Structuralism does not imply that evolution runs on rails

I got a guest spot on Jackson Wheat’s channel, where he’s rebutting a guy who claims that structuralism means that evolution will inevitably lead to humans — that intelligent bipedal mammals are an ideal form that life will converge upon because it is encoded in the natural laws of the universe. That isn’t what structuralism implies at all! Gould and Lewontin’s spandrel paper is not saying that cathedrals are inevitable, but that some architectural features will emerge as a consequence of physical constraints rather than by design.

Jackson explains it all, and I intrude near the end to say a few pro-structuralist marks while totally repudiating the idea that evolution runs on invisible rails that mean certain forms are necessary.


  1. raven says

    … that intelligent bipedal mammals are an ideal form that life will converge upon because it is encoded in the natural laws of the universe.

    Simon Conway-Morris, an expert on the Burgess shale fossils says the same thing.
    Life’s Solution: Inevitable Humans in a Lonely Universe
    by Simon Conway Morris
    Life’s Solution builds a persuasive case for the predictability of evolutionary outcomes. The case rests on a remarkable compilation of examples of convergent evolution, in which two or more lineages have independently evolved similar structures and functions. The examples range from the aerodynamics of hovering moths and hummingbirds to the use of silk by spiders and some insects to capture prey. Going against the grain of Darwinian orthodoxy, this book is a must read for anyone grappling with the meaning of evolution and our place in the Universe.

    Conway-Morris is a xian and uses convergent evolution to claim that god exists, etc..

    I read the book and the science was interesting but didn’t support his conclusions.
    We don’t have the data to say that we are the only technological intelligent species in the Galaxy.

  2. hemidactylus says

    Ok I must be a bad structuralist because I don’t think humanoids are inevitable (see Gould’s Full House and Modal Bacter) nor that ecological niche constraints translate into Platonic eidos from the outside. I do believe I am a very imperfect representative [ie-ectype) of the chordate archetype indicated by Pikaia gracilens in Burgess Shale from Gould’s Wonderful Life. I share common ancestry with lancelets (amphioxus if you will) which share rudiments of my body plan.

    @5:23 is a superficial treatment emphasizing convergence. I believe in a sense with Goethe’s botanical assumption that “All is leaf”, therefore bird and bat wings, as much as they converge to support being airborne, are homologues as forelimbs as is the arm I am using to type this. Snakes show that limbs can be lost. Ectypal exceptions. But my notochordal remnants are hurting. I hate Plato for this.

    It is an insult to march Denton out and call that structuralism. Bauplane are contingent not inevitable and they constrain adaption.

    Frickin chordates and arthropods go back to the urbilaterian worm. Ok he covers that.

    Hox genes are great exemplars of conserved archetypal themes themselves at the molecular level. With duplication and divergence structure gets functionally coopted, Gould’s exaptation.

    Mayr is a mixed bag. Eyes didn’t quite evolve independently across phyla. The homologous (er…archetypal) genetic underpinnings facilitated some degree of parallelism across lineages, but advanced camera eyes of vertebrates and cephalopods display as much convergence as parallelism and homologous genetic underpinning.

    Turing seemed to inspire substrate neutral computer metaphor of cognitive science that ev psych utilizes in its modularity. Searle took a crack at this in his Chinese room metaphor. Did he succeed? This modularity of EP was scooped a bit by Jung with his thematic cultural archetypes, though cultural convergence on shared ecological issues or diffusion probably explains thematic narrative parallels better than common ancestral psychic homologues. People live near waterways. Waterways flood. In a manner similar to Bartlett’s Remembering these stories go through telephone game reconstruction. We get dramatic global flood stories around globe. One such story migrated from Ur to Israel with the mythical Abram. One plus for ev psych may come though from Dan Sperber’s cultural attractors but I digress too much. How did I get here? Where am I going. Ummmm… oh yeah!

    My “structuralist” proclivities are based on the non-Paleyian archetypal tradition of Goethe and Richard Owen and is very friendly to spandrels. Dawkins is too much a Paleyian for my tastes. Same with adaptionist psychology. I blame Jung for this. Anyway EP and spandrels…the noggin structure left an archway of self-realization perhaps based on contemplation of conspecific other minds that led to mortality salience and “other mind” projection into the universe and eventual notions of intelligent design. Ironically someone like Denton comes along and hijacks the structuralism that bequeathed distant precursors to his faith.

  3. says

    I think the point that both Jackson & I made is that you’re not a “bad” structuralist if you reject the bogus argument of the inevitability of certain archetypal form. You’re a bad structuralist if you think that extreme is supported by the evidence!

    I reviewed Conway Morris’s book, Life’s Solution when it came out. I hated it. One of the dumbest books from a prestigious scientist I have ever read.

  4. hemidactylus says

    On a second pass I am frozen on the frame at 11:15. Look at the choice of organisms. Humans vs an elephantoid. It is unclear whether elephants have passed the mirror test indicating self-awareness, but other species have. Magpies are those dinosaurs who are converging upon the scalar grade of Psychozoa. There are very smart dinosaurs among us. They have a plan…the great corvid takeover. Oops some corvids failed. But is the mirror too anthrpocentric?

    Elephants have big brains, though perhaps not as convoluted and their bodies are bigger which skews cephalic index. I have read of some anecdotes of reverence for dead, they communicate infrasonically on a rudimentary internet chat network and God help the villager or trainer that pisses one off. They never forget. But they lack opposable thumbs or they might be holding weapons of their own…oh wait:

    But anyway some nonhuman vertebrates are converging on us but are limited by lack of opposable thumbs. I’m looking at you cetacean underachievers. Dogs are a major disappointment given a paw up in the world with our help.

  5. Howard Brazee says

    He must be right, because all of the aliens on Star Trek are bipedal, and not elephine.

  6. blf says

    Not quite all Star Trek aliens; e.g., the Horta where not obviously bipedal…

    Similar thing on Doctor Who, were the often-bipedal aliens are also typical adult human-sized.

    Combined, clear proof of the hypothesis!

    (Amusingly, whilst researching this reply, I discovered there was a Doctor Who alien species known as the “Elephine” — in the novel Halflife — but have no idea what they looked like &tc (they seem to be incidental to the story?).)

  7. curbyrdogma says

    #4: We know it’s a common trope on internet forums to discuss doomsday scenarios wrt the human species and/or how the earth would be so much better off without humans. …But under that hypothetical scenario, after a few million years, would other intelligent species fill the niche that we left behind? We know that a certain dystopian sci-fi series proposed it would be the great apes. I’m thinking maybe more likely baboons, because they’re more numerous and successful as a species. Raccoons (Carnivora’s answer to primates) in North America, possibly? Corvids’ wings would limit their ability to manipulate tools and shape the environment, but they might evolve a more advanced form of groupthink and become a rather formidable force in the skies. (Imagine highly evolved baboons, raccoons and crows. Would they be any better than us? Oh well, might make an interesting premise for a video game at any rate.)

  8. chrislawson says


    There is a big element of truth to what you say about the evolution of eyes, but it is an argument to be used with care because it is often abused by directed evolutionists who accept evolution but want to believe that the form of life is the will and pre-specified design of god (which I am not claiming as your position, to be clear). The interesting (and probably correct) discovery is that comparative genetics can trace photoreceptor molecules in all known eyes back to opsins in prokaryotes and cyanobacteria around 700-1500 Mya (depending on which model you prefer) and there has been relatively little variation in their molecular structures since then.

    But the eye is not just a clump of photosensitive molecules, it is an organ that turns light into nerve signals. And it most definitely arose independently many times, which is why the mammalian eye is so different from the mollusc eye, is so different from the insect eye, is so different from the planaria eye, etc. These are not differences due to divergence from a common ancestor, these are differences that are non-commutable to each other (that is, it would be almost impossible for the vertebrate retina to evolve a structure like the far superior mollusc retina).

    And we don’t know for sure if other completely non-opsinoid receptor molecules evolved in the past in extinct branches of life. The only knowledge we have of deep ancient opsins is by mathematical modelling of existing organisms’ opsins. If there were now-extinct receptors, we have no way of recognising them given current scientific tools. So it’s possible that photoreceptor molecules evolved many times independently but we just don’t know about it.

    A nice summary.

    To claim that the eye has a common origin because of opsins is to me the same as saying wings did not develop independently in insects, birds, bats, and avian reptiles because of pax genes. Or (even worse!) that all flippers and fins are direct evolutionary descendants of microbial flagella.

  9. chrislawson says


    “Psychozoa” is a great word. May I steal it? (And if we want to include non-animals, should the term be psychobiota?)

  10. hemidactylus says

    @10 chrislawson

    The term was coined by Julian Huxley. Here’s a relevant quote from John Wilkins:

    “Classifications in terms of these ideas also became popular, leading to the eventual and inevitable (and somewhat absurd) suggestion by Julian Huxley in 1957 that since humans alone occupied the “adaptive zone” of intelligence, they should be classified in an entirely distinct major grade on a par with Metazoa, Psychozoa. Huxley explicitly discussed these in terms of grades.”

    Wilkins links to a google books snippet quoting Huxley.

    I think more species than humans earned that designation I would cast more in terms of sapience. The mirror test and tool use are problematic as indicators. I guess we could add cephalopods to make PZ happy.

    I wouldn’t add bacteria though they show that brains or neural complexity are overrated in their own simple ubiquity and ability to counter our antimicrobial measures.

    Still I think animals potentially being self aware and using tools is cool though those qualities are biased towards us.

    I have been skeptical (after first uncritically smitten) of the hype around orca cultural innovations scaring the shit out of sharks, but since I dissed cetaceans up there:

    “I ate his liver with some fava beans and a nice chianti.”

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