“Was the first craniate on the road to cognition?”
Evolution and Cognition 2003; 9(2):142-156.
Fredric J. Heeren (Page 4)
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).
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.
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.
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).