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“Was the first craniate on the road
to cognition?”
Evolution and Cognition 2003; 9(2):142-156.
Fredric J. Heeren (Page 4)
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Something Missing
Some paleontologists see such strong
trends in the fossil record that they don’t believe
contingent events can overcome them. Jun-Yuan CHEN believes
that there must be other forces driving evolution toward
intelligence besides natural selection and mutations. If
evolution were restricted to these two forces, he says, then
all life would still be microbial. “Bacteria are very
successful”, pointed out CHEN. “They have a great
capacity to adapt to environmental changes” (personal
communication). And he noted that bacteria have flourished
better than other life forms that have come and gone over
billions of years without complexity or intelligence. Complex
life, CHEN said, is less capable of making adaptations, so that
“complex, highly evolved life, like the human, has no
reason to appear. So why should these chance mutations plan
such complex types of animals?” (Ibid). What’s
missing from neo-DARWINISM?
Wallace ARTHUR pictures neo-DARWINIAN
theory as a grand edifice with foundations and walls that are
composed of interdependent disciplines, so that “if one
part turns out to be wrong, the whole structure may eventually
collapse” (ARTHUR 1997, p285). Until the developmental
component has made its contribution, he says, “There is
not just a brick or two missing, but rather a whole section of
the building” (Ibid).
Physicist Paul DAVIES suspects that
biologists have concluded too rashly that they understand
life’s origin and evolution, and that “we are
missing something very fundamental about the whole
business” (DAVIES 1999, p17). Cosmologists routinely use
the term “anthropic principle” to describe the many
preconditions for complex life met by severely constricted
universal constants (BARROW/TIPLER 1986; BARROW 2002; GREENE
1999). These include the apparent “fine-tuning” of
the universe’s expansion rate (sometimes calculated to be
“tuned” to one part in 1060 at one second after the
big bang, as a precondition for life) (HAWKING 1988,
pp121–122; KRAUSS 1998) and the precise strengths of
nature’s four fundamental forces (e.g., the strength of
the electromagnetic force appears to be tuned relative to the
gravitational force to at least one part in 1036, as a
precondition for the existence of stable stars) (BARROW/ TIPLER
1986, p219; DAVIES 1983, p188; REES 1999, p2). DAVIES has long
wondered if biologists would see the constraints and the
bio-friendly pattern too.
CONWAY MORRIS sees something like it:
“Consider, for example, the sponges”, he writes,
“which by general consent are the most primitive living
metazoans. Nevertheless, their biochemistry includes elements
that seem to foreshadow the immune system of vertebrates”
(CONWAY MORRIS 2000; SCHÄCKE et al. 1994). Though sponges do
not have nerve cells, they already have neuronal-like
receptors, so that they “seem to be almost ‘animals
in waiting’” (CONWAY MORRIS 2000). CONWAY MORRIS
believes that caution is in order and that such findings can be
carried too far, producing a distorted view; yet he continues
listing examples of what appear as preadaptations, such as the
nervous system of amphioxus revealing “a vertebrate in
waiting” (Ibid).
Similarly, recent genetic studies of
hemichordates, which have no brains, show that these most
plausible models for proximate ancestors to chordates already
contain the genes that express the brain and spinal cord in
vertebrates (LACALLI 2003). Hemichordate genes that are
responsible for patterning the body along its front-to-back
axis were found expressed in the surface tissue in a nearly
identical arrangement to those that express themselves in
vertebrate brains and spinal chords (LOWE et al. 2003). LOWE et
al. favor the idea that a complex genetic map was in place long
before the complex morphology.
The bottom line, according to CHEN, is
that the standard mechanisms of neo-DARWINISM offer no basis
for a “ladder of progress”. So far, a
noncontroversial view. But if his “top-down”
alternative gains acceptance, it would create a paradigm shift
in biology. His replacement of competition with harmony and
top-down evolution could be taken to suggest the first rungs in
such a guiding ladder. CHEN’s discovery of Haikouella shows
that the last really big turn in the pathway to humanity did
not occur at the end of the evolutionary process, but at the
beginning. Does this mean that the “goal” of
humanity was set from the beginning of metazoan life? Few other
participants at the Kunming conference were willing to say
anything like that. But some did, including New Zealand
geneticist Michael DENTON.
Arguing from the fact that almost no new
phyla evolved after the Cambrian explosion, DENTON said:
“The body plans of the Cambrian are probably built into
nature from the beginning” (DENTON 1999). DENTON is part
of a team that recently revealed how, at its base, life follows
“laws of form” in the discrete, three-dimensional
folding patterns of protein molecules. The folds can be
classified into a finite number of structural families that are
determined by natural law, not natural selection—much
like the physical laws that give rise to atomic elements in the
periodic table. Writing for the Journal
of Theoretical Biology, his team
describes the protein folds as “‘lawful
forms’ in the Platonic and pre-DARWINIAN sense of the
word, which are bound to occur everywhere in the universe where
the same 20 amino acids are used for their construction”
(DENTON/MARSHALL/ LEGGE 2002). In another piece, for Nature, DENTON and
MARSHALL argue: “If forms as complex as the protein folds
are intrinsic features of nature, might some of the higher
architecture of life also be determined by physical law?”
(DENTON/MARSHALL 2001).
Moreover, given the limitations of a
material world of flux, DENTON considers the possibility that
“the laws of nature are fit for only one unique thinking
being capable of acquiring knowledge and ultimately
comprehending the cosmos” (DENTON 1998). He cites Mark
WARD’s research on the fine balance achieved (1) between
the size/number of neurons and the blood vessels which nourish
them, and (2) between the width of axons and the required
insulation/ blood supply (WARD 1997). Referring to this and to
the staggering compaction of synaptic connections in the human
brain, he writes that “the evidence is certainly
consistent with the possibility that the human brain does
indeed represent the most advanced information-processing
device that can be built according to biological
principles” (DENTON 1998).
However, to say that the experience of
consciousness is fully explained by the physical laws that
produce such a brain is a non sequitur, except to committed
reductionists. Physicists from Brian PIPPARD to Stephen
WEINBERG have raised questions about the reasonableness of
expecting consciousness itself11 to ever be subsumed under the
domain of physics and chemistry (PIPPARD 1992; WEINBERG 1992,
p44). Given a complex structure with ample computing power,
should a theoretical physicist be able to deduce the existence
of self-awareness from laws of physics? Cognitive scientist
David J. CHALMERS suggests that the problem of trying to derive
consciousness from physical laws is so troublesome that any
final theory of physics “must contain an additional
fundamental component”. He proposes “that conscious
experience be considered a fundamental feature, irreducible to
anything more basic” (CHALMERS 1995).
Concluding Options
If nature is somehow rigged in favor of
mind, then the tremendous odds against our existence disappear.
But if that concept were to catch hold in scientific circles,
Paul DAVIES claims that it would create a “decisive
shift” in science (DAVIES 1999, p263), reversing a
300-year trend toward reductionist thinking. We cannot at the
same time hold to the Principle of Mediocrity and to the idea
that human cognition is a bizarre case.
The evidence surrounding the discovery of
the earliest craniates forces us to choose between renouncing
one of two deeply embedded traditions of modern science. Either
mind plays a role in nature by necessity, which appears to
contradict the reductionist basis for doing science—or
mind plays no role and has appeared as an “oddball
rarity”, which contradicts science’s equally
cherished Copernican Principle. This means that our first two
original options —human-level cognition as either an
accidental, or a law-like, process—will give us serious
problems either way we choose. If we choose the lawful process
option, we must then ask ourselves: What kind of law will
ensure that primates (or any other form preadapted for
braininess) will survive through the bottleneck of contingent
events that are beyond the control of any known natural
mechanisms?
To opt for human-level cognition as both
accidental rarity and commonplace occurrence is to render both options
meaningless, since they contradict each other. We do have a
third option: that our existence is primarily due to neither
accident nor cosmic law. To speak awkwardly, as we did at the
beginning of this article, of the human-level cognition
“observed” on Earth is to flagrantly ignore our own
unique position as both observer and the observed. The inside
information we’re privy to as conscious and frequently
conscientious primates may provide some hints about the
workings of chance and natural law, for our lives would seem to
be, from our own viewpoints, composed of more than either
accidents or laws. From an unlikely combination of
circumstances have emerged beings who are much more than the
sum of their parts. It would seem that our most uniquely human
abilities are not predictable in any detail from our
morphologies.
If we say that we transcend our physical
world with our human achievements—our music, literature,
humor, love—it still remains for us to decide whether
this transcendence emerged by accident or according to a prior
purpose. Simon CONWAY MORRIS suggests that this may be the
principal reason that biologists have hesitated so long to
explore directionality and channeling: “If evolution is
in some sense channeled, then this reopens the controversial
prospect of a teleology; that is, the process is underpinned by
a purpose”. (CONWAY MORRIS 1998, p14). And he notes a
growing trend to bring cosmology’s Anthropic Principle
down to our biosphere. CONWAY MORRIS sees humanity’s
uniqueness in our ability to make these kinds of choices—
and voices his irritation with those who choose to live
irresponsibly based on an assumption of life’s
purposelessness (Ibid). The reductionist’s belief in
human life as a cosmic accident is a metaphysical commitment
too.
After all, at least to this point, the
most dazzling thing on Earth that evolution has done is to
produce volitional beings whose present lives have little to do
with the physical processes that brought them.
“Uniquely”, CONWAY MORRIS writes, “there is
inherent in our human situation the possibility of
transcendence” (Ibid). The fact that it’s only a
possibility speaks volumes, once again, about the human
capacity to choose.
Acknowledgements
I wish to thank the referees for providing
many useful suggestions for improvement of this manuscript. I
also thank Jun-Yuan CHEN, Nanjing Institute of Geology and
Palaeontology, and Paul K. CHIEN, University of San Francisco, for generously
contributing photographic materials and diagrams.
Notes
1 Biological
dictionaries now frequently replace the subphylum name Vertebrata by the
newer, broader phylum name Craniata
in order “to represent the
distinguishing characteristics more accurately” (RUDIN
1997). Chief among craniate distinctions is a manifest head
containing a brain and sensory organs. Modern craniates are
also characterized, as vertebrates were, by a segmented
vertebral column. The group continues to include fish,
amphibians, reptiles, birds, and mammals. In modern cladograms,
the Chordata clade includes the Craniata
clade, the Craniata clade includes
the Vertebrata and Myxinoidea clades, etc.
2 The
following distinction is made here between cognition and intelligence: Cognition is used to describe the application of mental
processes involved in knowledge; while intelligence describes the
ability to know, regardless of its use. Cognition is the act of
using of one’s intelligence. Thus the human capacity for thought and reason
called intelligence results in human-level cognition, an awareness
involving reasoning and judgment apparently unlike the mental
processes of any other animal on this planet. Human- level
cognition should be detectable, since it tends to find
expression in human-level communication, engineering feats,
abstract and mathematical problem-solving, musical
compositions, fine art, literature, science, etc.
3 That is, the
evolution of human-level cognition is dependent upon a long
series of unpredictable, historical events, making its
occurrence on Earth a rarity. If other planets harbor life,
only a very tiny fraction, if any, would then be expected to
host human-level-or-higher cognition.
4 One might
argue for a fourth option: that human-level cognition exists as
both a rare fluke and a common or lawlike property of the universe;
but the statements can both be true only by rendering them
meaningless. While there is nothing logically contradictory
about chance mutations (flukes) and natural selection (law)
working together to produce novel forms of life, the question
here is whether it is rare or common for any such combination
of law and chance to produce forms that result in human-level cognition. When referring to the evolution of cognition, the
first two hypotheses are contradictory and do not allow for
both as a primary cause.
5 The terms body plan and Bauplan are
generally used interchangeably. James VALENTINE applies the
term Bauplan to “the upper levels of the taxonomic
hierarchy” where “phyla- or class-level clades are
characterized by their possession of particular assemblages of
homologous architectural and structural features”
(VALENTINE 1986). Wallace ARTHUR identifies six morphological
characters to distinguish animal body plans: skeleton,
symmetry, pairs of appendages, body cavity, cleavage pattern,
and segmentation (ARTHUR 1997, p27). Like others, ARTHUR tends
to identify animal body plans in the Cambrian period with the
animal phyla (he speaks of the Cambrian “origin of the 35
or so animal body plans” (ARTHUR 1997, opening page),
though in more general contexts (non-Cambrian) he speaks of
“phylum/ class level body plans” (ARTHUR 1997,
p27).
6 Developmentalism:
emphasizes the importance of
understanding ontogeny—the history of, and the genetic
processes involved in, the development of the individual
organism—for understanding evolution. Neo-DARWINISM: emphasizes natural
selection and mutations as the overwhelming driving forces for
understanding evolution. Also called the Modern Synthesis
(since it synthesizes these two mechanisms). Formalism: emphasizes
internal constraints toward the evolution of particular body
forms. Functionalism: emphasizes external adaptations as the primary
force behind the production of characters that function best in
particular environments. Punctuationalism:
emphasizes the geologically abrupt
origin and subsequent stasis (“equilibrium”) of
most species. Gradualism: emphasizes the slow and constant accretion of
small changes that eventually add up to larger changes and
separations between organisms. Top-down
theory: emphasizes the evolution of
the higher taxa first, so that the most widely separated groups
appear early, and “the diversification of the phyla
occurs before that of classes, classes before that of orders,
orders before that of families” (ERWIN/VALENTIN/SEPKOWSKI
1987). Bottom-up theory: emphasizes the evolution of the higher taxa from
the accumulation of lower taxa, creating a phylogenetic tree of
increasing diversity and eventual disparity.
7 Reductionism
is a philosophical method of explaining a complex set of facts
by reducing them to a set of smaller, simpler facts; the whole
should be predictable from its smaller, constituent parts.
8 Constraints may be negative or positive; negatively, they
are restrictions on evolution’s direction; positively,
they are preferred directionality of variation; either internal
or external factors may constrain evolution toward particular forms. Channels are usually
positive, internal, preferred evolutionary pathways.
9 Convergence is the explanation for shared characters of
independently evolved organisms. In GOULD’s lexicon, the
convergence of characters is based upon common external
adaptations. He carefully distinguishes convergence from parallelism, which
is the independent origin of common features channeled by internal constraints
of homologous genes or developmental pathways. Other scientists
frequently employ the term convergence
to include any case where the
evolution of characters repeats itself, whether explained by
external constraints or internal channeling.
10 Disparity is the word usually used to describe differences
between organisms that involve whole body plans; diversity is
reserved for differences between lower-taxa organisms,
especially at the species level (GOULD 1989, p49).
11 WEINBERG
distinguishes between “consciousness itself”, the
self-awareness/feelings experienced by humans, and
“correlatives to consciousness” that may be
examined in terms of brain waves, electrical activity, hormones
in the blood, etc. (WEINBERG 1992, p44).
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