How to Build a Brain

Continuing with the recent book review theme, allow me to say a few words about The Accidental Mind: How Brain Evolution Has Given Us Love, Memory, Dreams and God, by David J. Linden. Linden is a professor of neuroscience at the Johns Hopkins School of Medicine.

If you have been paying attention to the creationists lately, you know they have been playing the brain card something fierce. It is here, they claim, that the bad ol’ materialist paradigm has met its waterloo. Surely so magnificent an organ can not be explained by Darwinian evolution? It just has to be the result of intelligent design, right? There just has to be some non-material mind stuff wafting around inside the skull, right?

The creationists have provided little in the way of arguments or data for this position, preferring instead the “Gee Whiz!” style of argument at which they excel. Having waded through some of their maunderings on the subject, I can say with great satisfaction that Linden’s book is a breath of fresh air. It lays out, as accessibly as is possible, what is known about the structure and inner workings of the brain. It also comes to a clear conclusion regarding the merits of ID arguments as applied to the brain. Forgive the long quote, but it is worth enjoying in full:

Is the evidence for design in biological systems so obvious? I hold that the brain, the ultimate test case, is, in many respects, a true design nightmare. Let’s review a bit. When we compare the human brain to that of other vertebrates, it becomes clear that the human brain has mostly developed through agglomeration. The difference between the lizard brain and the mouse brain does not involve wholesale redesign. Rather, the mouse brain is basically the lizard brain with some extra stuff on top. Likewise, the human brian is basically the mouse brain with still more stuff piled on top. That’s how we wind up with two visual systems and two auditory systems (one ancient and one modern) jammed into our heads. The brain is built like an ice cream cone with new scoops piled on at each stage of our lineage.

Accidental design is even more obvious at the cellular level in the brain. The job of neurons is to integrate and propagate electrical signals. Yet, in almost all respects, neurons do a bad job. They propagate their signals slowly (a million times more slowly than copper wires), their signaling range is tiny (0 to 1,200 spikes/second), they leak signals to their neighbors, and, on average, they successfully propagate their signals to their targets only about 30 percent of the time. As electrical devices, the neurons of the brain are extremely inefficient.

So, at either the systems or cellular level, the human brain, which the intelligent design crowd would imagine to be the most highly designed bit of tissue on the planet, is essentially a Rube Goldberg contraption. Not surprisingly, some proponents of intelligent design have left themselves a way to retreat on this point. Michael Behe writes, “Features that strike us as odd in a design might have been placed there by the designer for a reason — for artistic reasons, for variety, to show off, for some as-yet-undetectable practical purpose or for some unguessable reason — or they might not.” Or, stated another way, if on first glimpse biological systems look cool, that must be the result of intelligent design. If, on closer inspection, biological systems look like a cobbled-together contraption, that’s still got to be from intelligent design, just intelligent design with an offbeat sense of humor. Clearly, this position is not a true, falsifiable scientific hypothesis, as is the theory of evolution. The idea of intelligent design is merely and assertion. (pp 241-242).

This sort of argument is a powerful one in favor of evolution. Stephen Jay Gould famously popularized it in the case of the Panda’s Thumb:

Thus, the paradox: Our text books like to illustrate evolution with examples of optimal design–nearly perfect mimicry of a dead leaf by a butterfly or of a poisonous species by a palatable relative: But ideal design is a lousy argument for evolution, for it mimics the postulated action of an omnipotent creator. Odd arrangements and funny solutions are the proof of evolution–paths that a sensible God would never tread but that a natural process, constrained by history, follows perforce. No one understood this better than Darwin. Ernst Mayr has shown how Darwin consistently turned to organic parts and geographic distributions that make the least sense for his defense of evolution.

The point of the argument is not, as some creationists try to pretend, that bad design equals no design. We are not measuring complex biological systems against some arbitrary standard of perfection, finding them wanting, and concluding that there is no design in nature.

Instead the point is that no matter where you look, the complex adaptations that suggest design on a cursory inspection turn out to have just the properties they ought to have if they were produced gradually by natural selection. For Gould it was the Panda’s thumb, which was not a thumb at all but merely a bony appendage formed by modifying structures possessed by the panda’s relatives for other reasons. For Linden it is the human brain, which arose by piling new add ons to old structures.

This pattern is ubiquitous. Creationists often make much of the fact that it is difficult to discuss evolution without design language (like saying that eyes are designed for seeing and wings for flying.) But it is even more difficult to discuss evolution without using words like “Rube Goldberg” and “cobbled together.” Whether we are talking about the eye, the blood clotting cascade, the immune system, our process of embryological development, or just about any other complex system ever studied in detail, we find they are never novel, pristine creations, but seem always to be built by modifying more ancient structures.

There is an irony. Complex adaptations, once thought to be clear evidence of design, actually provide some of the strongest evidence for evolution by natural selection that we have. Creationists are stuck at the “Gee whiz!” level of biological analysis. For people who actually study these systems in detail, the illusion of design disappears pretty quickly.

I don’t mean to give the impression that Linden’s book is primarily a response to the creationists. That’s really just an afterthought, albeit one that especially resonated with me given my somewhat eclectic interests. Most of the book is just a clear and enjoyable discussion of the physical structure of the brain, and how understanding this structure sheds light on some basic mysteries of human cognition.

Highly recommended.


  1. #1 AL
    January 4, 2009

    I don’t get why the ID crowd would even bother to be enamored with the complexities of the human brain. Most of them are dualists, so they believe that consciousness and intelligence exists apart and disembodied from brains anyhow. I mean, they’ve taken away the very things that make brains amazing and reduced them to lumps of neural tissue…yet they want to still tell us that the brain is amazing — so amazing, in fact, that it must’ve been designed by an aforementioned disembodied intelligence!

  2. #2 John Farrell
    January 4, 2009

    <>Creationists often make much of the fact that it is difficult to discuss evolution without design language (like saying that eyes are designed for seeing and wings for flying.) But it is even more difficult to discuss evolution without using words like “Rube Goldberg” and “cobbled together.”

    Exactly. This can’t be pointed out often enough, far as I’m concerned.

  3. #3 Derek James
    January 4, 2009

    I read Linden’s book, too, and yes, it’s very good and highly recommended.

    However, while I buy his arguments for the macro-level organization of the brain as evidence for evolution, I think he’s on shakier ground when talking about how neurons operate. The speed, noise, and leakage of neurons may all be features, not bugs. The fact is, our ignorance regarding how brains do what they do is still enormous, and without an integrative theory of cognition, it’s a little specious to talk about how the spike rate or conductance of neurons is suboptimal, and would somehow work much better on another substrate, e.g. replacing axons with copper wire.

  4. #4 J Boules
    January 4, 2009

    “If, on closer inspection, biological systems look like a cobbled-together contraption, that’s still got to be from intelligent design, just intelligent design with an offbeat sense of humor.”
    Seems to me this falsifies the design argument all together, since what could be funnier than letting the design argument continue, while the designer let evolution proceed unchecked all the time.
    It would also negate a personal god since who wants to pray to a whimsical being.

  5. #5 Raymond Minton
    January 4, 2009

    And please don’t forget backwards retinas, the two sets of dummy kidneys before we get our final pair, the appendix that once stored vegetation but is now subject to exploding and killing us, the urethra running through the prostrate, on and on. Far from showing “intelligence’, the brain and other aspects of human anatomy only serve to show how slipshod and messy natural selection can be. If this is the work of a designer, maybe he\she\it should take up another line of work!

  6. #6 Mike
    January 4, 2009

    It is interesting to think about what other possible uses there are for suboptimal neuron communication, leakage and the like. The nice thing about evolution is that a future human brain may contain a better mechanism. A different ion transmitter or better isolation. A small change could make a big difference. We could all be the interim forms on the way to a more highly evolved brain. Pretty cool.

  7. #7 Johnrap
    January 5, 2009

    Horticulture and animal husbandry were understood and in practice before Darwin wrote his books. Synthetic biology, genetic engineering and artificial intelligence are all in practice and expanding utility today. These book ends means that Darwin has maximum 150 years of relevance.

    Darwin’s main contribution, not the man Darwin, but the folks who talk about him afterward seems only to be an assumption that modern earth humans are the first to engage in the current technologies.

    Congratulations, I guess, if 150 years of rebranding natural laws of biology as an argument in favor labeling humanity the universe’s most intelligent product is really something you feel good about.

  8. #8 David Harmer
    January 5, 2009

    I’m really completely baffled as to why there is any discussion at all as to “Intelligent Design” being a scientific theory. Any and all scientific theories must contain a condition under which they may be proven false. It doesn�t make any difference whose theory it is: Einstein�s, Newton�s, Darwin�s or Joe Smuck�s.

    The problem with the theory of an Intelligent Designer is that it is not a theory at all. It is a philosophical idea like philosophy, ethics, religion, government, etc. Why, because no one can ever prove that an intelligent designer exists. Science demands critical, verifiable, repeatable evidence. It is impossible for the IDer crowd to provide that. Call him what you may: he, she or it is only a figment of the imagination and that is not what science is about. Darwin�s theory, on the other hand does provide the evidence and it is what modern medicine, biology (to name a few sciences) is based upon. Does it have all the answers? Not at the moment because we are just beginning to find answers through good scientific research going on around the world using Darwin�s ideas. ID is a handicapped idea, not a theory, and those who promote are even more so.

  9. #9 Bil Rohan Sr
    January 5, 2009

    The idea of intelligent design is merely and assertion. (pp 241-242).

    Too bad. This misprint deflects attention from the most important fact of all. All religious claims are assertions

  10. #10 Bil Rohan Sr
    January 5, 2009

    It is worthwhile to remember that consciousness is not yet explained in empirical terms.

  11. #11 AL
    January 5, 2009

    It is worthwhile to remember that consciousness is not yet explained in empirical terms.

    It is worthwhile to remember that consciousness is not yet fully explained, period. There is no need to single out empirical explanations in particular, as non-empirical dualist “explanations” don’t explain anything.

  12. #12 nonserviam
    January 8, 2009

    Ironically, SJG immediately turns from an evolutionist into a blank-slater when the subject is human biodiversity.

  13. #13 bric
    January 9, 2009

    Interestingly, it was on exactly this point that Wallace eventually disagreed with Darwin; not from religious conviction but apparently as a result of belief in spiritualism.

  14. #14 K
    January 13, 2009

    I’m amazed at how people think that evolution makes so much more sense than intelligent design! Just look at a cell, DNA, protein synthesis, translation, and tell me that this all happened “somehow” by chance.

    “The idea of intelligent design is merely an assertion”

    The idea of evolution is merely an assertion too!!!

    And to me a silly assertion at that. No one will ever be able to “prove” evolution. And apparently no one will ever accept the proof of intelligent design because they are blinded by the evolution theory.

  15. #15 Jim Thomerson
    January 14, 2009

    As I recall the story, Wallace had the unusual, for his time, thought that simple tribal people were as intelligent as upper class Englishmen. But he thought their simple lives did not require this high level of intelligence; therefore, it could not be the result of natural selection. When I took a course in cultural anthropology in 1955, there was considerable emphasis of the idea that the simple tribal life was just as complex as ours; that a tribal shamen had as much knowledge as an MD, and the like.

  16. #16 Eric Thomson
    January 16, 2009

    I never liked these “look it’s suboptimal” arguments against Creationism. For instance, neurons may work at the optimal time scale for interacting with the things they have to interact with (e.g., you wouldn’t want them to work as quickly as a silicon chip). The failure of synaptic release at individual neurons (e.g., in cortex only 10% of presynaptic spikes actually lead to neurotransmitter release) could be a useful design feature that keeps the brain from “exploding” (i.e., going into some massive epileptic seizure or runaway neuronal excitation). Plus, who cares if we have multiple visual areas. They do different things so it’s not like there is the exact same transformation of ambient EM waves going on.

    That said, it is not surprising that the creationists are going after the brain now. I’ve started a series on their attacks on consciousness, first post here.

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