Fred Heeren, Evolution and Cognition Journal

Top-Down Evolution

The appearance of chordates at this early date adds to the evidence for what Berkeley paleobiologist James VALENTINE and his colleagues call a “topdown” pattern in the fossil record (ERWIN/VALENTINE/ SEPKOWSKI 1987). In the most published diagram in the history of evolutionary biology (and the only diagram in On the Origin of Species), DARWIN illustrated what became the standard, bottom- up view of how new taxa evolve (DARWIN 2000, pp514–515). Beginning with small variations, evolving organisms diverge further from the original ancestor, eventually diversifying into new species, then new genera, new families, new orders, and the splitting continues until the highest taxa are reached, which are separated from one another by the greatest differences (DARWIN, p120, p128; SIMPSON 1953, pp383–384).

“The textbooks all teach that evolution takes place when a new species appears, when the morphology is very close”, said CHEN in a talk titled “Top-Down Evolution and the Fossil Record” (CHEN 1999). “But that story is not true, according to our fossil finds”, he told the assembled scientists. “The new phyla make their start in the early days, instead of coming at the top”. He pointed to a very different-looking diagram of his own to illustrate the fact that morphological gaps among animals were greater near the beginning and less significant later (LEWIN 1988; ARTHUR 1977, pp81– 82; SCHWARTZ 1999, p3) (Figure 4).

Rather than observing one body plan branching out into greater numbers of body plans over geologic time, paleontologists instead note maximum disparity10 between body plans from the beginning, and the retention of essential characters within each throughout geologic history, while increasing diversification occurs at successively lower hierarchical levels; (VALENTINE 1986; PADIAN/CLEMENS 1985; BERGSTRÖM 1994). Developmental geneticist Stuart KAUFFMAN sees deeper reasons for the pattern than anything neo-DARWINISM knows: “the patterns of the branching, dramatic at first, then dwindling to twiddling with details later, are likely to be lawful” (KAUFFMAN 1995, p14).

After listening to CHEN’s “top-down” talk, paleontologist David BOTTJER said, “I think the Cambrian explosion is going to tell us something different about evolution, in the sense that it’s not the same story that we have always been taught” (BOTTJER personal communication). BOTTJER can’t argue with the top-down pattern: “After the concentration of phyla first showing up in the Cambrian”, he said, “then we see classes, then orders, families, and that’s where much of the action is later on, after the Cambrian. So there is that kind of a pattern. And the question is, why is that happening?” Participants in the Kunming symposium came prepared to propose new, sometimes non- DARWINIAN mechanisms to explain the relatively abrupt appearance of the phyla.

New explanations included: saltatory evolution as a reaction to submarine hydrothermal eruptions (YANG et al. 1999); a “Cambrian substrate revolution” in which burrowing animals destroyed the microbial mat habitat of others, resulting in new environments and extensive adaptations (BOTTJER 1999); a billion years of genetic preadaptations for complex metazoans through “set-aside cells” (DAVIDSON 1999); “intelligent design”, the inference that the preadaptations and “appearance of design” point to an actual design by an intelligent entity, whether that entity be explained by directed panspermia, a Platonic demiurge, a theistic deity, or some other, unknown intelligent cause (NELSON 1999; WELLS 1999); the evolution of Platonic forms as a vitalistic process, i.e., the suggestion that evolution is driven by a controlling force or principle within organic forms that cannot be reduced to physics and chemistry alone (DENTON 1999); and top-down evolution, in which laws of harmony play at least as great a role in evolution as competition (CHEN 1999).

Contingency

Returning to our original three hypotheses, we now ask: How do findings surrounding the earliest known craniate affect probabilities for the evolution of cognition? Cephalization prior to the development of an internal body support structure might suggest a body plan in which the head is in some sense dominant. Observing the top-down pattern in the subsequent fossil record, some might further see in this a law-like process dictating an early appearance of brainy chordates among the body plans. But what kind of natural law would demand that, of all the evolving phyla, one of them would necessarily develop a conspicuous brain, ready to be subsequently supported by the vertebrate structure?

Worse, what kind of law would demand that such a pre-backbone craniate would necessarily survive what Stephen Jay GOULD calls “the Burgess decimation”? (GOULD 1989, pp233–239). In Wonderful Life, he suggests that “a 90 percent chance of death would be a good estimate for major Burgess [Cambrian] lineages” (p47). In recent years, Peter WARD and Donald Brownlee have stirred up controversy about the odds against complex life (even as complex as a flatworm) evolving on another planet. In their book Rare Earth, they argue that complex life in the galaxy may be rare, mainly because of the small number of planets that provide enough time and the right conditions for its evolution (WARD/ BROWNLEE 2000). They also believe that the Cambrian explosion of so many new, widely separated, complex animal groups didn’t have to happen. Neo- DARWINISM doesn’t predict such an event. And the fact that virtually no new animal phyla have evolved in the 530 million years since should give us pause (VALENTINE 1995).

The new discoveries in China take this concern a step further, demonstrating that even a “charmed place” like Earth, apparently ideal for life, is not necessarily good enough to produce advanced intelligence. First we learn that chordates, like the other animal phyla, must evolve early to evolve at all (since new phyla don’t keep appearing after the Cambrian). Then we learn that major groups did not survive the Cambrian, though we know of no reason why they were less fit than chordates. The first fact (all body plans forming close together in time) has a law-like quality about it, while the second (extinctions) appears highly stochastic.

GOULD may have been overenthusiastic in his use of the term “Cambrian decimation” (GOULD 1989, p47), and we should not infer that chordates only had once chance in ten to survive the Cambrian. To say that most lineages disappeared is not to say that most phyla disappeared. We do not know that the Cambrian ended with a massive extinction event, as we do about the end of five other periods. However, some analyses show that more disappearances occurred by the end of the Cambrian than at the end of any of the “Big Five” extinctions (WARD/BROWNLEE 2000, p184)—even the Permian, usually declared to be the most catastrophic. According to independent studies by paleontologists Helen Tappan and Norman Newell, about 60 percent of marine families went extinct in the Cambrian, compared to about 55 percent in the Permian” (Ibid).

What we can say with certainty is that craniates had their birth in the most dangerous possible period in the history of metazoan life. As has long been known, in only one period do the number of animal phyla decrease: the Cambrian, and in that period they decrease drastically (DOBZHANSKY et al. 1977, pp421–23). Cambrian researchers say that this period was by far the riskiest because species diversity within each phylum was at an all-time low, making it easier for changing environmental conditions to destroy an entire phylum merely by eliminating a few species (GOULD 2002, p1315). But as geologic time progresses, there is a pattern of increasing diversity at lower taxonomic levels relative to the higher taxa. Today there are far fewer classes and orders than existed four- to five-hundred million years ago, while there are probably eight to ten times the number of species (Dobzhansky et al. 1977, p428).

Thus the same phenomenon that gives rise to the top-down pattern in the fossil record also helps to explain why GOULD considered the chordate’s Cambrian survival a momentous event, like winning the lottery. And what reason can we give for expecting our winning streak to hold up through all the subsequent chancy events, including at least five major extinctions? Perfectly fit species were caught by chance at the wrong time, belonging to groups that would not otherwise have gone extinct, but that simply happened to be at a low point in species numbers (since species numbers fluctuate randomly over time) (GOULD 2002, pp1312–1317). The K-T impact that was apparently ultimately responsible for exterminating the dinosaurs 65 million years ago happened to work in favor of small mammals. But what if that extraterrestrial impactor had missed the Earth? Might dinosaurs have ruled the planet for another 200 million years, preventing the evolution of cognition?

The Principle of Mediocrity

Such an idea appears to challenge the Principle of Mediocrity (also known as the Copernican Principle), the assumption that there is nothing special about our place in the universe. After all, the universe does not revolve around Earth. Our planet, our solar system, even our galaxy is but one of billions. Applied to our subject, the Principle of Mediocrity implies that if human-level cognition exists here, it must exist commonly throughout the universe.

What astronomers know by principle and by multiple proofs, biologists are anxious to demonstrate too. Suspecting that we self-aware beings shouldn’t be exceptional, biologists and paleontologists are beginning to contemplate new ways to beat the odds. A few even wonder if the game is somehow rigged. This seems to be Jun-Yuan CHEN’s position, and a theme of his “top-down” talk at the Kunming conference: the fossil record demonstrates something more than accidental progress by a series of flukes.

Rather than seeing a gradual accumulation of small modifications that finally added up to widely separated animal groups, CHEN observes an explosive appearance of particular forms—sophisticated, widely separated animal groups, right from the start. Diagnostic characters did not accrue over time, but showed up with their first appearance in the form of Bauplans, including our own (CHEN 1999; BERGSTRÖM 1994). To say that this was not in some sense “meant to be” would seem to be a denial of this important, Copernican axiom of science.

Cognition in Other Body Plans?

Haikouella demonstrates that the basic body plan that sets us so far apart from mollusks and arthropods was in place at the beginning of the animal fossil record. Chordates, named for the notochord that would eventually be largely replaced and surrounded by the vertebral column, seem ideally suited to provide the structure required to put sensory organs up high, where they can help an animal get the best perspective on surroundings. Other design requirements for brainy wannabees naturally follow: the brain needs to be near these sensory organs, to minimize reaction time, and the whole should be protected by an encasement. A distinct head is thus a part of the package, which CHEN and SHU claim to have found in these earliest “craniates”. But again, the very considerations that make this animal appear to be optimally placed also make its position look tenuous.

Consider a world where chordates had gone extinct with other Cambrian animals. GOULD considers this to be a likelier scenario, a world without fish, birds, reptiles and mammals. Instead, lots of sea stars, crustaceans, insects, and worms. But, we ask, couldn’t chordates have re-evolved later? Not when we recall that, with the possible exception of Bryozoa (“moss animals”), no new animal phylum has ever evolved since the Cambrian period (VALENTINE 1995). If advanced intelligence was to evolve after that, it would have had to take a radically different form.

In that case, wouldn’t another animal group have filled our niche to eventually develop the ability to compose literature and do math? Again, not likely. Biologists have reasons to doubt that other phyla are so well suited to developing large brains situated in a commanding position. For a simple thought experiment, readers should try to picture a sea star, bug or worm with a big head. Or, more to the point, readers might try to think of a member of a non-chordate phylum on this planet that did develop a written language and technology, given 500 million years to do so.

Paleobiologist Michael BENTON points out that “the vertebrate design lends itself to the development and protection of a brain. This organ is present in other animals, but there are limits on its growth—one of them imposed very early in the history of life, when animals were first developing basic equipment like a front and a back, sense organs, and the ability to use information from the sense organs …” (BENTON 1993). BENTON notes the importance of the right architecture to create space available for the cluster of nervous tissue where data arrive and orders depart. While vertebrates separate this central ganglion from the rest of the body, arthropods and mollusks wrap it around their gut. Observes BENTON: “Any tendency for this tissue to grow is likely to squeeze the tube of the gut and constrict the supply of food. This is a contradiction that the arthropod design has never resolved…” (Ibid).

What if chordates survived, but not mammals or primates? Some might argue that, given more time, dinosaurs themselves could have developed high intelligence. Paleobiologists, however, say that a wholly different kind of skull would be required. “You cannot simply grow a giant brain in a dinosaur like Velociraptor: you have to reconstruct the skull”, writes Richard FORTEY. “Consciousness is not a clever trick to be whipped up from any set of neurons like a soufflé from an egg” (FORTEY 1998).

Partly because our present existence appears to depend upon a long string of unpredictable accidents, biologists know of no fundamental “law of progress” to show them why the path should have led to anything like Homo sapiens. Biologist C. O. LOVEJOY writes that “the evolution of cognition is the product of a variety of influences and preadaptive capacities, the absence of any one of which would have completely negated the process” (LOVEJOY 1981). He notes that the human’s complex nervous system is actually a reproductive liability, requiring a longer gestation period and a longer time to train the young. LOVEJOY concludes: “It is evident that the evolution of cognition is neither the result of an evolutionary trend nor an event of even the lowest calculable probability, but rather the result of a series of highly specific evolutionary events whose ultimate cause is traceable to selection for unrelated factors such as locomotion and diet” (Ibid).

“If intelligence has such high value”, writes Ernst MAYR, “why don’t we see more species develop it?” (MAYR 1996). He contrasts the singular development of high intelligence with the repeated evolution of sight, which occurred at least 40 times (SALVINI-PLAWEN/MAYR 1977). He calls the search for extraterrestrial intelligence “hopeless” and “a waste of time”, concluding that “for all practical purposes, man is alone” (MAYR 2001, p263).

The list of leading biologists and paleontologists on record for defending this intelligence-by-fluke position is impressive, including SIMPSON, DOBZHANSKY, FRANCOIS, AYALA, and GOULD (BARROW/ TIPLER 1986, p133). British astronomer John BARROW and American physicist Frank TIPLER note that “there has developed a general consensus among evolutionists that the evolution of intelligent life, comparable in information-processing ability to that of Homo sapiens, is so improbable that it is unlikely to have occurred on any other planet in the entire visible universe” (Ibid).

Many astronomers who once took optimistic positions on the probability of finding signals from an extraterrestrial intelligence are adjusting their predictions. Forty years of null SETI results may have even taken their toll on optimist Robert JASTROW, director of the Mt. Wilson Observatory. Though he once told this writer, “We’ll be hearing from those guys soon”, he has since modified his statement to “If life is common, we’ll be hearing from those guys soon” (JASTROW personal communication). Even this guarded claim shows an astronomer’s willingness to believe that the route from life to intelligence is an obvious one, which, as we have seen, is disputed by most biologists and paleontologists schooled in the Modern Synthesis.