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How can a small number of genes build a complex mental machine?
Permanent link to this article: http://www.kurzweilai.net/meme/frame.html?main=/articles/art0387.html
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How can a small number of genes build a complex mental machine?
We have only around 35,000 genes, but tens of billions of neurons. How does a relatively small set of genes combine to build a complex brain? Gary F. Marcus responds to Edge publisher/editor John Brockman's request to futurists to pose "hard-edge" questions that "render visible the deeper meanings of our lives, redefine who and what we are."
Originally published January 2002 at Edge. Published on KurzweilAI.net January 21, 2002. Read Ray Kurzweil's Edge question here.
John McCarthy and I are from different generations (in the semester before McCarthy invented Lisp, he taught my dad FORTRAN, using punch cards on an old IBM) but our questions are nearly the same. McCarthy asks "how are behaviors encoded in DNA"?
Until recently, we were not in a position to answer this question. Few people would have even had the nerve to ask it. Many thought that most of the brain's basic organization arose in response to the environment. But we know that the mind of a newborn is far from a blank slate. As soon as they are born, babies can imitate facial gestures, connect what they hear with what they see, tell the difference between Dutch and Japanese, and distinguish between a picture of a scrambled face and a picture of a normal face. Nativists like Steven Pinker and Stanislas Dehaene suggest that infants are born with a language instinct and a "number sense". Since the function of our minds comes from the structure of our brains, these findings suggest that the microcircuitry of the brain is innate, largely wired up before birth. The plan for that wiring must come in part from the genes.
The DNA does not, however, provide a literal blueprint of a newborn's mind. We have only around 35,000 genes, but tens of billions of neurons. How does a relatively small set of genes combine to build a complex brain? As Richard Dawkins has put it, the DNA is more like a recipe than a blueprint. The genome doesn't provide a picture of a finished product, instead it provides a set of instructions for assembling an embryo. Those instructions govern basic developmental processes such as cell division and cell migration; it has long been known that such processes are essential to building bodies, and it now is becoming increasingly clear that the same processes shape our brains and minds as well.
There is, however, no master chef. In place of a central executive, the body relies on communication between cells, and communication between genes. Although the power of any one gene working on its own is small, the power of sets of genes working together is enormous. To take one example, Swiss biologist Walter Gehring has shown that the gene pax-6 controls eye development in a wide range of animals, from fruit flies to mice. Pax-6 is like any other gene in that it gives instructions for building one protein, but unlike the genes for building structural proteins like keratin and collagen because the protein that pax-6 builds serves as a signal to other genes, which in turn build proteins that serve as signals to still other genes. Pax-6 is thus a "master control gene" that launches an enormous cascade, a cascade of 2,500 genes working together to build an eye. Humans that lack it lack irises, flies that lack it lack eyes altogether. The cascade launched by pax-6 is so potent that when Gehring triggered it artificially on a fruit fly's antenna, the fly grew an extra eye, right there on its antenna. As scientists begin to work out the cascades of genes that build the brain, we will finally come to understand the role of the genes in shaping the mind.
Copyright © 2002 by Edge Foundation, Inc.
www.edge.org
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article by G.Marcus, Brains from Genes
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The question makes sense, the proposed answer neither.
The article may be too short for going into details. The article, however, addresses the question in the wrong way.
(So far I do not know either, but probably soon)
Well, what is going wrong with the way G.Marcus approaches this issue?
Basically, hoping for the geneticists distracts the physical realm and the realm of meaning.
David Marr pointed it out as early as 1981 (shortly before he died, unfortunately). There is a level of physical realization (genes), algorithmic representation (mechanisms) and computational framework (capability for meaning). Arguing on the level of genes and hoping for a solution is like being an amoeba thinking about complexity.
The brain is a semiosic entity (see C.Peirce), capable for meaning. What is meaning? Take a look to Wittgenstein's Philosophy of Psychology. They moved towards a more useful direction than the naive reductionism does.
Any answer about the brain will be accessible only after answering the following questions
- What is novelty?
- What is a function?
- What is a process?
- What is similarity?
- What is meaning?
only to give a small number of relevant questions. The issue of Pax-6 will never be relevant for questions about meaning, consciousness and intelligent self-organised problem-solving.
regards
Klaus Wassermann
23-1-02
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Re: How can a small number of genes build a complex mental machine?
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To me, innate nest-building skills seem rather "fuzzy" as opposed to higher concepts such as mathematics & spoken languages.
These various species of bird have instincts for scavenging material & weaving it together in concave clusters.
Math & language have complex sets of rules & esoteric concepts. To implement them explicitly would require the biological equivalent of a ROM-like database, different than our algorithmic genes. It would be like trying to breed an orchid that had the lyrics from "Stairway to Heaven" printed on it's petals.
I do suppose, however, that DNA could be optimized to focus more resources upon the development of structures & mechanisms most supportive of linguistic or logical talent. For example, a subject might be tailored to posses a greatly increased portion of brainspace to rote memory, or even the perception of thoughts & feelings in others (& one's own self) as language is so much more than memorization. It is eye contact, body language, tone of voice, innuendo, and so on. The faculties dealing with these subtle arts might well be strengthened.
Such an optimized subject may easily absorb a dozen languages as simply as we learn a single native tongue. But, of course, I conjecture... |
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Re: How can a small number of genes build a complex mental machine?
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Just throwing in a bit of old fashioned philosophy here, but Sagan, I believe, pointed out that the brain developed when genes could no longer code necessary information. Since that information was no longer capable of being coded in a programmed fashion, the brain would represent alternatives or "sworls" of options that are limited within the genetic replicative algorithm for each species.
Societies are built to limit the choices created in the development of the brain, and those societies follow sociobiological patterns that limit reproduiction through ritual behavior gearded to territory.
Sopcial behavior adapts to specific territory and responds by limiting its opitions to avoid stresses involved in change.
It would seem that what is generated by the combination of genes is merely a general pattern that is enlarged to enhance reproductive success.
The organism is "informed" however, by a virus or bacteria that invades the organism and causes a response of defense and attack to presefve internal integrity.
Two beneficial results occur:
1. The organism goes through a purification process(diarrhea, vomiting, etc) to rid itself of the invader.
2. In identifying the invader, the immune system is enhanced because it has enlarged its "library" of defenses and created an antibody to eliminate the invader. This means that adaptive "intelligence" in general is also enhanced.
This adaptive process incorporates the viral invader into the organism and alters the reproductive process at the cellular level, but only to the extent necessary for adaptation.
The genes, therefore, interact with a totality of genetic structures provided by the environment, usually in the form of viruses, which are merely genetic bits encased in protein.
The "junk DNA" is similar to viruses in their make-up, and may be part of the organism's adaptive response, each bit of DNA corresponding to bits of viral invading DNA, and reacting to form new reproductive behaviors, which may include speciation to new territory, or even an expansion of the species as its adaptabilioty is enhanced.
After these changes occur, the species may evolve new ritual behavior to separate their reproductive processes from similar species.
That same process of ritualization becomes more complex in humans, but at the core of the various rituals lies a replicative algorithm which follows basic patterns that remain similar in many respects.
Complexity increases, but processes can return to basic desires and instincts to maintain reproductive integrity.
The genes, therefore, only have to produce replicative patterns, and those patterns will form into more complex representations, but the complexity always revolves around efficient replicative strategies that are interchangeable.
The human brain has by-passed the necessity of speciation folloowed by animals, buit has merely evolved the replicative algorithm to non-biological processes, so that interchangeability becomes "homogenized" to the degree that we can explore "foreign" areas of thought and apply it in context to change.
It seems to me that both arguments above are correct, but do not take into account the fact that our genes exist within a sea of environmental genes that interact with our own to create new and complex adaptive strategies. |
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