January 13, 2006 | David F. Coppedge

Why Your Brain Has Gray Matter, and Why You Should Use It

Vertebrate brains have an outer layer of “gray matter” over the inner “white matter.”  Why is this?  “By borrowing mathematical tools from theoretical physics,” a press release from Cold Spring Harbor Laboratory announced, two researchers found out.

Based on no fewer than 62 mathematical equations and expressions, the theory provides a possible explanation for the structure of various regions including the cerebral cortex and spinal cord.  The theory is based on the idea that maximum brain function requires a high level of interconnectivity among brain neurons but a low level of delays in the time it takes for signals to move through the brain.   (Emphasis added in all quotes.)

Their paper was published in PLoS Computational Biology.1  Despite the implicit deduction that the brain appears optimally designed, the authors looked to the random, unguided processes of evolution to explain how it got that way.  Notice the first word in this next sentence: “Assuming that evolution maximized brain functionality, what is the reason for such segregation?”  they asked.  Did the claim of evolution ever get past the assumption stage?

Gray matter contains neuron somata, synapses, and local wiring, such as dendrites and mostly nonmyelinated axons.  White matter contains global, and in large brains mostly myelinated, axons that implement global communication.  What is the evolutionary advantage of such segregation?  Networks with the same local and global connectivity could be wired so that global and local connections are finely intermixed.  Since such design is not observed, and invoking an evolutionary accident as an explanation has agnostic flavor, we searched for an explanation based on the optimization approach, which is rooted in the evolutionary theory.

Their use of the term agnostic is not what most people think (i.e., uncertainty about the existence of God), but a-gnostic, or “not knowing.”  They understood, in other words, that saying it was a lucky accident is a non-answer.  Rather, they assumed that evolutionary theory provides a pathway through the randomness toward optimization.  They stated again that this was their starting assumption:

We started with the assumption that evolution “tinkered” with brain design [sic] to maximize its functionality.  Brain functionality must benefit from higher synaptic connectivity, because synaptic connections are central for information processing as well as learning and memory, thought to manifest in synaptic modifications.  However, increasing connectivity requires adding wiring to the network, which comes at a cost.  The cost of wiring is due to metabolic energy required for maintenance and conduction, guidance mechanisms in development, conduction time delays and attenuation, and wiring volume.

Sounds like a lot of engineering talk.  The scientists assumed, but did not demonstrate in this paper,2 that natural selection was up to the task of yielding this optimized entity sometimes called the most complex assemblage of matter in the known universe.


1Quan Wen and Dmitri B. Chlovskii, “Segregation of the Brain into Gray and White Matter: A Design Minimizing Conduction Delays,” Public Library of Science Computational Biology, Volume 1 | Issue 7 | December 2005.
2Here are the only other mentions of evolution in this paper:

  • “Although wiring volume minimization is an important factor in the evolution of brain design, [earlier] results remain inconclusive…”
  • “Finally, it is likely that, in the course of evolution, minimization of conduction delay was accompanied by the increase in connectivity.”
  • “In a neurobiological context this means a combination of high computational power in local circuits with fast global communication.  Thus it is not surprising that evolution adopted this architecture when the size of the network made all-to-all connectivity impractical.”
  • “Although we do not know whether competing desiderata of short time delay and high interconnectivity were crucial factors driving evolution of vertebrate brains, our theory makes testable predictions.  Below, we compare these predictions with known anatomical facts.”  (These concerned measurements of cortical thickness and brain size among various vertebrates.)
  • “In general, the evolutionary cost is likely to include both the volume and the time delay.”

In none of these references to evolution were specific details provided about how the variations occurred, how they added up, and how they converged on a variety of vertebrate brains, each composed of billions of neurons that function together as an optimized unit.

Brains are mathematically perfect for achieving the sweet spot between maximized interconnectivity and minimized transmission delays.  The authors reminded us that a human brain contains about 10 billion neurons, and that each one can contain thousands of connections with other neurons.  The two-layer structure meets the competing requirements to a T.  That part is amazing.  Assuming that evolution did it earns this entry the Dumb award – really dumb.
    Here again we are told about another apparition of the goddess of the Darwin Party, Tinker Bell.  As the legend goes, she flitted aimlessly around the Cambrian swamps about 500 million years ago, zapping some emerging vertebrates with her mutation wand, killing countless myriads of them till one emerged lucky enough to have the beginnings of an optimized brain.  As animals evolved, this process was repeated myriads of times more over millions of years, producing larger and more complex brains.  Finally, at the end of the line, computational biologists emerged who could look back and analyze the whole process with abstract reasoning and mathematical equations, concluding that evolution had produced an optimized brain.  Let us ask these true believers a simple question.  If the brain evolved, how can you be sure of anything, including the proposition that the brain evolved?  (From experience, we know that posing this type of question to a Darwinist is like putting a moron in a round room and telling him there is a penny in the corner.)
    By assuming evolution at the outset, these computational evolutionists have provided as much insight into the origin of the brain as the vain mathematician did in the “assume we have a can opener” joke in the 12/17/2005 commentary.  Their logic is as follows: Assume evolution produces optimized structures.  An optimized brain would be structured so as to maximize interconnectivity and minimize delays.  The brains we observe accomplish this by segregating highly-connected neurons in a gray matter layer and long axons in a white matter layer, thus fulfilling both requirements in an exquisite product that is the most complex device in the universe, that took us 62 simultaneous equations to describe.  Isn’t evolution wonderful?
    Undoubtedly this paper will be dutifully added to the growing corpus of scripture that the Darwin Party can hold up at school board meetings to show that the peer-reviewed scientific journals are filled with evidence for evolution, and that nothing in biology would make sense without it.  Anyone raising his hand and saying, but to me, that looks like design would be quickly answered with, “Excuse me, we are talking about science here.  If you want to change the subject to religion, go to church.”
    Assumption is the mother of all myths.  Perhaps you have heard the etymology of the word ASSUME: making an ASS (donkey) out of U and ME.  Having gray matter is one thing.  Using it is another.

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