How We Believe_ Science and the Search for God - Michael Shermer [134]
I am not speaking of randomness, but of the central principle of all history—contingency. A historical explanation does not rest on direct deductions from laws of nature, but on an unpredictable sequence of antecedent states, where any major change in any step of the sequence would have altered the final result. This final result is therefore dependent, or contingent, upon everything that came before—the unerasable and determining signature of history. [Emphasis added.]
As Gould notes, contingency is an unpredictable sequence of antecedent states, not randomness, chanciness, or accident.
Daniel Dennett likewise takes Gould to task in a chapter entitled “Tinker to Evers to Chance,” a play on words linking Gould’s love of baseball—the three names represent the most famous double-play combination in baseball history—to chance, which Dennett identifies with contingency. But contingency does not mean chance, nor does it mean random, despite Dennett’s conclusion: “The fact that the Burgess fauna were decimated in a mass extinction is in any case less important to Gould than another conclusion he wants to draw about their fate: their decimation, he claims, was random.” True, mass extinctions may seem random, as when an asteroid hits the Earth. But by contingency Gould means a conjuncture of preceding states that determine subsequent outcomes. Just as astronomers knew exactly when and where Comet Shoemaker-Levy 9 was going to strike Jupiter in July of 1995 (and nailed the timing and location precisely), astronomers from (say) Mars, observing Earth 65 million years ago could have calculated the collision with the Yucatán peninsula with pinpoint accuracy. But the effects of those impacts could not have been adequately computed (and in the case of the Jupiter hit were not), because of the number of contingencies involved.
The eventual rise of Homo sapiens, is even more contingent with millions of antecedent states in our past. Each event in the sequence has a cause, and thus is determined, but the eventual outcome is unpredictable because of contingency, not randomness or chance. The Burgess extinction may have been determined, but the sequence of events leading up to it, and those following, all the way to humans, were contingent. On this point Dennett says he is confused about what Gould means by “we” when he says we would not be here again if we reran the tape:
There is a sliding scale on which Gould neglects to locate his claim about rewinding the tape. If by “us” he meant something very particular—Steve Gould and Dan Dennett, let’s say—then we wouldn’t need the hypothesis of mass extinction to persuade us how lucky we are to be alive … . If, at the other extreme, by “us” Gould meant something very general, such as “air-breathing, land-inhabiting vertebrates,”he would probably be wrong.
Dennett’s confusion seems, well, confusing. By “we” Gould means the species Homo sapiens, no more, no less, and he has stated so on numerous occasions, including in Wonderful Life: “Replay the tape a million times from a Burgess beginning, and I doubt that anything like Homo sapiens would ever evolve again.”
One might claim that these misunderstandings are caused by the fact that Gould has not offered a formal definition of contingency. That is true, so one must read him broad and deep. But it is there in dozens of examples and several informal definitions. In his essay “The Panda’s Thumb,” Gould shows that the thumb—actually the radial sesamoid bone of the panda’s wrist—is not a predictable design of nature’s necessitating laws of form, but an improvised contraption constructed from the history of what came