But we found that the numbers don’t support this facile tale. Clams and brachiopods do not show the fine-scale negative interaction that wedging requires. In fact, they vary in sympathy throughout geological time: periods with more than an average number of clams are enriched in brachiopods as well; stages deprived of brachiopods are also weak in clams. Moreover, each group seems to follow its own distinctive course in normal times, oblivious to the other’s fate and history: clams increase slowly within each chunk of normal time; brachiopods hold their own.
The old story represents a false inference from one basic fact: brachiopods do dominate early faunas, while clams are so abundant today that Ho Jo can feed a nation on their breaded feet. But we found that the supposed “replacement” of brachiopods by clams does not occur by gradual competitive wedging, but simply records different reactions to that greatest of all mass dyings—the Permian extinction (when more than 90 percent of species probably perished). Brachiopods really took it on the (metaphorical) chin; clams scarcely noticed the debacle. Thus, clams got “ahead” of brachs in this one geological moment and never relinquished their new incumbency. The fossil pattern records independent reactions to a single mass extinction, not gradual wedging and triumph of superior anatomies. Clams and brachiopods act like ships passing in the night, but faring differently in the great tempest.
In short, if mass extinctions are so frequent, so profound in their effects, and caused fundamentally by an extraterrestrial agency so catastrophic in impact and so utterly beyond the power of organisms to anticipate, then life’s history either has an irreducible randomness or operates by new and undiscovered rules for perturbations, not (as we always thought) by laws that regulate predictable competition during normal times.
All this ferment may be disturbing to our hopes and our desires to find a sop or solace in nature, but it presents paleontology with the richest possible field for thought and action. For we students of life’s history are guardians of the data that can resolve these fundamental issues. The cyclical theory of catastrophic extinction leaves paleontologists in the driver’s seat with a decade of exciting work before us. Scientists rarely have the privilege of addressing such fundamental questions in a new and fruitful manner.
I cannot, in this context, present a technical program for paleontological work, but consider just three issues demanding attention and amenable to resolution from the fossil record:
How much of the 26 million years between catastrophes does life need to recover its former richness (in numbers of species and ecological complexity of communities)? If most time passes in periods of recovery, then competitive models must fail (since they require a full world for the wedge’s metaphor) and external triggers must drive life’s history.
Are patterns of who dies and who survives a catastrophe consistent with purely random removals from the field of life? If randomness fails, do the regularities of mass extinction record rules different from those governing the order of normal times between catastrophes? Under either a random or “different rules” model, the Darwinian hope of smooth extrapolation from small-scale events (which can be studied directly) to the great geological panorama fails, and we must recognize the distinctive character that mass extinction imparts to life’s history.
Why are the cyclical extinctions so different in strength (one wiping out more than 90 percent of species, others protruding so little above background that we needed Sepkoski’s refined data to recognize them at all)? Some cometary enthusiasts, in the wave of overattribution that accompanies most new ideas, are trying to explain everything by impact. If perturbations of the Oort cloud send billions of comets hurtling toward the planets, only a handful will strike the earth—sometimes more, sometimes fewer. Big extinctions mean more comets; little extinctions, fewer. But it cannot be so mechanically simple. We have compiled a century of data on correlations of terrestrial events with mass extinctions (many, for example, are accompanied by falling sea levels); we also know that several extinctions were preceded by long, gradual, and simultaneous declines in many groups. We used to think that these terrestrial correlates would explain the extinctions. I suspect that we need a reversed perspective, but one that will still cherish the terrestrial data. Terrestrial correlates are probably not the causes but the primary regulators of severity. When comets hit a biosphere weakened for other reasons, unusually large extinctions ensue. The greatest of all extinctions occurred on an earth with all continents coalesced into a single Pangaea. I used to think that Pangaea was the primary cause (see essay 16 in Ever Since Darwin); I now think that it was the stage for maximal severity.
To end these universal bangs with a personal whimper, may I make my little suggestion to astronomical colleagues pursuing the good search. If Thalia, the goddess of good cheer, smiles upon you and you find the sun’s companion star, please do not name it (as you plan) for her colleague Nemesis. Nemesis is the personification of righteous anger. She attacks the vain or the powerful, and she works for definite cause (punishing Narcissus, for example, with his burden of unquenchable self-esteem). She represents everything that our new view of mass extinction is struggling to replace—predictable, deterministic causes afflicting those who deserve it. She would also place one more Western figure into a universal sky. May not one member of our solar system honor the traditions of another culture?
Mass extinctions are not unswervingly destructive in the history of life. They represent a source of creation as well, especially if the second view of external triggering has validity, and the Red Queen of internal competition does not drive life inexorably forward. Mass extinction may be the primary and indispensable seed of major changes and shifts in life’s history. Destruction and creation are locked in a dialectic of interaction. Moreover, mass extinction is probably blind to the exquisite adaptations evolved for previous environments of normal times. It strikes at random or by rules that transcend the plans and purposes of any victim. May we not name the sun’s potential companion for a figure who embodies these central features of creativity in destruction and “neutrality” toward the evolutionary struggles of creatures in preceding normal times?
Siva, the Hindu god of destruction, forms an indissoluble triad with Brahma, the creator, and Vishnu, the preserver. All are enmeshed in one—a trinity of a different order—because all activity reflects their interaction. A. Parthasarathy writes in his Symbolism of Hindu Gods and Rituals: “All three powers are manifest at all times. They are inseparable. Creation and destruction are like two sides of a coin…. Morning dies to give birth to noon. Noon dies when night is born. In this chain of birth and death the day is maintained”—as the balances of life’s history arise from creative recoveries following massive destructions.
The Hindu god Siva in the form of Nataraja. He holds the flame of destruction in one hand, and a drum to regulate the rhythm of the dance (and symbolize creation) in another. He moves in a ring of fire—maintained by the interaction of creation and destruction. THE ASIA SOCIETY, NEW YORK. MR. AND MRS. JOHN D. ROCKEFELLER 3RD COLLECTION. PHOTO BY OTTO E. NELSON.
Siva is often, and most beautifully, presented in the form of Nataraja, the cosmic dance. He holds in one hand the flame of destruction, in another (he has four in all) the damaru, a drum that regulates the rhythm of the dance and symbolizes creation. He moves within a ring of fire—the cosmic cycle—maintained by an interaction of destruction and creation, beating out a rhythm as regular as any clockwork of cometary collisions. “In this perpetual process of creation and destruction,” Parthasarathy writes, “the universe is maintained.” Unlike Nemesis, Siva does not attack specific targets for cause or for punishment. Instead, his placid face records the absolute tranquillity and serenity of a neutral process, directed toward no one but responsible for maintaining the order of our world.
Most hot ideas turn out to be wrong. I can only hope that I will not be remembered as the man who campaigned with a name for the nonexistent (surely worse than a moon for the misbegotten). Some chanc
es are certainly worth taking. If Thalia smiles and Siva exists, think what it all will mean for my beloved science of paleontology. We have labored so long under the onus of boredom and dullness. We are the guardians of life’s history, but we are often depicted as mindless philatelists of stone; specialists in tiny corners of space, time, and taxonomy; purveyors of such arcane names as Pharkidonotus percarinatus in extended orgies of irrelevant detail. The editors of Britain’s leading scientific journal wrote of us in 1969: “Scientists in general might be excused for assuming that most geologists are paleontologists and most paleontologists have staked out a square mile as their life’s work.”
Times have been changing for more than a decade, but Siva would crown our transformation. What an apotheosis for a previously “dull” science—to be the source and impetus, by discovering the 26-million-year cycle, for the greatest revision of cosmology (at least for our little corner of the heavens) since Galileo.
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