Sample text for The ancestor's tale : a pilgrimage to the dawn of evolution / Richard Dawkins.


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THE CONCEIT OF HINDSIGHT

History has been described as one damn
thing after another. The remark can be seen as a
warning against a pair of temptations but, duly warned, I shall cautiously
flirt with both. First, the historian is tempted to scour the past for patterns
that repeat themselves; or at least, following Mark Twain, to seek
reason and rhyme for everything. This appetite for pattern affronts those
who insist that, as Mark Twain will also be found to have said, "History is
usually a random, messy affair", going nowhere and following no rules.
The second connected temptation is the vanity of the present: of seeing
the past as aimed at our own time, as though the characters in history"s
play had nothing better to do with their lives than foreshadow us.
Under names that need not trouble us, these are live issues in human
history and they arise with greater force, and no greater agreement, on
the longer timescale of evolution. Evolutionary history can be represented
as one damn species after another. But many biologists will join
me in finding this an impoverished view. Look at evolution that way and
you miss most of what matters. Evolution rhymes, patterns recur. And
this doesn"t just happen to be so. It is so for well-understood reasons:
Darwinian reasons mostly, for biology, unlike human history or even
physics, already has its grand unifying theory, accepted by all informed
practitioners, though in varying versions and interpretations. In writing
evolutionary history I do not shrink from seeking patterns and principles,
but I try to be careful about it.

What of the second temptation, the conceit of hindsight, the idea that
the past works to deliver our particular present? The late Stephen Jay
Gould rightly pointed out that a dominant icon of evolution in popular
mythology, a caricature almost as ubiquitous as lemmings jumping over
cliffs (and that myth is false too), is a shambling file of simian ancestors,
rising progressively in the wake of the erect, striding, majestic figure of
Homo sapiens sapiens: man as evolution"s last word (and in this context it
always is man rather than woman); man as what the whole enterprise is
pointing towards; man as a magnet, drawing evolution from the past towards
his eminence.

There is a physicist"s version which is less obviously vainglorious and
which I should mention in passing. This is the "anthropic" notion that the
very laws of physics themselves, or the fundamental constants of the
universe,
are a carefully tuned put-up job, calculated to bring humanity
eventually into existence. It is not necessarily founded on vanity. It
doesn"t have to mean that the universe was deliberately made in order
that we should exist. It need mean only that we are here, and we could
not be in a universe that lacked the capability of producing us. As physicists
have pointed out, it is no accident that we see stars in our sky, for
stars are a necessary part of any universe capable of generating us. Again,
this does not imply that stars exist in order to make us. It is just that
without stars there would be no atoms heavier than lithium in the periodic
table, and a chemistry of only three elements is too impoverished to
support life. Seeing is the kind of activity that can go on only in the kind
of universe where what you see is stars.

But there is a little more that needs to be said. Granted the trivial
fact that our presence requires physical laws and constants capable of
producing us, the existence of such potent ground rules may still seem
tantalisingly improbable. Depending upon their assumptions, physicists
may reckon that the set of possible universes vastly outnumbers that subset
whose laws and constants allowed physics to mature, via stars into
chemistry and via planets into biology. To some, this means that the
laws and constants must have been deliberately premeditated from the
start (although it baffles me why anybody regards this as an explanation
for anything, given that the problem so swiftly regresses to the larger one
of explaining the existence of the equally fine-tuned and improbable
Premeditator).

Other physicists are less confident that the laws and constants were
free to vary in the first place. When I was little it was not obvious to me
why five times eight had to give the same result as eight times five. I
accepted it as one of those facts that grownups assert. Only later did I
understand, perhaps through visualising rectangles, why such pairs of
multiplications are not free to vary independently of one another. We
understand that the circumference and the diameter of a circle are not
independent, otherwise we might feel tempted to postulate a plethora of
possible universes, each with a different value of. Perhaps, argue some
physicists such as the Nobel Prize-winning theorist StevenWeinberg, the
fundamental constants of the universe, which at present we treat as
independent
of one another, will in some Grand Unified fullness of time be
understood to have fewer degrees of freedom than we now imagine.
Maybe there is only one way for a universe to be. That would undermine
the appearance of anthropic coincidence.

Other physicists, including Sir Martin Rees, the present Astronomer
Royal, accept that there is a real coincidence in need of explanation, and
explain it by postulating many actual universes existing in parallel, mutually
incommunicado, each with its own set of laws and constants.* Obviously
we, who find ourselves reflecting upon such things, must be in
one of those universes, however rare, whose laws and constants are capable
of evolving us.

The theoretical physicist Lee Smolin added an ingenious Darwinian
spin which reduces the apparent statistical improbability of our existence.
In Smolin"s model, universes give birth to daughter universes,
which vary in their laws and constants. Daughter universes are born in
black holes produced by a parent universe, and they inherit its laws and
constants but with some possibility of small random change -- "mutation".
Those daughter universes that have what it takes to reproduce (last
long enough to make black holes, for instance) are, of course, the universes
that pass on their laws and constants to their daughters. Stars are
precursors to black holes which, in the Smolin model, are the birth
events. So universes that have what it takes to make stars are favoured in
this cosmic Darwinism. The properties of a universe that furnish this gift
to the future are the self-same properties that incidentally lead to the

* This "many universes" idea is not to be confused (though it often is) with
Hugh Everett"s "many worlds" interpretation of quantum theory, brilliantly
advocated by David Deutsch in The Fabric of Reality. The resemblance
between the two theories is superficial and meaningless. Both theories could
be true, or neither, or one, or the other. They were proposed to answer
completely different problems. In the Everett theory, the different universes
don"t differ in their fundamental constants. But it is the entire point of the
theory we are here considering that the different universes have different
fundamental constants.

manufacture of large atoms, including vital carbon atoms. Not only do
we live in a universe that is capable of producing life. Successive generations
of universes progressively evolve to become increasingly the sort of
universe that, as a by-product, is capable of producing life.

The logic of the Smolin theory is bound to appeal to a Darwinian, indeed
to anyone of imagination, but as for the physics I am not qualified
to judge. I cannot find a physicist to condemn the theory as definitely
wrong -- the most negative thing they will say is that it is superfluous.
Some, as we saw, dream of a final theory in whose light the alleged finetuning
of the universe will turn out to be a delusion anyway. Nothing we
know rules out Smolin"s theory, and he claims for it the merit -- which
scientists rate more highly than many laymen appreciate -- of testability.
His book is The Life of the Cosmos and I recommend it.

But that was a digression about the physicist"s version of the conceit
of hindsight. The biologist"s version is easier to dismiss since Darwin,
though harder before him, and it is our concern here. Biological evolution
has no privileged line of descent and no designated end. Evolution
has reached many millions of interim ends (the number of surviving
species at the time of observation), and there is no reason other than
vanity -- human vanity as it happens, since we are doing the talking -- to
designate any one as more privileged or climactic than any other.
This doesn"t mean, as I shall continue to argue, that there is a total
dearth of reasons or rhymes in evolutionary history. I believe there are
recurring patterns. I also believe, though this is more controversial today
than it once was, that there are senses in which evolution may be said to
be directional, progressive and even predictable. But progress is emphatically
not the same thing as progress towards humanity, and we must live
with a weak and unflattering sense of the predictable. The historian must
beware of stringing together a narrative that seems, even to the smallest
degree, to be homing in on a human climax.

A book in my possession (in the main a good book, so I shall not
name and shame it) provides an example. It is comparing Homo habilis
(a human species, probably ancestral to us) with its predecessors the
australopithecines.*

What the book says is that Homo habilis was "consider-


* The laws of zoological nomenclature follow strict precedence, and I fear
there is no hope of changing the name Australopithecus to something less
confusing to the contemporary majority who lack a classical education. It has
nothing to do with Australia. No member of the genus has ever been found
outside Africa. Australo simply means southern. Australia is the great
southern continent, the Aurora australis is the southern equivalent of the
Aurora borealis (boreal means northern), and Australopithecus was
first found in south Africa, in the person of the Taung child.


ably more evolved than the Australopithecines".More evolved? What can
this mean but that evolution is moving in some pre-specified direction?
The book leaves us in no doubt of what the presumed direction is. "The
first signs of a chin are apparent." "First" encourages us to expect second
and third signs, towards a "complete" human chin. "The teeth start to resemble
ours . . ."As if those teeth were the way they were, not because it
suited the habiline diet but because they were embarking upon the road
towards becoming our teeth. The passage ends with a telltale remark
about a later species of extinct human, Homo erectus:
Although their faces are still different from ours, they have a much
more human look in their eyes. They are like sculptures in the
making, 'unfinished' works.

In the making? Unfinished? Only with the unwisdom of hindsight. In
excuse of that book it is probably true that, were we to meet a Homo erectus
face to face, it might well look to our eyes like an unfinished sculpture
in the making. But that is only because we are looking with human hindsight.
A living creature is always in the business of surviving in its own
environment. It is never unfinished -- or, in another sense, it is always
unfinished. So, presumably, are we.

The conceit of hindsight tempts us at other stages in our history. From
our human point of view, the emergence of our remote fish ancestors from
water to land was a momentous step, an evolutionary rite of passage. It
was undertaken in the Devonian Period by lobe-finned fish a bit like
modern lungfish. We look at fossils of the period with a pardonable
yearning to gaze upon our forebears, and are seduced by a knowledge of
what came later: drawn into seeing these Devonian fish as "half way" towards
becoming land animals; everything about them earnestly transitional,
bound into an epic quest to invade the land and initiate the next
big phase of evolution. That is not the way it was at the time. Those Devonian
fish had a living to earn. They were not on a mission to evolve,
not on a quest towards the distant future. An otherwise excellent book about
vertebrate evolution contains the following sentence about fish which
ventured out of the water on to the land at the end of the Devonian Period
and jumped the gap, so to speak, from one vertebrate class to another
to become the first amphibians . . .

The "gap" comes from hindsight. There was nothing resembling a gap at
the time, and the "classes" that we now recognise were no more separate,
in those days, than two species. As we shall see again, jumping gaps is not
what evolution does.

It makes no more sense (and no less) to aim our historical narrative
towards Homo sapiens than towards any other modern species -- Octopus
vulgaris, say, or Panthera leo or Sequoia sempervirens. A historically
minded swift, understandably proud of flight as self-evidently the premier
accomplishment of life, will regard swiftkind -- those spectacular
flying machines with their swept-back wings, who stay aloft for a year
at a time and even copulate in free flight -- as the acme of evolutionary
progress. To build on a fancy of Steven Pinker, if elephants could write
history they might portray tapirs, elephant shrews, elephant seals and
proboscis monkeys as tentative beginners along the main trunk road of
evolution, taking the first fumbling steps but each -- for some reason --
never quite making it: so near yet so far. Elephant astronomers might
wonder whether, on some other world, there exist alien life forms
that have crossed the nasal rubicon and taken the final leap to full
proboscitude.

We are not swifts nor elephants, we are people. As we wander in
imagination through some long-dead epoch, it is humanly natural to reserve
a special warmth and curiosity for whichever otherwise ordinary
species in that ancient landscape is our ancestor (it is an intriguingly
unfamiliar
thought that there is always one such species). It is hard to deny
our human temptation to see this one species as "on the main line" of
evolution, the others as supporting cast, walk-on parts, sidelined cameos.
Without succumbing to that error, there is one way to indulge a legitimate
human-centrism while respecting historical propriety. That way is
to do our history backwards, and it is the way of this book.

Backward chronology in search of ancestors really can sensibly aim
towards a single distant target. The distant target is the grand ancestor of
all life, and we can"t help converging upon it no matter where we start --
elephant or eagle, swift or salmonella, wellingtonia or woman. Backward
chronology and forward chronology are each good for different purposes.
Go backwards and, no matter where you start, you end up celebrating
the unity of life. Go forwards and you extol diversity. It works
on small timescales as well as large. The forward chronology of the
mammals, within their large but still limited timescale, is a story of
branching diversification, uncovering the richness of that group of hairy
warmbloods. Backward chronology, taking any modern mammal as our
starting point, will always converge upon the same unique ur-mammal:
shadowy, insectivorous, nocturnal contemporary of the dinosaurs. This
is a local convergence. A yet more local one converges on the most recent
ancestor of all rodents, who lived somewhere around the time the dinosaurs
went extinct. More local still is the backward convergence of all
apes (including humans) on their shared ancestor, who lived about 18
million years ago. On a larger scale, there is a comparable convergence to
be found if we work backwards from any vertebrate, an even larger
convergence
working backwards from any animal to the ancestor of all animals.
The largest convergence of all takes us from any modern creature
-- animal, plant, fungus or bacterium -- back to the universal progenitor
of all surviving organisms, probably resembling some kind of bacterium.
I used "convergence" in the last paragraph, but I really want to reserve
that word for a completely different meaning in forward chronology. So
for the present purpose I shall substitute "confluence" or, for reasons that
will make sense in a moment, "rendezvous". I could have used "coalescence",
except that, as we shall see, geneticists have already adopted it in a
more precise sense, similar to my "confluence" but concentrating on
genes rather than species. In a backward chronology, the ancestors of any
set of species must eventually meet at a particular geological moment.
Their point of rendezvous is the last common ancestor that they all
share, what I shall call their "Concestor":* the focal rodent or the focal
mammal or the focal vertebrate, say. The oldest concestor is the grand
ancestor of all surviving life.

We can be very sure there really is a single concestor of all surviving
life forms on this planet. The evidence is that all that have ever been examined
share (exactly in most cases, almost exactly in the rest) the same
genetic code; and the genetic code is too detailed, in arbitrary aspects of
its complexity, to have been invented twice. Although not every species
has been examined, we already have enough coverage to be pretty certain
that no surprises -- alas -- await us. If we now were to discover a life
form sufficiently alien to have a completely different genetic code, it
would be the most exciting biological discovery in my adult lifetime,
whether it lives on this planet or another. As things stand, it appears that
all known life forms can be traced to a single ancestor which lived more
than 3 billion years ago. If there were other, independent origins of life,
they have left no descendants that we have discovered. And if new ones
arose now they would swiftly be eaten, probably by bacteria.

The grand confluence of all surviving life is not the same thing as the
origin of life itself. This is because all surviving species presumably share
a concestor who lived after the origin of life: anything else would be an
unlikely coincidence, for it would suggest that the original life form im-

* I am grateful to Nicky Warren for suggesting this word.

mediately branched and more than one of its branches survive to this
day. Current textbook orthodoxy dates the oldest bacterial fossils at
about 3.5 billion years ago, so the origin of life must at least be earlier
than that. If we accept a recent disputation* of these apparently ancient
fossils, our dating of the origin of life might be a bit more recent. The
grand confluence -- the last common ancestor of all surviving creatures
-- could pre-date the oldest fossils (it didn"t fossilise) or it could have
lived a billion years later (all but one of the other lineages went extinct).
Given that all backward chronologies, no matter where they start,
culminate in the one grand confluence, we can legitimately indulge our
human preoccupation and concentrate upon the single line of our own
ancestors. Instead of treating evolution as aimed towards us, we choose
modern Homo sapiens as our arbitrary, but forgivably preferred, starting
point for a reverse chronology. We choose this route, out of all possible
routes to the past, because we are curious about our own great
grancestors. At the same time, although we need not follow them in detail,
we shall not forget that there are other historians, animals and plants
belonging to other species, who are independently walking backwards
from their separate starting points, on separate pilgrimages to visit their
own ancestors, including eventually the ones they share with us. If we retrace
our own ancestral steps, we shall inevitably meet these other pilgrims
and join forces with them in a definite order, the order in which
their lineages rendezvous with ours, the order of ever more inclusive
cousinship.

Pilgrimages? Join forces with pilgrims? Yes, why not? Pilgrimage is an
apt way to think about our journey to the past. This book will be cast in
the form of an epic pilgrimage from the present to the past. All roads
lead to the origin of life. But because we are human, the path we shall follow
will be that of our own ancestors. It will be a human pilgrimage to
discover human ancestors. As we go, we shall greet other pilgrims who
will join us in strict order, as we reach the common ancestors we share
with them.

The first fellow pilgrims we shall greet, some 5 million years ago, deep

* J.W. Schopf "s much-cited evidence for 3.5 billion-years-old bacteria has
been sharply criticised by my Oxford colleague Martin Brasier. Brasier may
be right about Schopf "s evidence, but new evidence, published when this
book was in proof, may reinstate 3.5 billion years as the date of the oldest
fossils. The Norwegian scientist Harald Furnes and his coworkers found tiny
holes in volcanic glass of that age in South Africa, which they believe were
etched by micro-organisms. These "burrows" contain carbon, which the
discoverers claim is of biological origin. No trace of the micro-organisms
themselves remains.

in Africa where Stanley memorably shook hands with Livingstone, are
the chimpanzees. The chimpanzee and bonobo pilgrims will already
have joined forces with each other "before" we greet them. And here we
have a little linguistic trickiness which I must face at the outset, before it
dogs us any further. I placed "before" in inverted commas because it could
confuse. I used it to mean before in the backwards sense -- "before, in the
course of the pilgrimage to the past." But that of course means after in the
chronological sense, the exact opposite meaning! My guess is that no
reader was confused in this particular case, but there will be other instances
where the reader"s patience may be tested. While writing this
book I tried the experiment of coining a new preposition, tailored to the
peculiar needs of a backward historian. But it didn"t fly. Instead, I shall
adopt the convention of "before" in inverted commas.When you see "before",
remember that it really means after! When you see before, it really
means before. And the same for "after" and after, mutatis mutandis.
The next pilgrims with whom we shall rendezvous as we push back
along our journey are gorillas, then orang utans (quite a lot deeper into
the past, and probably no longer in Africa). Next we shall greet gibbons,
then Old World monkeys, then New World monkeys, then various other
groups of mammals . . . and so on until eventually all the pilgrims of life
are marching together in one single backward quest for the origin of life
itself. As we push on back, there will come a time when it is no longer
meaningful to name the continent in which a rendezvous takes place: the
map of the world was so different, because of the remarkable phenomenon
of plate tectonics. And further back still, all rendezvous take place in
the sea.

It is a rather surprising fact that we human pilgrims pass only about
40 rendezvous points in all, before we hit the origin of life itself. At
each of the 40 steps we shall find one particular shared ancestor, the
Concestor, which will bear the same labelling number as the Rendezvous.
For example, Concestor 2, whom we meet at Rendezvous 2, is the most
recent common ancestor of gorillas on the one hand and {humans +
{chimpanzees + bonobos}} on the other. Concestor 3 is the most recent
common ancestor of orang utans and {{humans + {chimpanzees +
bonobos}} + gorillas}. Concestor 39 is the grand ancestor of all surviving
life forms. Concestor 0 is a special case, the most recent ancestor of
all surviving humans.

We shall be pilgrims, then, sharing fellowship ever more inclusively
with other pilgrim bands, which also have been swelling on their own
way to their rendezvous with us. After each meeting, we continue together
on the high road back to our shared Archaean goal, our "Canter-
bury". There are other literary allusions, of course, and I almost made
Bunyan my model and Pilgrim"s Regress my title. But it was to Chaucer"s
Canterbury Tales that I and my research assistant Yan Wong kept returning
in our discussions, and it seemed increasingly natural to think of
Chaucer throughout this book.

Unlike (most of) Chaucer"s pilgrims, mine do not all set out together,
although they do set off at the same time, the present. These other
pilgrims aim towards their ancient Canterbury from different starting
points, joining our human pilgrimage at various rendezvous along the
road. In this respect, my pilgrims are unlike those who gathered in London"s
Tabard Inn. Mine are more like the sinister canon and his understandably
disloyal yeoman, who joined Chaucer"s pilgrims at Boughtonunder-
Blee, five miles short of Canterbury. Following Chaucer"s lead,my
pilgrims, which are all the different species of living creature, will have
the opportunity to tell tales along the way to their Canterbury which is
the origin of life. It is these tales that form the main substance of this
book.

Dead men tell no tales, and extinct creatures such as trilobites are
deemed not to be pilgrims capable of telling them, but I shall make
exceptions
of two special classes. Animals such as the dodo, which survived
into historical times and whose DNA is still available to us, are treated as
honorary members of the modern fauna setting off on pilgrimage at the
same time as us, and joining us at some particular rendezvous. Since we
are responsible for their so recent extinction, it seems the least we can do.
The other honorary pilgrims, exceptions to the rule that dead men tell
no tales, really are men (or women). Since we human pilgrims are directly
seeking our own ancestors, fossils that might plausibly be considered
candidates for being our ancestors are deemed members of our human
pilgrimage and we shall hear tales from some of these "shadow
pilgrims", for example the Handyman, Homo habilis.

I decided it would be twee to let my animal and plant tale-tellers
speak in the first person singular, and I shall not do so. Save for occasional
asides and prefatory remarks, Chaucer"s pilgrims don"t either.
Many of Chaucer"s Tales have their own Prologue, and some have an
too, all written in Chaucer"s own voice as narrator of the pilgrimage.
I shall occasionally follow his example. As with Chaucer, an epilogue
may serve as a bridge from one tale to the next.

Before his Tales begin, Chaucer has a long General Prologue in which
he sets out his cast list: the professions and in some cases the names of
the pilgrims who are about to set off from the tavern. Instead, I shall introduce
new pilgrims as they join us. Chaucer"s jovial host offers to guide
the pilgrims, and encourages them to tell their tales to while away the
journey. In my role as host I shall use the General Prologue for some
preparatory remarks about methods and problems of reconstructing
evolutionary history, which must be faced and solved whether we do our
history backwards or forwards.

Then we shall embark on our backwards history itself. Although we
shall concentrate on our own ancestors, noting other creatures usually
only when they join us, we shall from time to time look up from our
road and remind ourselves that there are other pilgrims on their own
more or less independent routes to our ultimate destination. The numbered
rendezvous milestones, plus a few intermediate markers necessary
to consolidate the chronology, will provide the scaffolding for our journey.
Each will mark a new chapter, where we halt to take stock of our pilgrimage,
and maybe listen to a tale or two. On rare occasions, something
important happens in the world around us, and then our pilgrims may
pause briefly to reflect on it. But, for the most part, we shall mark our
progress to the dawn of life by the measure of those 40 natural milestones,
the trysts that enrich our pilgrimage.

Copyright © 2004 by Richard Dawkins. Reprinted by permission of Houghton
Mifflin Company.


Library of Congress subject headings for this publication:
Evolution (Biology) -- History.
Evolution (Biology) -- Philosophy.