Stray Thoughts on Contingency Following the MBL-ASU History of Biology Seminar — Extinct

I am not going to attempt a summary or digest of the week’s activities here. That was the unenviable task given to Roberta Millstein, and perhaps a future edited volume will contain a polished version of her remarks. There is one task I can’t sidestep however. Historical contingency—now what exactly is that? If I tell you that we failed to answer this question over a week of discussion, you will hardly fall out of your chair. Still, it is worth lingering on the question for a moment.

To say that something—an event or outcome—is historically contingent is to say, at least, that it could have been otherwise. It could have been the case that no roads in Woods Hole were named for Chicago biologists. Or that no such place as Woods Hole ever existed. (Imagine if the Laurentide Ice Sheet had not reached modern-day Massachusetts. Then there is no such thing as Cape Cod, and no Woods Hole either.) Something that could not have been otherwise is not contingent, it is necessary. It is true in all possible worlds, if you’re into that sort of thing.* A contingent outcome is true in only some possible worlds. I am being a bit sloppy here, but the basic point ought to be clear. Contingent outcomes are distinct from necessary ones. This is what we might call a “minimal sense” of contingency.

[* Actually, the things that are supposed to be true in all possible world are necessary truths: truths of logic, say. In discussions of contingency in evolution, the sense of necessity in view is different. It refers to “physical necessity,” or something like that: the kind of necessity underwritten by laws of nature. Something that is physically necessary in our world will not be physically necessary in all possible worlds—it will only be necessary in those worlds whose laws of nature resemble our own.]

Minimal contingency is all well and good. But especially in discussions of contingency in evolution, the term “contingency” carries an whiff of improbability. It is not just unnecessary that there are two streets in Woods Hole named after Chicago biologists. It is also unlikely, contingent on a slew of historical details lining up just right. Had one or a few of these details been misaligned, then the outcome would have failed to obtain and another, rather different one would have taken its place. To label an outcome “contingent,” then, is to draw attention to the sequence of unique events (or “contingencies”) required to bring it about—it is not just to flag that it could have been otherwise.

Discussions of contingency in the life sciences are probably as old as biology itself, but when it comes to discussions of contingency per se, an important touchstone is Wonderful Life. This is the book that Stephen Jay Gould published in 1989. It is perhaps best remember for popularizing the expression “replaying life’s tape,” which also supplied the name for our seminar. The associated thought experiment runs as follows. Imagine you are able to “rewind the tape of life” and play it again from scratch. During this “replay,” the history of life as you know it will be erased and written over with something new. But what exactly? How closely will this new history of life resemble the old one, both in its broad contours and its intimate details? And—since one detail interests us most of all—how likely is it that human-like intelligence will evolve anew? Gould’s answer to the last question is a bracing, “not very.” In fact, “any replay of the tape [will] lead evolution down a pathway radically different from the road actually taken.” Evolution is a historical process, and the “essence of history” is contingency. This seems to indicate that human intelligence is a cosmic accident that almost certainly would not reappear if the history of life could be run back to the beginning and allowed to unfold again under the same or similar conditions.

There are many difficulties involved in interpreting what Gould is up to. I’m not going to rehearse these here (for those interested in the details, I recommend that you check out John Beatty’s post from 2017, which I recently re-posted in honor of the seminar). Instead, I want to consider an issue that did not arise during our discussions at MBL. That is: just how effective is Gould’s argument, anyway? By this I don’t mean how effective is it scientifically. Gould’s argument is a scientific argument—it is an argument that the history of life would unfold very differently if the “tape of life” could be run again from the Cambrian radiation. (The whole thing is strung together with gossamer threads of intuition, but that is not my present complaint.) No, what I am interested in is how effective the argument is as a broadside against anthropocentrism: the view that humans are the most important things in the world.

As Derek Turner suggested at the seminar, a central aim of the “replay experiment” is to undermine anthropocentrism by severing its connections with evolutionary theory. Gould takes it to be a comforting thought that humans are the inevitable result of a progressive evolutionary process—a process that, left to its own devices, was bound to produce something like a human mind. The replay experiment seeks to eliminate this conceit by showing that humans are thoroughly accidental. Take one wrong turn on the evolutionary path leading to humans and bam!—not only are humans erased from the subsequent history of life, but so is the best chance of producing anything resembling a human mind. (Gould really thinks this. The last pages of Wonderful Life walk readers through a series of counterfactual scenarios. What if the eukaryotic cell hadn’t come together? What if the Ediacaran biota hadn’t gone extinct? What if a different set of anatomical designs had swum through to the Ordovician Period? Etc. At each check-point, the unrealized possibility erases humans—and I gather, anything resembling a human mind—from the subsequent history of life.)

All this has the desired effect of making human-like minds seem far from inevitable. Indeed, by the end of the exercise, Gould has made them seem next-to-miraculous. But isn’t this perhaps a bit of a problem? Maybe Gould is right that some people take solace in the idea that human minds emerged inevitably from a progressive evolutionary process. I can imagine a liberal theologian from the early part of the twentieth century taking this view. (Why did God set up the universe in the way He did? Because He knew it was bound to produce human-like minds in their multitudes.) However, I submit that what is more conducive to human arrogance is the notion that humans are just extra special things. Perhaps we are improbable—okay, fine—but if the reason is that something so utterly unique is hard to pull off, then human arrogance escapes unscathed. Ask yourself, which of these is more damaging to human arrogance: the notion that we are improbable because our defining feature is incredibly difficult to evolve, or the notion that we are ordinary products of evolution, brainy but not miraculous? Gould opts for Door A, and, I think, stubs his toe on the way through.

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