It is the year 2092. Nemo Nobody is the last mortal on our planet. At 117 years old, the brittle Nemo is almost at the end of his life. Everyone around him will live forever, whereas he will be the last one to die. Nemo spends his last days in a hospital where he features in a reality show and is interviewed by a journalist every day. But the journalist finds reconstructing Nemo’s past difficult, as many of his memories seem to contradict one another. For example, when his parents got separated, Nemo either had to stay with his father in England, or move to the United States with his mother. But Nemo never really made that choice. He remembers both living with his mother and taking care of his sick father. Later he remembers being married to three different wives, in varying degrees of happiness. It is as if Nemo never makes a decision. When he is confronted with a fork in the road, he walks both paths. Looking back at his life it as if he is peering through a kaleidoscope – seeing all the possible lives he could have lived at once.
The movie Mr. Nobody raises some mind-boggling questions about choice and consequence. How many different lives could you have lead? What if your parents had moved to a different town when you were young? What if you had studied medicine, instead of psychology? What if you had missed that bus and never met your current partner? Change just a few critical details of your personal history, and you would end up leading a different life altogether. You are where you are know, because a long chain of improbable events brought you there. This dependency on the past is called contingency. Sometimes the dependency is obvious. If you choose not to attend high school, you cannot attend college for example. Other dependencies, such as the launch of your company after bumping into your future business partner at the airport 5 years ago, seem insignificant at first, but can cause a cascade of consequences later on.
But not everything that happens in our life is the result of contingency. I don’t often say this – but some things are ‘destined to happen’. I am not talking about finding Mr. Perfect or Mrs. Right. I am referring to a different kind of destiny. A destiny that is shaped by our biology or environment, for example. A caterpillar in a cocoon will always emerge as a butterfly, not as a bumblebee or as a beetle. Whatever happened in its life as a caterpillar, this particular outcome cannot be changed. Similarly, someone born with one faulty copy of the haemoglobin gene will develop sickle cell anaemia. And whichever life I would have lived, I’d probably be great at growing a beard. Some tendencies are inevitable.
There is a tension between these two forces. Contingency is a random process. Yes – the future depends on the past, that past is full of ‘historical accidents’. All possible outcomes are rooted in random events. Inevitabilities, on the other hand, are non-random. They have a direction and impose limits on what is possible and what is not. This tension between random and non-random not only affects the course of our own lives, but also that of evolution itself. As a historical process, evolution should be subject to contingency. But we also know that evolution follows certain rules and laws – like natural selection. So how do these two forces play out in nature? To what extent is evolution random? This might look like a simple question, but it has divided some biologists deeply.
One of the most passionate advocates for a contingent view of evolution was Stephen Jay Gould. In his book Wonderful Life he describes a famous thought experiment, where he imagines what would have happened if the asteroid that struck the earth 65 million years ago had missed it instead. The asteroid impact lead to the extinction of thousands of plants and animals, including all large dinosaurs. If the asteroid had flown by our planet, dinosaurs could have continued their rule over the earth. Mammals would never have flourished like they did after the original catastrophe. Perhaps they would have remained small and nocturnal creatures, destined to scrape by in a reptilian world. Gould thinks it is unlikely that humans, or human-like intelligence, would ever evolve in this alternate reality.
Devastating asteroids are historical events that are not part of any theory of evolution. Still such events have the power to change evolution’s course. Even the simplest mutation in a gene is historical event, because they are unpredictable and not predetermined. While biologists may now know some of the laws and forces that drive evolution, historical contingency prevents them from predicting its future. A biologist studying sauropods (‘long-neck dinosaurs’) 66 million years ago could never suspect that these successful, lumbering giants would become extinct one million years later for example. Just a small change in life’s history is enough change the world into one that is very different from the one we see today. Gould said this best himself:
We came this close (put your thumb about a millimetre away from your index finger), thousands and thousands of times, to erasure by the veering of history down another sensible channel. Replay the tape of evolution a million times from a Burgess beginning, and I doubt that anything like Homo Sapiens would ever evolve again. It is, indeed, a wonderful life.
~Stephen Jay Gould, Wonderful Life
The Burgess Shale that Gould mentions is a fossil bed from the Cambrian and forms the main inspiration for Gould’s argument. The creatures in the Burgess Shale were buried in an undersea mudslide around 500 million years ago. This sudden burial lead to the perfect preservation of these animals – even their soft tissues are immortalized in the rocks. The palaeontologists Simon Conway Morris, David Briggs and Harry Whittington reanalyzed and reconstructed many of the Cambrian fossils of the Burgess Shale. They found that many of the Burgess animals had bizarre designs. Animals like Opabinia, Aysheaia and Hallucigenia al have body plans that are so unfamiliar that they appear to be unrelated to animals of today. Even the not-too-spectacular Marrella doesn’t fit into any modern group. Marella has similarities to crustaceans and trilobites, but belongs to neither family.
Although they turned to stone a long time ago, these strange Burgess creatures still pose a burning question: why did they go extinct? Why can’t we buy a pet Opabinia in our pet stores? I’m sure aquarium hobbyists would love to get there hands on Opabinia – it would add some unique diversity to their aquariums, for the millions different species that are alive today only represent a handful of different body plans. A million different beetles are still a million variations on a common theme. From the ~20 different Cambrian arthropod designs present in the Burgess Shale, only four survived. Why only these four, and not another set? Gould thinks that it was sheer luck. We can’t really say why some species went extinct, he says. Their bauplan wasn’t ‘less adapted’ or ‘more primitive’ than that of their more lucky relatives. They were just different. It’s as if their fate was decided in a cruel lottery. But if you would pick a different set of lucky survivors, and marrelloids instead of crustaceans would have crawled around the floors of the sea. A small change in Cambrian times, but a radically different outcome.
Gould’s interpretation of the Burgess Shale is not uncontroversial. Two of the heroes in Gould’s book, David Briggs and Simon Conway Morris, criticized the theories of their admirer. David Briggs published a couple of papers that aimed to show that the Burgess creatures weren’t that morphologically diverse at all. But it was Conway Morris who challenged Gould’s claims on contingency in his book the Crucible of Creation.
When Simon Conway Morris looks back at the history of life, he doesn’t see randomness and contingency. He sees direction and convergence. Convergence is the observation that evolution tends to come up with similar answers when it is faced with similar problems. All animal lineages evolved eyes, for example. From the compound eyes of insects to the lens-bearing eyes of squids and vertebrates, each animal has found its own way to see the world around it. The form of the eye might vary, but having eyes seems to be a good rule of design. According to Conway Morris, evolution converges on a limited set of solutions time and time again.
Similar environmental selection pressures, acting on differing anatomies, can create convergent or parallel adaptations. [..] History is constrained, and not all things are possible. To understand how creatures that are descended from very different groups can evolve similar forms and functions, consider that dolphins, which evolved from doglike mammals, are shaped like fish because there exists an optimal shape for moving through water—a classic example of convergent evolution.
~Simon Conway Morris, “Showdown on the Burgess Shale,” Natural History magazine, 107 (10): 48-55.
There are only so many ways of moving around in water so dolphins are restricted in their options. Conway Morris doesn’t say that the specific from of a dolphin is inevitable. There are numerous differences between fish, ichtyosaurs and dolphins. Fish have gills, whereas dolphins breathe through a blowhole. Yet it is obvious that all these different creatures are shaped like a fish. Maybe ‘the form of the fish’ is the only logical endpoint for marine creatures with a spine. He argues that replaying the tape of life will give us a different, but very similar outcome. Yes – Marella could certainly have become the ancestor of a successful lineage of marine arthropods. But they would have filled the same niches as trilobites or crustaceans.
So where do we go from these two conflicting views? Is evolution guided by contingency, or convergence? It is important to remember that this is not an ‘either-or’ issue at all. Contingency and convergence are not mutually incompatible. It would be silly to say that evolution is free of constraints or predictable patterns. It would be equally silly to say that history plays no role in evolution. Contingency and convergence both shape the possibilities and impossibilities of evolution. Figuring how these forces are together weave the tapestry of evolution should be an exciting enterprise (and provide enough fuel for another blogpost).
Why then, do these questions incite so much debate? This is because deep down, they are not about dolphins and Opabinia. The question all of us want to find an answer for is whether the evolution of human conciousness was somehow inevitable. Many, including Conway Morris, think it was. I most recently came across this view in Kevin Kelly’s latest book, What Technology Wants. In this book, technology enthusiast Kevin Kelly goes as far as reversing Gould’s statement that ‘humans are an entity, not a tendency’ into the exact opposite statement ‘humans are a tendency, not an entity’. Convergence, Kelly says, drives life to become more complex and yes, more conscious. Twelve years ago, Gould already pointed out the weak point in this argument:
Evidence for convergence requires multiple cases of independent evolution, while the example that we all carry closest to our hearts (and that engenders the emotional oomph in this debate)—the evolution of consciousness in Homo sapiens—remains an outstanding singleton in the only history of life we know: the story of our own planet.
~Stephen Jay Gould, “Showdown on the Burgess Shale,” Natural History magazine, 107 (10): 48-55.
I have to agree with Gould here. In contrast to the repeated evolution of fishlike creatures, we have only know one example of a conscious creature evolving. It is impossible to claim that the evolution of consciousness is a something that has occurred repeatedly in the history of life. We should be open to the idea that we are here partly because of the inevitabilities that constrain evolution, and partly because we have been lucky enough that history unfolded as it did.
Many find this idea that mankind is not the inevitable outcome of evolution offensive. It rubs against our collective, human pride. Copernicus, Galileo and Kepler already showed us that earth is not in the centre of the universe. Darwin removed mankind from the centre of creation. The last retreat of our feeling of human superiority seems to be the thought that somehow, everything is meant to be this way. It is comforting to believe that the evolution of human consciousness is the fulfilment of a promise made 4,6 billion years ago. Because what would we be left with, if mankind turned out to be a fortunate accident?
I think we would be left with an even greater appreciation of the wonderful world in which we live. The unlikeliness of a conscious species arising to start talking and reflecting on its own place in this universe, doesn’t make evolution any less stunning or interesting. It makes it more so. Nemo Nobody said this better than me. When the journalist asks Nemo which of his conflicting memories represent the ‘right’ story of his life, he replies “Each of these lives is the right one. Every path is the right path. Everything could have been everything else and it would have had just as much meaning.”
Butterfly photograph by Patrick Ronan.
Opabinia illustration found here, artist unknown. Please contact me if you are (or know) the original artist.
Ana and her pet Opabinia illustration by Glendon Mellow. Check out his site here.
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