Nobody knows the precise total of species that presently inhabit
the Earth, nor how many once existed but are now extinct. There could
quite easily be twenty million species alive today, and the number of
extinct species must run into the hundreds of millions, if not the
billions. Within this vast plenitude it is perhaps rather surprising
that there is only one, unique species that can understand a single
word of this book. This species, which is of course ourselves, is
uniquely privileged: not only can we understand something of our
origins, but we are the first animals ever to have looked at the
stars and seen anything more than distant pin-pricks of light.
Because, in some ways, we are utterly different from any other form
of life that has ever evolved, how do we know that our origins and
history are to be traced here on Earth rather than as extraterrestrial
immigrants? The reason is simple: our evolutionary pedigree is stamped
on every feature and permeates the entire fabric of our bodies. Some
aspects of our history are of comparative recency. For example, our
ability to walk upright (the bipedal stance) was achieved only about
four and a half million years (Ma) ago. The astonishing increase in our
brain size, even in comparison with the closely related apes, is yet
more recent. The basic structure of our arms and our legs, including
the characteristic five fingers and toes (technically the pentadactyl
limb), can be traced back over hundreds of millions of years. Indeed,
it is now possible to study fossils, including some collected from
Devonian rocks (about 370 Ma old) in east Greenland, that indicate how
the fins of aquatic fish were transformed into the limbs of the first
terrestrial vertebrates. Similarly, although our brains are unique in
their mental and spiritual faculties, the basic structure of the brain
is easily identifiable in primitive fish. This arrangement must have
evolved at least 500 Ma ago. But our evolutionary history is much more
deeply encoded than organs such as limbs and brains. In many ways our
basic biochemistry is little different from that of the bacteria.
These steps in evolution were achieved thousands of millions of years
ago. Not only do we and bacteria both use DNA for replication, but
special proteins (the histones) that surround the strand of DNA and
assist with keeping it stable and in the correct configuration are
very similar in their sequence of building blocks (the amino acids)
in all life. This is simply because they play a fundamental role in
maintaining the proper function of the DNA; most alterations are
automatically fatal.
It is, however, self-evident, even if the histone proteins are
almost invariant in their structure, that life itself has not
remained at the level of bacteria. The world is full, not only of
bacteria, but also of animals as different as cranes, whales,
oysters, and sharks, not to mention the plants, fungi, and
single-celled organisms such as Amoeba. This book is not directly
concerned with the origins of any of these creatures, or indeed
ourselves. Rather it is an exploration of how a single unit of
rock, from the west of Canada and known as the Burgess Shale, has
placed the history of life, and so by implication Man's place in
the scheme of evolution, in a new set of contexts.
What then is this Burgess Shale and why is it regarded as so
important? How it was discovered, who worked on it, what scientific
mistakes they inevitably made, how much remains to be learnt, and
whether the whole concept of evolution in the Darwinian framework
now needs to be radically reconsidered will all be considered in
the rest of this book. The Burgess Shale is a thin unit of rock.
The outcrop itself, in a small quarry on the side of a hill, is
rather drab and unremarkable, but any palaeontologist would want
to work there for two reasons. One is seemingly trivial: even if
the quarry looks very ordinary, the Burgess Shale occurs in some
of the most beautiful scenery in the world, in the Main Ranges of
the Canadian Rocky Mountains. Looking from the quarry, as far as
the eye can see, there are snow-capped mountains, glaciers,
turquoise-coloured lakes, and forests set in wilderness. If one
has to collect fossils, one might as well collect them here! The
second reason is that the Burgess Shale is no ordinary fossil
deposit. Here, by as yet largely unknown mechanisms, the processes
of rotting and decay have been largely held in abeyance so that
the true richness of ancient life is revealed: not only are there
animals such as trilobites and molluscs with tough, durable
skeletons, but completely soft-bodied animals are also preserved.
These remarkable fossils reveal not only their outlines but
sometimes even internal organs such as the intestine or muscles.
The Burgess Shale is not unique, but for those who study
evolution and fossils it has become something of an icon. It
provides a reference point and a benchmark, a point of common
discussion and an issue of universal scientific interest. Just
as Darwin's finches from the Galapagos Island exemplify the
recognition of the central role of adaptation, or the laboratory
fly Drosophila stands as a symbol for the profound successes of
molecular biology, so the Burgess Shale is becoming the icon for
those who study the history of life. But before we begin to
understand what the riches of the Burgess Shale mean, both to
evolution and the scientific method, it is essential to place
it in a wider context. By obtaining a sense of its place in the
unfolding drama of life, set in an ecological theatre, so we
can understand why it has become one of the leading players.
Evolution: why no consensus?
All science is embedded in a framework, which provides the
points of reference and a necessary stability to our enterprise.
Not surprisingly, many aspects of the framework remain little
changed for decades, and on a day-to-day basis are accepted and
usually remain unchallenged. For biology it has been famously
observed that nothing makes sense unless considered in the
context of evolution. The fact of organic evolution in itself
is not in dispute. This is because in essence the Darwinian
formulation of descent through time and co-occurring modification
of the organisms, usually registered in the fossil record by
anatomical changes, seems to be unanswerably correct. Once there
were only bacteria; now they share the planet with millions of
other types of life. Separate and special creation of each and
every species is a logical alternative, and in itself need not
be beyond reason. Nevertheless, the study of comparative anatomy,
behaviour, molecular biology, and the fossil record give no
support to any such model of recurrent creation.
So if we accept a tree of life, arising from a single ancestor
approximately four thousand million years ago, why does the
apparently simple fact of organic evolution excite continuing
debate and disagreement? What is it that is in dispute? At heart
there are two areas of contention: those of mechanism and those
of implication. The first is a scientific problem, the second is
metaphysical. Our immediate concern here is with the aspects of
evolutionary theory (as presently portrayed) that are relevant
to the Burgess Shale. As with most areas of science, the argument
proceeds by reference to examples. The story of the Burgess Shale
therefore epitomizes many aspects of the debate on evolution, but
this extraordinary fauna is nevertheless no more than a convenient
vehicle that embodies the wider principles that are at stake.
A recurrent difficulty in discussions on organic evolution is
that schools of thought are too often polarized, although this is
understandable because of the need to solve tractable problems
that need to be stated in high circumscribed language.
Nevertheless, in all the debates and disagreement, it seems rather
extraordinary that for the most part it is almost forgotten that
evolution is a historical process. In part it is accessible from
the fossil record, and the analogies with the study of human
history are clear. For example, if I wish to know more about the
history of a college in Cambridge I can spend a rewarding time
in the archives, aware that not all documents are decipherable
and some may have been lost by fire, flood, or worm. Much can
also be learnt, however, from simply studying the present order,
be it of the buildings or the nature of its society. Here, too,
there will be a clear historical stamp. It is all the more
remarkable that the pitfalls and fallacies that the well-trained
historian teaches others to avoid do not seem to be utilized by
those investigating the parallels in the history of life. In a
society stricken by post-Saussurean relativism it is also too
often forgotten that history had a unique course, and that in
principle it is knowable.
What then of evolutionary mechanism? In brief, there seem to
be three main problems to consider. It is widely, although not
universally, agreed that central to the evolutionary process is
the splitting of lineages, with at least one of the descendant
forms differing materially from the ancestral type. Most
biologists identify this process as one of speciation, the
formation of new species. In classical biology this aspect of
evolution has been construed in terms of mechanisms that promote
the isolation of groups of individuals (populations) and thereby,
at some subsequent stage, an inability to interbreed or at least
produce fertile offspring. The frequency of hybridization, as
well as the possibility for the transfer of genetic material
between species, perhaps by the agency of bacteria, demonstrate
that species need not be watertight entities, at least
genetically. Forms transitional between species can be observed
today, and can be inferred to have existed in the past.
Nevertheless, the net result is very far from a seamless
tapestry of form that would allow an investigator to read the
Tree of Life simply by finding the intermediates—living and
extinct—that in principle connect all species. On the
contrary, biologists are much more impressed by the discreteness
of organic form, and the general absence of intermediates.
Here, therefore, lies an important area of tension in the
study of evolution. On the one hand the diversity of life can be
read from an essentialist point of view, one whose vocabulary
will include words such as body plan (or Bauplan) and archetype.
In their more far-flung moments of comparison, proponents will
take an effectively Platonic view that organic form reflects
some sort of universal order, akin to the ideal solids of
Platonic metaphysics. In this essentialist view the implication
is that organic diversity is imposed, rather than evolved. It
will also be clear that the essentialist views could be
compatible with those that seek evidence for special creation in
organic form. In marked contrast is an alternative viewpoint of
evolutionary processes that might be linked to the famous
Heraclitean flux of continuous change. In one sense this must be
uncontroversial because, barring appeals to hopeful monsters
testing their saltatory abilities, the facts of evolution point
to building up on previously available organic designs in a
gradualistic manner. Whatever is in dispute about evolution, it
is not the derivation of one type from another. But if we accept
the reality of transitions do we not have to explain why large
sections of potential morphospace remain unoccupied? If this is
the correct analysis, as indeed it appears to be, then a more
profound problem emerges as to whether such vacancies reflect
lack of chance or opportunity, or whether (as seems more
plausible to most Darwinian biologists) some zones of organic
form (or morphospace) are effectively impossible to colonize
because any organism occupying them would be seriously maladapted.
In an ideal case such regions of morphospace are described
mathematically. One such example is given in Chapter 8, where an
example is taken from the extinct trilobites. In many other cases
a precise mathematical description that defines the morphospace
occupied by a group of organisms remains a very challenging
prospect, but headway has been made. One of the best-known
examples concerns the growth and hence geometry of the shells
secreted by the molluscs, a group familiar from animals such as
the garden snail and edible mussel. Although not immediately
apparent, the geometry of nearly all mollusc shells can be
reduced to several simple equations that together describe
their various shapes. What this means is that any point in
mollusc shell morphospace can be defined according to a given
solution of these equations. Not surprisingly, when applied to
the real world such an analysis shows some regions of morphospace
to be thickly populated by shell types that are relatively
familiar. Other zones, however, are more or less empty. In these
latter cases, the equations can be readily used to visualize
the hypothetical shell shape we would find if this region of
morphospace was occupied, but somehow they look `wrong'. Such
regions of morphospace housing these aberrant shells need not be
entirely vacant, but the most likely explanation is that such forms
are (or were) at a serious selective disadvantage for reasons
such as mechanical weakness or vulnerability to predation.
To return to the specifics of organic evolution. It is generally
accepted that the origins of divergence of form are coincident with
the processes of speciation itself. Although it may be a mistake to
think of speciation as a single process, the end results of these
processes seem to be much the same. Let us accept then, if only for
the sake of the argument, that not only are species discrete
entities, but that they arose from pre-existing forms from which
they differed in some material aspect. The central question is: are
the processes of speciation in themselves sufficient to explain the
pattern of life that we see today or at any time in the geological
past? For nearly all biologists the fact of speciation is not in
dispute, but its role in driving evolution is much more contentious.
For those who do not accept speciation as the main motor of organic
diversity, there are broadly two approaches. There are those who
look to the molecular dynamics of the genome, as against those who
seek some wider view that transcends the species. Thus, according
to a number of molecular biologists the crux of the investigation
needs to move to the genome and the reorganization and reshuffling
of pieces of DNA, the molecular units of heredity. It is certainly
realized that the genome is much more dynamic than was once thought.
For example, there are large variations in the amount of DNA in
different species, and it is still far from clear why some organisms
have such huge excesses in DNA. There is little connection to
complexity: humans for example have relatively modest amounts of
DNA in each cell, but to dismiss--as some have done--the apparently
excess DNA as `junk' may be too simplistic. Not only can the amount
of DNA in the chromosomes be dramatically increased, but in addition
genes can be shuffled, moved around, or duplicated. There is also
evidence for transfer of genetic material within the cell, notably
moving DNA from the organelles known as mitochondria (which house
their own separate circular chromosome) to the main storehouse of
DNA in the chromosomes housed in the nucleus. In itself this
activity need not be under the scrutiny of natural selection,
even if the end result, the expressed phenotype, is moulded and
constrained by the classical Darwinian principles of variation
followed by selective culling. At the other end of the spectrum
are those who argue that it is the evolutionary processes
operating above the level of species that are unjustly neglected.
There has been particular interest in a mechanism referred to as
species selection, which in outline states that a propensity to
speciation, in itself unrelated to the operation of natural
selection, will favour one clade, that is, a set of species sharing
a common ancestor, over another clade. While the principle of
species selection appears to be logical, there are to date very few
case-examples to suggest that it is of particular significance.
There are other aspects to organic evolution that are certainly
not ignored, but perhaps still receive insufficient emphasis. One
is the influence of the environment. This would seem to be
unremarkable, until it is realized that much of current thinking
seems to be firmly embedded in a uniformitarian framework, that is,
it assumes that present-day conditions are a sufficient guide to
understanding past worlds. In some ways this must be true: the sun
shines, water is wet, and things fall out of trees. But in other
ways the Earth has clearly changed dramatically. It appears that
in the past 600 million years the composition of the atmosphere,
notably in terms of oxygen and carbon dioxide, has changed
significantly. Times of elevated oxygen levels, for example,
coincide with gigantism and the development of flight in some
animals. There is a suspicion that there is a causal connection.
Here is another example. Further back in time the Moon was probably
much closer to the Earth. Because of the inverse square law of
gravitational attraction, the proximity of the Moon would then have
generated immense tides. What effect did these have on primitive
life? Could this explain, in part, the sluggishness of organic
evolution at this time? This might not be the only environmental
constraint. Some workers have suggested that early in the history
of the Earth surface temperatures were significantly elevated, and
this too could have exerted a powerful brake on organic
diversification.
Nor need the controls on evolution be exerted by environment
alone. Barring sudden catastrophes, such as the arrival of a giant
meteorite, most environmental factors will change at an imperceptible
rate when compared with the generation times of living populations.
But evolution proceeds not only in a real physical world, but in a
biological arena. It would be simplistic to imagine that species are
`locked in' to an ecological framework, but the communities and
biomes which they occupy must exert some degree of constraint.
It will be clear by now that although the Darwinian framework
provides the logical underpinning to explain organic evolution, the
actual pattern of life we observe may require a more complex set of
explanations. Those who believe that their viewpoint is being
neglected may be strident in their claims. Perhaps one reason for
the continuing debate is that as a whole the various mechanisms
proposed are each eminently reasonable. It is the problem of
deciding if one such mechanism deserves primacy of effect, or whether
the question `Why do organisms evolve?' is unanswerable until one
specifies the mechanism and the level at which it may operate. In
such a large and complex field, the main strands of debate, and
sometimes enquiry, are accordingly difficult to disentangle, not
least because among some of the main proponents there are often
broad areas of agreement. Indeed, some generate an aura of apparent
accommodation by stressing their plurality of approach. On closer
examination, however, this sometimes transpires to be skin-deep.
Moreover, those with ideological training know that the tactics of
persuasion may be assisted by the invention of key phrases that
demonize the opposition.
Who then are the main proponents? Because of his earlier
discussion of the Burgess Shale fauna, it is essential to review
the contributions of Stephen Gould. But before doing so it is
necessary to introduce briefly those who would regard their view
of the evolutionary process as more or less antithetical to that
of Gould. This latter group can be labelled, I think fairly, as
hard Darwinists. One spokesman, Daniel Dennett, has elevated the
Darwinian method to what is effectively a universal principle.
The acid test of such a claim is whether such a formula can explain
what are presently regarded as the most fundamental and least
tractable of problems, notably those of cosmology and the early
history of the Universe and the onset of consciousness. For many
this is taking the principle too far, and it is certainly the
case that the entire philosophy is strongly materialist. In terms
of organic evolution nowhere is this more evident than in the
vigorous advocacy of Richard Dawkins. In a series of polemical,
but carefully argued and vividly expressed books, Dawkins has
unremittingly pursued the consequences--as he sees them--of the
Darwinian world picture. Although set in an adaptationist
landscape, a rolling and sometimes mountainous terrane that
encompasses not only form and function but also behaviour, his
fundamental point of reference is the primacy of the gene. In
this way, Dawkins takes a highly reductionist approach. Not
surprisingly, however clear the articulation, this programme
has generated controversy and unease because of a sense in which
the richness and diversity of evolution are being forced into an
atomistic mould. Dawkins would probably reply that he is only
seeking the underpinnings of the evolutionary process, upon
which all else depends.
It is certainly the case that recent research into the
developmental processes in animals has been little short of
spectacular. At first sight these results seem to be consistent
with the primacy of the gene. In a number of instances it is
clear that a specific gene is associated with the expression of
a complex anatomical feature. One of the best-known examples
involves a so-called master-control gene which plays a key role
in the formation of eyes. In a classic but disturbing experiment,
the application of this gene to the fruit-fly led to an ectopic
expression, that is, to eyes growing on various parts of the body.
But this and similar genes hold further surprises that suggest
the story to be more complicated. First, it transpires that the
same gene (Pax-6 and its homologue eyeless) is employed not only
in flies and other insects to build their characteristic compound
eyes, but also in vertebrates. The eyes with which you read this
page result in one sense from the activity of the same gene. Yet,
despite the fact that both are light-receiving organs, there are
profound differences between the eyes of fly and Man. On further
reflection this need not surprise us. Most probably the Pax-6
gene is very ancient. It almost certainly predates the animal,
presumably some sort of worm, that about 600 million years ago
represented the common ancestor of flies and humans. Indeed
Pax-6 may predate the earliest animals. This is because its
function is to construct a light-sensitive unit, and such
structures are well known in a number of the more primitive
single-celled organisms whose origins almost certainly predate
the animals. Equally important the recognition of Pax-6 in
arthropods (flies) and vertebrates (humans) is good evidence
that they are indeed related, but it tells us nothing about
the manifest differences between the eyes with which we see
the fly, and the eyes of the fly which observe us as we advance
with rolled newspaper in hand.
It is in this manner that Dawkins's world view is not so much
wrong, as simply seriously incomplete. While few doubt that the
development of form is underwritten by the genes, at the moment
we have almost no idea how form actually emerges from the genetic
code. In his enjoyable book The shape of life the American
evolutionary biologist Rudy Raff is bald in his assessment: `The
central problem is finding the mechanisms that connect genes and
developmental processes to morphological evolution' (p. 430). One
puzzling aspect, for example, is that species with very similar
adult forms may reach this final stage via markedly different
developmental pathways. These so-called trajectories may in
themselves have adaptive significance, and no doubt different
sets of genes swing into action at different times. In addition,
seemingly major contrasts in anatomical arrangement may well
depend on trivial genetic differences. Until, however, we learn
what these are, we shall remain uninformed about the actual
mechanisms whereby the shape of life is moulded. It is certainly
difficult to see how the severely reductionist approach of
Dawkins will continue to provide the most satisfactory strategy.
Indeed, what has quite unexpectedly emerged is how seemingly
very different organisms have in common fundamentally the same
genetic information. Here is perhaps the central paradox of genes
and evolution: vast contrasts in morphology and behaviour need
have no corresponding differences in the genetic code.
Perhaps a suitable analogy to explain the short-falls of
Dawkins's account of evolution is to think of an oil painting. In
this analogy Dawkins has explained the nature and range of pigments;
how the extraordinary azure colour was obtained, what effect cobalt
has, and so on. But the description is quite unable to account for
the picture itself. This view of evolution is incomplete and
therefore fails in its side-stepping of how information (the genetic
code) gives rise to phenotype, and by what mechanisms. Organisms are
more than the sum of their parts, and we may also note in passing
that the world depicted by Dawkins has lost all sense of
transcendence.
In such a multifarious subject as evolution, it is certainly
possible to identify camps (and outposts), but it is less easy to
arrange them into a linear spectrum, let alone a simple polarity.
Yet, if there is some sort of antithesis to Dawkins's portrayal of
evolution, it is a yet stranger world inhabited by Stephen J. Gould,
who rivals Dawkins as a popularizer of evolutionary biology. At first
sight Gould's construction is much richer, especially in its appeals
to a plurality of mechanisms and forces. But it is also a less
constant world, or at least one where emphases and priorities shift.
The world picture offered by Dawkins, as I have suggested above, is
not so much wrong as simply too narrow and one-dimensional. The one
presented by Gould is much more difficult to encompass, but despite
its apparent vitality, I would argue that it is much more deeply
flawed. Because the faunas of the Cambrian, and especially the
Burgess Shale, have taken a key role in some of Gould's more recent
perorations, notably in the book
Wonderful life, it is necessary to take
into account the general background of his view of life, and so its
evolution.
To start with, Gould does not attempt to deny the importance of
the Darwinian explanation. And indeed why should he? Some of the most
cogent and readable explanations of these evolutionary principles are
compelling and fascinating, especially those concerning the manner in
which complex structures are `jury-rigged' from pre-existing
structures in an apparently contrived way, the nature of which clearly
reveals the deep historical imprint of evolutionary activity. But
Gould has also not ceased to champion the notion that the Darwinian
explanation is in some way incomplete. It is hardly surprising that
he has found himself at loggerheads with Dawkins. Again and again Gould
has been seen to charge into battle, sometimes hardly visible in the
struggling mass. Strangely immune to seemingly lethal lunges he finally
re-emerges. Eventually the dust and confusion die down. Gould announces
to the awestruck onlookers that our present understanding of
evolutionary processes is dangerously deficient and the theory is
perhaps in its death throes. We look beyond the exponent of doom, and
there standing in the sunlight is the edifice of evolutionary theory,
little changed. One source of unease in Gould's writing is what appears
to some people as the fine line between argument and rhetoric. Thus, a
favourite rallying cry of his was to label the neo-Darwinian programme,
largely built on the population genetics of Morgan and Dobhansky and
the mathematics of Fisher, as hopelessly sclerotic: what Gould famously
labelled as `the hardening of the synthesis'. This was a master stroke
of invective, and is perhaps reminiscent of the political tactic of
picking a resonant phrase to box in and demonize one's opponents. But
is it a fair comment? There was only a `hardening' inasmuch as what
the neo-Darwinian school set out to do was immensely successful, and
was pursued with vigour. Did it stifle research? If neo-Darwinians
turned their collective back on a much-vaunted plurality of
alternative evolutionary mechanisms, were they ultimately so unwise?
It is significant that the recent dramatic advances in developmental
biology can be directly traced to the painstaking work of these
earlier neo-Darwinian geneticists. Not only that, but the repeated
invitations to reinstate such individuals as Richard Goldschmidt and
Otto Schindewolf from being isolated voices in the wilderness to
occupy a favoured place in the pantheon of evolutionary biology
have quite simply failed. That both these individuals made important
contributions is not in dispute, but at the time were they ever a
serious threat to our understanding of the evolutionary process?
Although less commented upon than Goldschmidt, whose work on
butterflies has been overshadowed by his celebrated leap into
macroevolutionary thought by the agency of his much-discussed
`hopeful monsters', Schindewolf is also an interesting case
history. Embedded in Spenglerian cyclicity, whereby groups of
organisms contained the seeds of their disaster and from high
triumph descended into decadence and rottenness, his scientific
influence in Germany was enormous, and baneful. A rather sinister
combination of autodictat and adherence to a flawed philosophy
led German palaeontology into a cul-de-sac of sterile
macroevolutionary speculation and an anti-Darwinian attitude that
persisted for many years after the overthrow of the Nazis.
Such is the complexity of evolutionary discussion that it would
not be fair to dismiss what are now generally thought of as hopeless
cases without a fair hearing. That evolution is rich in unsolved
problems is not in dispute. It is certainly true that Gould's
enthusiastic promulgation of various alternatives to evolutionary
orthodoxies has made the guardians of neo-Darwinism look more
carefully at their received truths. These alternatives have
generated healthy debate. There needs, however, to come a time
not only for summation and the taking of stock, but also to
enquire whether other problems of evolution remain neglected.
Take the case of adaptation, a key element in the Darwinian
framework. That it exists is not in dispute, but is it crucial to
our wider understanding of evolution? After all, if combinations
of characters and traits can `slip past' the scrutiny of natural
selection, then perhaps the architecture will reveal unexpected
riches. And it was by a characteristically inventive, but as we
can now see flawed, metaphor that Gould started a debate on the
importance of adaptation that now looks to be increasingly misplaced.
He fired the first shot in his paper (with R.C. Lewontin) on the
spandrels of the Doges' chapel in Venice, the famous San Marco.
(A spandrel can be defined in more than one way, but here it can be
regarded as the roughly triangular space between the shoulders of
two adjacent arches and the horizontal line immediately above their
heads.) The argument that Gould and Lewontin put forward was that
just as these architectural features are incidental to the design
of the building, so organisms also house their own `spandrels',
which are similarly without adaptational significance. A supposed
architectural by-product was taken as the introduction to a
polemic on the dangers of viewing the world through adaptationist
spectacles. But in fact Gould and Lewontin's analysis is
fundamentally flawed. Spandrels are very far from being incidental
by-products of construction and are central to design and safety.
It may be no accident that the almost universal human admiration
of adaptation in the organic world is in some ways echoed in such
buildings as San Marco. The spandrels, or more properly pendentives,
house some of the glowing and mysterious Byzantine-inspired mosaics
that draw the observer towards a deeper contemplation of Christian
faith. Moreover, is not much of our disenchantment with the
barbarity of much recent architecture due to this banishment of
the numinous?
The case of the spandrels is one of the better known of Gould's
evolutionary perspectives, and is perhaps overshadowed only by the
hypothesis of punctuated equilibria. Nevertheless, despite some
shifts in emphasis, the underlying ideological agenda of Gould has
always been fairly clear. Even where there has been a shift in
thinking, it might be argued that in general the discussions were
reflecting a particular world-view that at the least was sympathetic
to the greatest of twentieth-century pseudo-religions, Marxism. Thus
at one stage an influential group of American biologists was
interested in exploring a so-called nomothetic view of evolution.
This was an attempt, perhaps futile, to seek general laws of
evolution, which if discovered might allow the practitioners to
claim that evolutionary biology was a `hard' science, comparable in
some sense to chemistry and physics. As is well known, the Marxist
agenda has long sought `laws' of history, principally linked to
certain inevitable outcomes that strangely favoured those fortunate
enough to have formulated the `laws' in the first place. There is,
of course, no suggestion that the hegemony of an ideology is to be
transferred to the inevitability of a certain view of biology. My
point rather is that the nomothetic investigation of historical
sciences may reveal some interesting parallels. In any event, so
far as evolutionary biology is concerned this programme has been
effectively abandoned; apart, that is, from a small group of
anti-Darwinians who have pursued the enterprise in the rather
different direction of explaining organismal form by various
underlying `forces'. In the meantime, of course, there has been a
spectacular growth of interest in the operation of mathematical
systems of non-linear dynamics, popularly referred to as chaos
theory.
In more recent years Gould has promulgated a rather different set
of notions that emphasize the role of the contingent in evolution.
At first sight it is quite difficult to decide whether any of this
needs to be taken seriously--until, that is, the underlying message
is decoded. It is indeed somewhat surprising that the operation of
contingency needs any comment at all. After all, if St Thomas Aquinas
had no difficulty in reconciling the order of a Universe stemming
from the Act of a Creator, part of which entailed a contingent world,
then we might wonder how those involved with the more mundane role of
explaining evolution could sense that contingent events had been an
overlooked part of the puzzle. If thorough-going theists, who
traditionally have been supposed to be hostile to the scientific
theories of evolution, are content to accept contingency, then one
might presume that its operation in the history of life would pass
unremarked. And so it might, until it was seized upon by Gould as a
point worth serious discussion. In brief his argument, largely using
the Burgess Shale faunas, was that the range of variation in the
Cambrian was so huge and the end results in terms of the diversity of
today's world so restricted that the history could be regarded as one
colossal lottery. Forget the big battalions, inspired leadership, the
idiosyncrasy of genius, the professionalism of the academies, or any
of the other factors that are routinely used to explain the twists
and turns of human history, and by analogy the history of life:
quite possibly they are relevant to the human condition, but no such
correspondence existed in the natural world. Here chance reigned
supreme, with the corollary that what to us constitutes the utterly
familiar was in principle no more inevitable than a million other
outcomes, ones in which humans would assuredly play no part. So much
for the flights of rhetoric. Here, nevertheless, we are with one
state of affairs--the world around us. How could we ever show that
a plenitude of alternatives was equally likely, with the important
corollary that nothing like us humans would be there in this
imaginary world, either to ponder or to celebrate?
I presume that the best test of this supposition would be the
discovery of a distant planet, sufficiently Earth-like to support
some sort of animal life. In Chapter 9 I note that the likelihood
of extraterrestrial life itself, let alone anything remotely like
a human, may be much more remote than is popularly supposed. But
in the immediate terms of discussing the outcomes of alternative
histories, quite possibly with only marginal differences in the
starting conditions, the question of whether there is or is not
extraterrestrial life may not be too material to the argument. In
one sense the experiment of alien life has been carried out, but
here on Earth. Thus, although there is of course an evolutionary
continuity in the history of life, it is also the case that not
only are nearly all the species that have ever lived now extinct,
but entire ecosystems have also vanished. In these past worlds there
was much that was novel and has no counterpart today. But it is also
true that much is familiar. This is not so much to do with evolutionary
continuity, but the phenomenon known as convergence. Any textbook of
evolution that fails to mention convergence would be guilty of serious
dereliction. Yet despite the classic examples, which vary from the
anecdotal to the closely argued, the study of convergence and the
constraints of form, have, I believe, never been the subject of a
single synthesis. There are several reasons for this. One is its
simple ubiquity: convergence is taken for granted. Another is the
problem of formulating a precise metric of convergence. Famously,
the marine reptiles known as ichthyosaurs are remarkably similar to
the living dolphins; but are the convergences only superficial or
of deep significance? Convergence is seldom precise. In addition, to
identify convergence one must know the evolutionary tree that depicts
both the interrelationships and ancestral conditions. But this can
only be done on the basis of similarities of organization, be they
anatomical, behavioural, or molecular. Thereby lies the risk of
becoming trapped in a circular argument: are organisms similar
because they have converged or because they are descendants of a
common ancestor? In terms of specifics this remains a very serious
problem, but in terms of generalities the problem evaporates because
no matter what evolutionary tree is chosen, convergent features
almost invariably emerge. The reason for discussing convergence here
is that its recognition effectively undermines the main plank of
Gould's argument on the role of contingent processes in shaping the
tree of life and thereby determining the outcome at any one time.
Put simply, contingency is inevitable, but unremarkable. It need
not provoke discussion, because it matters not. There are not an
unlimited number of ways of doing something. For all its
exuberance, the forms of life are restricted and channelled.
For the great majority of biologists such a conclusion will hardly
be surprising. The agenda, however, once again is ideological, because
the discussions on contingency versus constraint seem to be more to
provide the background and focus of a very specific problem, that is
the rise of human intelligence. Gould's view is unequivocal. The
likelihood of Man evolving on any other planet is extraordinarily
unlikely. To paraphrase: if the history of evolution were to be
repeated, the world would teem with myriad forms of life (note that
the contingent likelihood of the origin of life itself goes through on
the nod), but certainly no humans. As stated, this seems to be entirely
unremarkable, although again it presupposes that the constraints are
weak. It is not, however, the point. What we are interested in is not
the origin, destiny, or fate of a particular lineage, but the
likelihood of the emergence of a particular property, say consciousness.
Here the reality of convergence suggests that the tape of life, to use
Gould's metaphor, can be run as many times as we like and in principle
intelligence will surely emerge. On our planet we see it in molluscs
(octopus) and mammals (Man). It might still be objected that the
properties expressed in Man have a uniqueness without precise parallel.
This may be a distortion of the time in which we fortuitously find
ourselves; what was rare in the last four thousand million years of
evolutionary history might be common in the next four thousand million
years. Weak support for this argument might come from the most closely
related species to us, the Neandertals. Perhaps independently they
developed some sort of sense of an afterlife, at least to judge from
their practice of deliberate burial. Materialists will scoff at this
as a shared delusion, but there are metaphysical alternatives that
are perhaps more fruitful.
But Gould's arguments on the quirkiness of human intelligence
are not only presented as part of an evolutionary argument, but also
I believe to buttress an ideological viewpoint. In brief, his
assessment of Man as an evolutionary accident is to lead us into a
libertarian attitude whereby, by virtue of a cosmic accident, we,
and we alone, have no choice but to take responsibility for our own
destiny and mould it to our desire. At the very least, the activities
of the last century as one of unrestricted political experimentation
should give us pause for thought. The implication of an evolutionary
process transcending the scientific evidence does indeed provide a
metaphysic, albeit one that is etiolated and impoverished, but it
should be decisively rejected. We do indeed have a choice, and we
can exercise our free will. We might be a product of the biosphere,
but it is one with which we are charged to exercise stewardship. We
might do better to accept our intelligence as a gift, and it may be
a mistake to imagine that we shall not be called to account.
As I noted above, we muddy the waters of the debate if we fail
to acknowledge that the processes of evolution have metaphysical
implications for us. This is because uniquely there is inherent in
our human situation the possibility of transcendence. The fact that
we arrived here via an immensely long string of species that
originated in something like Pikaia rather than some other
crepuscular blob is a wonderful scientific story, but it is hardly
material to our present condition.
[ Simon Conway-Morris, 
