I have been an avid reader and interested in astronomy/space ever since I could remember. I remember really loving Stephen Hawking and his documentaries on black holes. I would read anything I could find on constellations and stars. From there I went on to reading sci-fi. I then recall seeing The Martian Chronicles by Ray Bradbury and from then on I had become interested in sci-fi writing. But, as I grew older, I drifted away from sci-fi and now only read non-fiction. Then when I got older I got into ‘HBD’ (chronicled here) and along with it evolution—but, unlike other ‘HBDers’ I became enamored with the work of Gould, while some of my favorite books come from him. Gould wrote a lot about evolutionary contingency—the degree to which an outcome could be different. Evolutionary contingency is a big topic in philosophy of biology, and Bradbury has a great short story on this type of contingency.
Ray Bradbury is an interesting author—one who has many short stories and regular books. One of my favorite stories from Bradbury is one called A Sound of Thunder which chronicled a time machine company who let people go back in time to hunt any animal they’d like—if you want to take down the ancestor of a whale before it became aquatic, just name the place and they will send you there. They were told to only stay on the path laid out by the time machine company—animals they could shoot were marked with red paint, presumably those animals would have died anyway so killing them would not change any outcomes. The text from Bradbury is worth quoting in full, as it wonderfully captures the thought of evolutionary contingency:
He indicated a metal path that struck off into green wilderness, over streaming swamp, among giant ferns and palms. “And that,” he said, “is the Path, laid by Time Safari for your use, It floats six inches above the earth. Doesn’t touch so much as one grass blade, flower, or tree. It’s an anti-gravity metal. Its purpose is to keep you from touching this world of the past in any way. Stay on the Path. Don’t go off it. I repeat. Don’t go off. For any reason! If you fall off, there’s a penalty. And don’t shoot any animal we don’t okay.”
“Why?” asked Eckels.
They sat in the ancient wilderness. Far birds’ cries blew on a wind, and the smell of tar and an old salt sea, moist grasses, and flowers the color of blood.
“We don’t want to change the Future. We don’t belong here in the Past. The government doesn’t like us here. We have to pay big graft to keep our franchise. A Time Machine is finicky business. Not knowing it, we might kill an important animal, a small bird, a roach, a flower even, thus destroying an important link in a growing species.”
“That’s not clear,” said Eckels.
“All right,” Travis continued, “say we accidentally kill one mouse here. That means all the future families of this one particular mouse are destroyed, right?”
“And all the families of the families of the families of that one mouse! With a stamp of your foot, you annihilate first one, then a dozen, then a thousand, a million, a billion possible mice!”
“So they’re dead,” said Eckels. “So what?”
“So what?” Travis snorted quietly. “Well, what about the foxes that’ll need those mice to survive? For want of ten mice, a fox dies. For want of ten foxes a lion starves. For want of a lion, all manner of insects, vultures, infinite billions of life forms are thrown into chaos and destruction. Eventually it all boils down to this: fifty-nine million years later, a caveman, one of a dozen on the entire world, goes hunting wild boar or saber-toothed tiger for food. But you, friend, have stepped on all the tigers in that region. By stepping on one single mouse. So the caveman starves. And the caveman, please note, is not just any expendable man, no! He is an entire future nation. From his loins would have sprung ten sons. From their loins one hundred sons, and thus onward to a civilization. Destroy this one man, and you destroy a race, a people, an entire history of life. It is comparable to slaying some of Adam’s grandchildren. The stomp of your foot, on one mouse, could start an earthquake, the effects of which could shake our earth and destinies down through Time, to their very foundations. With the death of that one caveman, a billion others yet unborn are throttled in the womb. Perhaps Rome never rises on its seven hills. Perhaps Europe is forever a dark forest, and only Asia waxes healthy and teeming. Step on a mouse and you crush the Pyramids. Step on a mouse and you leave your print, like a Grand Canyon, across Eternity. Queen Elizabeth might never be born, Washington might not cross the Delaware, there might never be a United States at all. So be careful. Stay on the Path. Never step off!”
“I see,” said Eckels. “Then it wouldn’t pay for us even to touch the grass?”
“Correct. Crushing certain plants could add up infinitesimally. A little error here would multiply in sixty million years, all out of proportion. Of course maybe our theory is wrong. Maybe Time can’t be changed by us. Or maybe it can be changed only in little subtle ways. A dead mouse here makes an insect imbalance there, a population disproportion later, a bad harvest further on, a depression, mass starvation, and finally, a change in social temperament in far-flung countries. Something much more subtle, like that. Perhaps only a soft breath, a whisper, a hair, pollen on the air, such a slight, slight change that unless you looked close you wouldn’t see it. Who knows? Who really can say he knows? We don’t know. We’re guessing. But until we do know for certain whether our messing around in Time can make a big roar or a little rustle in history, we’re being careful. This Machine, this Path, your clothing and bodies, were sterilized, as you know, before the journey. We wear these oxygen helmets so we can’t introduce our bacteria into an ancient atmosphere.”
This passage from Bradbury wonderfully illustrates evolutionary—historical—contingency. Things could have been different—this is the basis of the contingency argument. The universe does not repeat itself—if we were to replay the tape of life we would get a completely different outcome—Lane (2015) states maybe octopi would rule the earth? We could replay the tape of life, have it go exactly as it did to lead up to today, change ONE SEEMINGLY MINISCULE THING (say, stepping on a bug that did not die) which would then cascade throughout history leading to a change in the future. Evolution is full of passive trends, with no indication that—for example with body plans—that there is a drive to become more complex—it is passive (Gould, 1996: 207):
All the tests provide evidence for a passive trend and no drive to complexity. McShea found twenty-four cases of significant increases or decreases in comparing the range of modern descendants with an ancestor (out of a potential sample of ninety comparisons, or five groups of mammals, each with six variables measured in each of three ways; for the other comparison, average descendants did not differ significantly from ancestors). Interestingly, thirteen of these significant changes led to decreases in complexity, while only nine showed an increase. (The difference between thirteen and nine is not statistically significant, but I am wryly amused, given all traditional expectation in the other direction, that more comparisons show increasing rather than decreasing complexity.
Gould first put forth his contingency argument in Wonderful Life—any replay would be different then the next. Gould critiqued the increasing complexity claim, arguing that diversification is always accompanied by decimation—once a mass extinction (say, an asteroid impact) occurs, there will then be subsequent diversification after the decimation.
We have no idea why certain organisms persisted over others after periods of decimation—and ‘adaptation’ to environments cannot be the whole story. Out of all of Gould’s writing that I have read in my life, this passage is one of my favorites as it perfectly captures the problem at hand:
Wind the tape of life back to Burgess times, and let it play again. If Pikaia does not survive in the replay, we are wiped out of future history—all of us, from shark to robin to orangutan. And I don’t think that any handicapper, given Burgess evidence as known today, would have granted very favorable odds for the persistence of Pikaia.
And so, if you wish to ask the question of the ages—why do humans exist?—a major part of the answer, touching those aspects of the issue that science can treat at all, must be: because Pikaia survived the Burgess decimation. This response does not cite a single law of nature; it embodies no statement about predictable evolutionary pathways, no calculation of probabilities based on general rules of anatomy or ecology. The survival of Pikaia was a contingency of “just history.” I do not think that any “higher” answer can be given, and I cannot imagine that any resolution could be more fascinating. We are the offspring of history, and must establish our own paths in this most diverse and interesting of conceivable universes—one indifferent to our suffering, and therefore offering us maximal freedom to thrive, or to fail, in our own chosen way. (Gould, 1989: 323)
Contingency is about counterfactuals—what could have happened, what could have been, or what would have been had some certain condition changed, with everything before that occurring as usual. Bradbury’s A Sound of Thunder wonderfully illustrates the contingency of the evolutionary process—change one seemingly small, minuscule thing in the past and this could snowball and cascade to huge changes in the future—we may never have existed or we would have existed but have been radically different. If we could go back in time and, say, crush a butterfly and see the changes it would have made, we could say that the event that caused the future to change was the crushing of that butterfly—this could have, eventually, led to the non-existence of a certain group of people or a certain group of animals which would have radically changed the outcome of the world—both the natural and human world.
So, if we could replay life’s tape from the very beginning, I do believe that life as we know it would be different—for if we played it from the beginning, we could have a scenario as described by Bradbury—everything could go exactly the same with one small seemingly minuscule change snowballing into a world that we would barely recognize.
I believe the many cases of convergent evolution indicate that if earth “started over” we’d still see a lot of the same adaptations we do now.
Thank you, high praise coming from you my friend.
While I do agree that what we term “adaptations” would arise again, or even similar ones, I don’t think that that would mean that if we replayed life’s tape that we would get the same outcome.
What do you think?
No I agree that the world would look different. I just think there would still be organisms that could fly, swim, run on four legs, etc.
Let’s say something happens like Bradbury describes: Would we get the same outcome or will we see an unrecognizable world?
Oh, no doubt about that. There are only so many ways an organism can move, no?
Well not just that. But environment isn’t as variable as some think. At least when it comes to the inanimate aspects. That’s why usually the most unique and specialized adaptations tend to come from warmer climates. Not just movement, but I’d also assume things like gills, lungs, body plans, and even some physiological systems. I mean so many organisms have a nervous system or similar that it’s a true testament to its adaptive “power”.
There we go
Highly relevant video you might find interesting RR