . .. A
great deal of the universe does not need any explanation. Elephants, for
instance. Once molecules have learnt to compete and to create other
molecules in their own image, elephants, and things resembling elephants,
will in due course be found roaming through the countryside.
Atkins assumes the evolution of complex things - the subject matter
of this book - to be inevitable once the appropriate physical conditions
have been set up. He asks what the minimum necessary physical
conditions are, what is the minimum amount of design work that a
very lazy Creator would have to do, in order to see to it that the
universe and, later, elephants and other complex things, would one day
come into existence. The answer, from his point of view as a physical
scientist, is that the Creator could be infinitely lazy. The fundamental
original units that we need to postulate, in order to understand the
coming into existence of everything, either consist of literally nothing
(according to some physicists), or (according to other physicists) they
are units of the utmost simplicity, far too simple to need anything so
grand as deliberate Creation.
Atkins says that elephants and complex things do not need any
explanation. But that is because he is a physical scientist, who takes
for granted the biologists' theory of evolution. He doesn't really mean
that elephants don't need an explanation; rather that he is satisfied
that biologists can explain elephants, provided they are allowed to take
Explaining the very improbable
15
certain facts of physics for granted. His task as a physical scientist,
therefore, is to justify our taking those facts for granted. This he
succeeds in doing. My position is complementary. I am a biologist. I
take the facts of physics, the facts of the world of simplicity, for
granted. If physicists still don't agree over whether those simple facts
are yet understood, that is not my problem. My task is to explain
elephants, and the world of complex things, in terms of the simple
things that physicists either understand, or are working on. The physicist's problem is the problem of ultimate origins and ultimate natural
laws. The biologist's problem is the problem of complexity. The
biologist tries to explain the workings, and the coming into existence,
of complex things, in terms of simpler things. He can regard his task as
done when he has arrived at entities so simple that they can safely be
handed over to physicists.
I am aware that my characterization of a complex object - statistically improbable in a direction that is specified not with hindsight may seem idiosyncratic. So, too, may seem my characterization of
physics as the study of simplicity. If you prefer some other way of
defining complexity, I don't care and I would be happy to go along with
your definition for the sake of discussion. But what I do care about is
that, whatever we choose to call the quality of being statisticallyimprobable-in-a-direction-specified-without-hindsight, it is an important quality that needs a special effort of explanation. It is the quality
that characterizes biological objects as opposed to the objects of physics. The kind of explanation we come up with must not contradict the
laws of physics. Indeed it will make use of the laws of physics, and
nothing more than the laws of physics. But it will deploy the laws of
physics in a special way that is not ordinarily discussed in physics
textbooks. That special way is Darwin's way. I shall introduce its
fundamental essence in Chapter 3 under the title of cumulative selection.
Meanwhile I want to follow Paley in emphasizing the magnitude of
the problem that our explanation faces, the sheer hugeness of biological complexity and the beauty and elegance of biological design. Chapter 2 is an extended discussion of a particular example, 'radar' in bats,
discovered long after Paley's time. And here, in this chapter, I have
placed an illustration (Figure 1) — how Paley would have loved the
electron microscope! - of an eye together with two successive 'zoomings in' on detailed portions. At the top of the figure is a section
through an eye itself. This level of magnification shows the eye as an
optical instrument. The resemblance to a camera is obvious. The iris
diaphragm is responsible for constantly varying the aperture, the / stop.
The Blind Watchmaker
Transparent jelly
Explaining the very improbable
17
The lens, which is really only part of a compound lens system, is
responsible for the variable part of the focusing. Focus is changed by
squeezing the lens with muscles (or in chameleons by moving the lens
forwards or backwards, as in a man-made camera). The image falls on
the retina at the back, where it excites photocells.
The middle part of Figure 1 shows a small section of the retina
enlarged. Light comes from the left. The light-sensitive cells ('photocells') are not the first thing the light hits, but they are buried inside
and facing away from the light. This odd feature is mentioned again
later. The first thing the light hits is, in fact, the layer of ganglion cells
which constitute the 'electronic interface' between the photocells and
the brain. Actually the ganglion cells are responsible for preprocessing
the information in sophisticated ways before relaying it to the brain,
and in some ways the word 'interface' doesn't do justice to this.
'Satellite computer' might be a fairer name. Wires from the ganglion
cells run along the surface of the retina to the 'blind spot', where they
dive through the retina to form the main trunk cable to the brain, the
optic nerve. There are about three million ganglion cells in the 'electronic interface', gathering data from about 125 million photocells.
At the bottom of the figure is one enlarged photocell, a rod. As you
look at the fine architecture of this cell, keep in mind the fact that all
that complexity is repeated 125 million times in each retina. And
comparable complexity is repeated trillions of times elsewhere in the
body as a whole. The figure of 125 million photocells is about 5,000
times the number of separately resolvable points in a good-quality
magazine photograph. The folded membranes on the right of the illustrated photocell are the actual light-gathering structures. Their layered
form increases the photocell's efficiency in capturing photons, the
fundamental particles of which light is made. If a photon is not caught
by the first membrane, it may be caught by the second, and so on. As a
result of this, some eyes are capable of detecting a single photon. The
fastest and most sensitive film emulsions available to photographers
need about 25 times as many photons in order to detect a point of light.
The lozenge-shaped objects in the middle section of the cell are mostly
mitochondria. Mitochondria are found not just in photocells, but in
most other cells. Each one can be thought of as a chemical factory
which, in the course of delivering its primary product of usable energy,
processes more than 700 different chemical substances, in long, interweaving assembly-lines strung out along the surface of its intricately
folded internal membranes. The round globule at the left of Figure 1 is
the nucleus. Again, this is characteristic of all animal and plant cells.
Each nucleus, as we shall see in Chapter 5, contains a digitally coded
18
The Blind Watchmaker
database larger, in information content, than all 30
of the
Encyclopaedia Britannica put together. And this figure is for each cell,
not all the cells of a body put together.
The rod at the base of the picture is one single cell. The total
number of cells in the body (of a human) is about 10 trillion. When you
eat a steak, you are shredding the equivalent of more than 100 billion
copies of the Encyclopaedia
CHAPTER 2
GOOD DESIGN
Natural selection is the blind watchmaker, blind because it does not
see ahead, does not plan consequences, has no purpose in view. Yet the
living results of natural selection overwhelmingly impress us with the
appearance of design as if by a master watchmaker, impress us with
the illusion of design and planning. The purpose of this book is to
resolve this paradox to the satisfaction of the reader, and the purpose of
this chapter is further to impress the reader with the power of the
illusion of design. We shall look at a particular example and shall
conclude that, when it comes to complexity and beauty of design,
Paley hardly even began to state the case.
We may say that a living body or organ is well designed if it has
attributes that an intelligent and knowledgeable engineer might have
built into it in order to achieve some sensible purpose, such as flying,
swimming, seeing, eating, reproducing, or more generally promoting
the survival and replication of the organism's genes. It is not necessary
to suppose that the design of a body or organ is the best that an
engineer could conceive of. Often the best that one engineer can do is,
in any case, exceeded by the best that another engineer can do,
especially another who lives later in the history of technology. But any
engineer can recognize an object that has been designed, even poorly
designed, for a purpose, and he can usually work out what that purpose
is just by looking at the structure of the object. In Chapter 1 we
bothered ourselves mostly with philosophical aspects. In this chapter, I
shall develop a particular factual example that I believe would impress
any engineer, namely sonar ('radar') in bats. In explaining each point, I
shall begin by posing a problem that the living machine faces; then I
shall consider possible solutions to the problem that a sensible
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