Depicting Non-Progressive Evolution

While working on the rhizomatic animism post the other day, I kept thinking about the old cliche that a picture is worth a thousand words. Tim Ingold’s use of simple line drawings to depict different ways of perceiving life (or being in the world) is incredibly powerful. His diagrams also reminded me of an earlier post in which I commented on the non-progressive nature of evolution. That post prompted some spirited discussion from some of my best internet friends. I now want to follow up on that discussion with some more depictions.

Let’s start with this famous diagram, the tree of life, by German naturalist Ernst Haeckel:

When the history of life is depicted in this way, it sends the unmistakable message that evolution is progressive: it begins at the base or root with single-celled organisms and over evolutionary time it grows. At the apex or crown is magnificent man, the implied telos or outcome of all this evolution. It’s a tidy progressive portrait: simplicity at the bottom, complexity at the top.

Thanks to the genius of Carl Woese, we no longer represent the history of life in this way. Instead we depict organisms as being rooted in a primordial last common ancestor that has given rise to all existing life forms on earth today:

As I noted earlier, an anthropocentric perspective which places humans at the center of everything creates the illusion that evolution is progressive or directed toward some goal. It isn’t. Life began on earth some 3 billion years ago and after 3 billion years of evolution, the vast majority of life forms remains simple. We live in a (simple) microbial world, not a (complex) intelligent one.

If microbes could write evolutionary history, things would look much different. In the absence of such a history the next best thing is Stephen Jay Gould’s Full House (1997), which shatters the illusion that evolution is progressive. The greatest frequency or mode of life on earth, in terms of biomass and diversity, is microbial. It remains firmly against the left wall of minimal complexity, close to where it began.

My observation prompted Tom Rees to comment: “The graph does show that evolution is directional. Complex brains have to build on less complex brains.” Because I didn’t explain the graph very well, I responded to Tom by noting that directional evolution is in the eye of the human (or primate or mammal) beholder. The mode of life — its greatest frequency, biomass, and diversity — is up against (or near) the left wall of non-complexity. It started there, and after evolving for over 3 billion years, it has remained there. This doesn’t look very directional.

Toward the left side of non-complexity and non-intelligence, we have microbes and, moving toward the right, we have insects. In terms of numbers, species, biomass, and diversity, these are the dominant forms of life on earth. These forms are still evolving, but they aren’t evolving towards complexity or intelligence.

Our multicellular prejudice — our love for big things that we can easily observe — causes us to focus on the right side of complexity and intelligence, and then claim that these relatively few and non-diverse species indicate evolution is directional. I don’t see how we can justify this argument.

Isolating a single and uncommon strand of evolution, such as the right tail of complexity or intelligence, doesn’t make evolution directional to the right. The fact remains that the isolated right tail of evolution is dwarfed by the diversity and mass of life to the left, which is non-complex and non-intelligent. This mass of life to the left has not been static either; it too has evolved — it just hasn’t evolved towards complexity or intelligence.

I’m not sure what the rationale or argument would be for mono-focusing on the right tail, which is an evolutionary outlier, and not considering everything to the left. If we look at the whole or entire picture of evolutionary life, it is non-directional. If evolution were directional, then all forms of life would show movement toward the right or towards multi-cellularity, complexity, sentience, and intelligence. That hasn’t happened and isn’t happening. Microbes, insects, and fish completely dominate life on earth and none of them are moving in this direction or progressively evolving towards complexity.

This exchange prompted Alex Fairchild to chime in with this bit of brilliance:

“When I try to explain this concept, I attempt to describe the tree of life as being contained within a sphere, with the center being the LCA (“last common ancestor”) of life, and the surface being the present, and each branch tip being a species. The surface of the sphere is vast, with billions of species, each just as old as the other. Only by picking one (the human branch), and looking back down the tree, do you see a directionality towards intelligence. Picking a random branch will land you on a one celled organism, with near certainty.”

This is a fantastic way of word-visualizing the evolutionary history of life on earth from past to present. Until recently I was not able to find any good images depicting his words. I now have two, both of which were created for other reasons. I really like this first one because we can imagine the small starting dot as the last common ancestor, and the expansion as the evolving history of all life during the past 3 billion years — the end points are the present:

Humans, of course, are just a single strand at the very end of one of these lines. Here is a static view, with humans being just a single point at the end of a single strand:

The only deficiency in this depiction is that there are millions of (mostly microbial) living species on earth, so we need millions of lines and points at the outer fringes (or present). Our diagrams obviously can’t do this, but we can imagine it. We can also imagine humans being just one of those million points.

For those who don’t have time to read Gould’s book Full House, this article provides a concise overview of the argument, and this excerpt indicates its tenor:

Sigmund Freud often remarked that great revolutions in the history of science have but one common, and ironic, feature: they knock human arrogance off one pedestal after another of our previous conviction about our own self-importance. In Freud’s three examples, Copernicus moved our home from center to periphery, Darwin then relegated us to “descent from an animal world”; and, finally (in one of the least modest statements of intellectual history), Freud himself discovered the unconscious and exploded the myth of a fully rational mind.

In this wise and crucial sense, the Darwinian revolution remains woefully incomplete because, even though thinking humanity accepts the fact of evolution, most of us are still unwilling to abandon the comforting view that evolution means (or at least embodies a central principle of) progress defined to render the appearance of something like human consciousness either virtually inevitable or at least predictable.

The pedestal is not smashed until we abandon progress or complexification as a central principle and come to entertain the strong possibility that H. sapiens is but a tiny, late-arising twig on life’s enormously arborescent bush – a small bud that would almost surely not appear a second time if we could replant the bush from seed and let it grow again.


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14 thoughts on “Depicting Non-Progressive Evolution

  1. Chris Tolworthy

    “I’m not sure what the rationale or argument would be for mono-focusing on the right tail, which is an evolutionary outlier, and not considering everything to the left. If we look at the whole or entire picture of evolutionary life, it is non-directional.”

    One rationale is that everything ultimately averages to zero, so considering the middle tells us literally nothing. Only the differences from the mean give a thing its identity. If the shape of the graph is normal distribution then the standard deviation has in fact increased, even if only by a hair’s breadth.

    Another rationale is that the extremes exert disproportionate influence: our brains pay great attention to extreme values for good reason. Take temperature for example. Almost all temperatures an organism may experience are huddled around a mean. But a single spike means the organism is dead. Humans could be that spike for the evolutionary tree, if we mess up badly enough (or we could save the planet from cosmic extinction: we matter).

    Evolution is like numbers. Numbers do not progress. They do not change. For every large number there is an infinite number of smaller numbers that make it up, and all numbers average to zero. Yet for most purposes it help to think of numbers as having a direction, and of bigger numbers being somehow more important than small ones.

    At least, that’s how I see it.

  2. Cris Post author

    But we aren’t considering the middle or mean of a curve that encompasses all forms of life. We are considering its statistical mode, which is overwhelmingly simple and non-complex. If we look at all life forms and don’t just focus on vertebrates-mammals-primates-humans, the distribution shows a strong (left) skew.

  3. Alex Fairchild

    My first citation! I am unbelievably proud of myself right now – and very excited that you grok my ‘sphere of life’ notion. I think I should make an animation that visualizes the concept… though don’t expect a quick turnaround, it’s been decades since I did any 3d animation. But you’ve given me a shot in the arm!

  4. Cris Post author

    A well-deserved citation! Your words resonated inside my head and I used them while teaching my last class — my chalkboard diagram, however, was woefully insufficient. You absolutely should do a sphere of life animation — this is really important stuff and we need something better than what I’ve found. Let me know when you’ve got something. Perhaps we should write an article to accompany the animation.

  5. J. A. Le Fevre

    Recognize that plants are primary producers, that millions of microbes serve to condition the soil (or environment as a similar process goes on under water as well) for the benefits of a single plant, hundreds to thousands of plants per animal on to all higher life forms and one could use that same data to justify the opposite conclusion or even design: The simple are maintained to enable and support the ‘goal’ of complex development. In other words, were evolution directed, the results would be exactly what you presented.

  6. Cris Post author

    Microbes don’t do any of these things “for the benefit of plants” and microbes do not go about their business “to enable and support” any goals. In fact, the majority of microbes don’t exist in soil and thus don’t exist for the benefit or purpose of plants.

    Your suggestion is akin to saying that the plants and animals we eat exist for the benefit of humans, and evolved to support humans. I don’t associate predation and parasitism with any goals other than survival. There is nothing teleological (or ennobling) about trophic escalations.

    Your observations (which are more like predilections) are precisely the kind of a priori and anthropocentric perspective that these data do not support. Goals, directions, and designs exist in the minds of humans, not in the rest of the living world.

  7. J. A. Le Fevre

    Yes and no, the data is simply ambiguous – it proves nothing. The condition of humans exist requires the distribution of complexity you present. The simple fact of human existence dictates the distribution. If you assume random, the result is the same as if you assume directed – the data ‘supports’ alternate conclusions with alternate starting assumptions.

  8. Cris Post author

    The whole methodological point of this exercise is to consider the entire distribution, which is not a bell curve and is tremendously skewed (towards the left, which is simplicity). From a statistical perspective (and considering all rather than just some of the data), this kind of (non-normal) distribution doesn’t justify a conclusion or trend of directionality toward the outlier right tail (which is complexity). From a quantitative perspective, this is not ambiguous.

    The only way this can be be ambiguous, or explained away, is from a qualitative perspective. Is that your preference?

  9. J. A. LeFevre

    I want to highlight a basic flaw in the foundational assumption of your argument. There is a simple proof circulating in High Schools to show that 1 = 2. One step of this proof involves division by zero, a forbidden operation. The flaw of this argument is the assumption that if evolution was progressive, that all simple life would be (somewhat uniformly) evolving to be more complex. Like division by zero, that too appears forbidden – complex life forms are dependant upon the simple ones to survive, and many niches in the environment can only (yet in this world to date) be exploited by microbes.
    Nature does not appear to abandon niches, so microbes will continue to stay microbes in those niches until kicked out by a more competitive complex organism. But that is not what we typically see – Take the termite: a complex life form that has created an internal environment for cellulose digesting bacteria. Complex life forms are not displacing simple ones, they are harboring them, promoting their survival. The success of complex life forms guarantees the proliferation of far greater quantities of simple ones. Most of the DNA in your body is not human, but of the symbiotic microbes you harbor (supposedly they are a lot smaller than your cells, so you can fit more of them into a smaller space – I haven’t confirmed this, it may be myth!).
    Nature appears to be evolving complexity as fast as it can, but the simple life is brought along for the ride. The curve is skewed towards simple because (in part) complex life depends upon it. Its not about ‘what’s better’ (qualitative), but what works.

  10. Cris Post author

    I’m not sure what you are arguing. I don’t assume that evolution is progressive; therefore I don’t assume that all simple life would be evolving toward complexity. I also don’t see how a forbidden math operation has anything to do with the history or evolution of life. I also fail to see how the dependence of complex organisms on simpler organisms suggests directional or progressive evolution. This fact simply establishes a relationship between organisms, not directionality in evolution.

    Here is a fact to chew on: all complex organisms could go extinct today, and (microbial) life on earth would go on much as it always has, relatively unaffected. The (statistical) mode of life would remain unchanged. But if all microbial organisms went extinct today, all complex organisms would go extinct shortly thereafter. We live in a microbial world, not a multi-cellular world.

    I recommend that you read Lynn Margulis’ “Microcosmos” and Gould’s “Full House” and then get back to me on these subjects.

  11. J. A. LeFevre

    Yes, that is my point, my whole argument: ‘…simply establishes a relationship between organisms, not directionality in evolution.’
    Gould and you are arguing that it ‘shatters the illusion that evolution is progressive.’ It does no such thing, it simply establishes a relationship between organisms, not directionality (or non-directionality) in evolution.

  12. Wearily wearily

    “I’m not sure what you are arguing. I don’t assume that evolution is progressive; therefore I don’t assume that all simple life would be evolving toward complexity.”

    His point was that opponents of progressive evolution often point out the great mass of simple life that does not seem to be moving toward greater complexity, but that even assuming progressive evolution is occurring, there is no reason to think that ALL simple life forms would be evolving toward greater complexity uniformly (for the reasons he listed above). It’s a valid point, IMO.

    Maybe I’m being to simplistic, but I see a timeline that stretches from left to right. On the left side I see simple organisms, and while I move to the right I see forms emerging that are progressively more complex, have a greater range of possible responses to their environment, and display higher levels of self-awareness. I don’t see evolution starting with human beings 3 billion years ago and then evolution just sort of randomly wandering its way from there down into simpler creatures and up into exalted ones.

    Going to such pains to avoid being anthropocentric, especially when we’re using such fashionable pomo terms as rhizomatic, seems like the anthropological PC counterpart of being careful not to imply that one’s parent culture is not any better or worse, only different, than this or group of barbarians around the globe. The sentiment might even be right, but when sometimes it comes off as a lame affectation.

  13. franscouwenbergh

    What is wrong with Eric Chaisson’s theory of the evolution of complexity?
    Indeed >>>”Microbes, insects, and fish completely dominate life on earth and none of them are moving in this direction or progressively evolving towards complexity.”<<<, but one may say those life forms are left behind in the race towards ever moren complex means of extracting energy from their environment for sustaining and procreation of their genes.

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