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.