Paleontologist Stephen Jay Gould, in his book Wonderful Life: The Burgess Shale and the Nature of History (1989), introduced a broad swath of the reading public to the concept of historical contingency. In the book, he explores how the world of living organisms could move from the many "weird" forms of Cambrian life (at a juncture some 530 million years ago) fossilized in the Burgess Shale, to creatures such as us. He states that there are no natural laws requiring a particular outcome (e.g., us), rather, he posits, what's at work, and what shaped our world, is historical contingency which is:
an unpredictable sequence of antecedent states, where any major change in any step of the sequence would have altered the final result. The final result is therefore dependent, or contingent, upon everything that came before - the unerasable and determining signature of history. (Wonderful Life, p. 283)
When considering the final product of such a process, apparently luck, or chance, plays a determinative role. The previous post on this blog (the one about watches, God, and evolution) draws on some different work by Gould to posit that evolution through natural selection, not some divine force, shaped the biological world around us. What role has chance played in life, what's the connection between chance and evolution, and what does historical contingency have to say about that connection? I address those questions in this post through a review of a book which I read only by chance or, more precisely, by mistake.
In that earlier post, I reference Sean Carroll's book The Big Picture: On the Origins of Life, Meaning, and the Universe Itself (2016) when asserting that the human eye came into being through natural selection. Afterwards I went in search of other works by Carroll, and came upon the thoroughly enjoyable A Series of Fortunate Events: Chance and the Making of the Planet, Life, and You (2020) The title is a nice play on Lemony Snicket's series of books titled A Series of Unfortunate Events. Wait, I will forestall a rise in your blood pressure, by hastening to admit that it took me an embarrassingly long time to realize that the Sean Carroll whose book I mention in that previous post is a physicist and is NOT the author of A Series of Fortunate Events who is biologist Sean B. Carroll. A whole different kettle of fish. Fittingly, had I not made that error, I might never have read A Series of Fortunate Events, at least not when I did, which would have been an unfortunate event.
The biologist Carroll's A Series of Fortunate Events is a brief, graceful, and often funny read about the central role chance has played, and plays, in determining how the world and everything in it - organic and not - has come to be. Carroll structures his exploration of chance around its role in two broad realms: the "inanimate" (read cosmological and geological), and the "animate" (read biological). There are two components to the biological realm: a part embracing life in general where evolution through natural selection as well as mutation are at work, and a part focused on the way chance affects how each of us individually is conceived, lives, and dies. Quite ambitious and he pulls it off with surprising ease.
I think it useful at the outset to draw attention to the two pages that mark the transition from Carroll's discussion of the inanimate to that addressing the animate. In them, he explains what he means by chance: "a rare, unpredictable, or random event, or one that entails so many variables or forces that is near enough to be random," (p. 59) And, perhaps even more important, he defines the concept of historical contingency: "a past event or process that was necessary for a particular outcome." (p. 59) He captures the significance of the relationship between the two when he writes:
Chance here, then, pertains to an event itself, while a contingency emerges through the benefit of hindsight. The interrelationship between the two is that a chance event can become a historical contingency through its effects. Contingency is the aftermath of chance. (p. 59-60)
Carroll presents various examples of chance in the broad realms around which the book is structured. I mention a few of the most prominent. The star of the inanimate realm is cosmological in nature: the asteroid that smashed into the Yucatan Peninsula 66 million years ago, dooming the non-avian dinosaurs and myriad other species of animals and plants. This asteroid was a great big ball of chance. As Carroll point out, a mere 30 minutes was key. Had the asteroid hit Earth that many minutes earlier or later, it would have landed in deep ocean waters and likely not played havoc with the world. Instead, the bolide landed on a part of the planet that magnified its most lethal effects. And, so, the asteroid "hit the reset button" for life on Earth.
Regarding chance in the biological realm for life in general, Carroll focuses on a biologist about whom I knew nothing - Jacques Monod whose work included exploring how genes control enzyme production. He shared the 1965 Nobel Prize in Physiology or Medicine. With the publication of his book Chance and Necessity in 1970, Monod achieved an unexpected degree of fame and notoriety. Carroll asserts that, when Monod wrote about how mutations appeared in DNA, "he delivered one of the most powerful ideas in five centuries of science." (A Series of Fortunate Events, p. 8) Monod stated that
chance alone is at the source of every innovation of all creation in the biosphere.
Pure chance, absolutely free but blind, at the very root of the stupendous edifice of evolution: this central concept of modern biology is no longer one among other possible or even conceivable hypotheses. It is today the sole conceivable hypothesis, the only one that squares with observed and tested fact." (Text is from Chance and Necessity as quoted in A Series of Fortunate Events, p. 8)
Amazing. Carroll is equating in importance Monod's claim about chance with, say, Darwin's theory of evolution through natural selection. In fact, the two go hand in hand. Without the possibility of change in living organisms, there would be no variation for natural selection to work with. That the variation occurs and is random speaks to the role of chance. Darwin, Carroll says, had no knowledge of the actual process that generated variations, but characterized them as "accidents."
Carroll devotes a couple of chapters to mistakes or mutations that can occur in the genome, showing that they are random, a matter of chance in how the genetic code might be altered. The key is that the four bases that constitute the alphabet of which DNA is composed exist in two alternate forms and can shift from one to the other. If, during copying, the rarer form of a base is present, it will bond with the "wrong complementary base," yielding a mutation. Carroll labels the shifting between forms as "quantum fibrillation," a feature inherent in the bases, meaning: "Mutation, then, is a feature, not a bug in DNA." (p. 95) He sums up the interplay between mutation (the product of chance) and natural selection: "Chance invents, and natural selection propagates the invention." (p. 118) But propagation may occur only if the mutation offers an organism some advantage in the struggle for survival.
As for the role of chance in my life or yours, Carroll starts with our conception. It's not just how, out of some 100 million of a male's sperm streaming toward the female's egg, only one will fertilize it. More impressive is that, based on any male and female's chromosomes, there are some 70 trillion different, genetically unique children that a couple might create in that moment, but only one is. (p. 131) Other aspects of chance playing out in our lives that Carroll explores include some unfortunate events, among them having cancer.
He nicely sums up what I believe are the overall takeaways from the book:
I have shown how we know that we are all here, both collectively and individually, through a series of accidents – cosmological, geological, and biological accidents. I have also shown how and why some of us will depart via accident.
Our chance-driven world is a profound revelation. It is astonishing that blind chance is the source of all novelty, diversity, and beauty in the biosphere. I hope that you are wonderstruck at what an asteroid, sliding tectonic plates, and a fibrillating polymer of just four bases have wrought. (p. 164-5)
As much as I liked the book, I do have a couple of quibbles. First, contingency is at the heart of Carroll's assertion that we, and all life around us, is here by virtue of chance. It's the sequences of chance (i.e., "rare, unpredictable, or random") events in the histories of all taxa that create the contingencies necessary for the very existence of all types of organisms. The longer that sequence, I would suggest, the more unlikely the ultimate outcome. Since this is his argument, I find it curious, to say the least, that Gould doesn't appear in the index (and I don't think I encountered his name in the text) of A Series of Fortunate Events, and that there's no entry for Wonderful Life or anything else by Gould in Carroll's bibliography. That's a shame because Gould's analysis of historical contingency is exactly on point and, indeed, the metaphor he used to capture its essence is stellar. Gould asked, what we'd end up with if "we rewound life's tape to a distant past." (p. 308, emphasis added) His answer and, clearly Carroll's as well, is that, replaying the tape would lead to a planetary biota quite different from today's and one that almost certainly would not include anything closely resembling us.
A second quibble which speaks to the rewinding and replaying of life's tape. I think Carroll should have dealt with the implications for chance of convergent evolution, the process through which the same features arise independently in different taxa. I'm not prepared to treat it here, other than to note that it suggests that some paths that evolution might take may be more likely than others, regardless of the starting point. There may, in fact, be guardrails for the development of life, so, maybe, not anything goes. [Later edit: I discovered several weeks after writing this post that I'd already written about convergent evolution and its import for Gould's thought experiment of rerunning the tape. It was in a post reviewing Jonathan Losos excellent book Improbable Destinies back in 2017. Losos came down on Gould's side with caveats.]
That said, I have to salute the wonderful outcome of having misidentified the author.
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