The Gene Pool Metaphor
Criminal Genes and The Law




    Nature or nurture?  Is human behavior formed by the environment in which we are raised, or, are we hardwired, like computers, predestined to a personality by our genes?   As far back as the ancient Greeks, philosophers argued about whether knowledge and abilities were innate or learned.  Aristotle proposed that, at birth, our minds are blank slates ("tabula rasa").  As we develop, Aristotle argued, one's environment determines what messages are recorded on it, promoting or nurturing an individual's behavior and personality.  The "nature" position, on the other hand, describes behavior as governed by genetically predetermined signals which unfold according to a genetic blueprint, irrespective of the environment an individual inhabits.  Today, most scientists support the view that human behavior is shaped by both one's genes and the environment.

    One of the first scientists to link the discipline of molecular genetics with behavior was Seymour Benzer.  In the 1950's, Benzer had helped formulate the "one gene-one polypeptide" principle, expressly linking the concept of a gene (which he called a "cistron") to its function in coding for a single polypeptide.  By the 1970's, Benzer took the "one gene-one polypeptide" concept to a new level of abstraction, asking whether one gene could code for a single behavior.  Benzer discovered that it could.  He and his colleagues devised a learning paradigm in which they could distinguish fruit flies (Drosophila melanogaster) who learned to avoid an electric shock from those that did not.  Applying the paradigm to flies who had been treated with a chemical mutagen to alter their DNA, Benzer's group identified a "dumb" fly which carried a mutation in a single-gene.  This gene apparently played a role in learning behavior since mutating it impaired the ability of the fly to learn.   The first dumb gene was dubbed "dunce."

    The one gene-one behavior principle was expanded to mammals in 1980's when  technology emerged which enabled scientists to "knock-out" the function of normal genes in mammals.  Instead of randomly mutating genes with a chemical mutagen as they had in flies, using the tools of genetic engineering, molecular neurobiologists selectively disabled a specific gene's function and observed its effect on the animals' behavior.  The first genes targeted were those involved in neuron function and signaling, such as genes which encoded neurotransmitter receptors and enzymes involved in neurotransmitter synthesis.  The theory was that, if neurons were the building blocks of the mind, disrupting their normal function should produce an effect on the behaviors which are a product of the neuron pathways.  Using a mouse as a model organism, it was discovered that the loss of a gene's function involved in neuron physiology had significant behavior effects - affecting aggression, intelligence, and a variety of other common behaviors.  This research established a definite basis for the theory that complex behaviors are genetically-determined.

    Single-gene loci have been discovered to affect behaviors in mammals as complex as humans.  The primary evidence comes from gene-linkage studies in both unrelated and related individuals.  A family-linkage study typically begins with the discovery of a family in which a particular behavior has been observed through several generations, suggesting an inherited genetic component.  The goal is to identify a DNA marker which is present in family members who share the behavior but absent from those that don't.  Family-linkage studies have suggested a genetic basis for a number of human behaviors, including aggression, homosexuality, manic-depression, and anxiety.

    The Neurobiologist's Guide to Buddha has been designed as an inventory of genes which have been revealed by scientific studies to influence behavior and personality.  The intent of the title is to recapitulate the "nature versus nurture" debate.  Buddhism traditionally focuses on the principle that human behavior can be controlled by altering one's state of mind.  According to the Teaching of Buddha, the cause of human suffering is the "thirsts" of the human body and "the illusions of worldly passions."  Suffering can be eliminated, Buddha teaches, by controlling the mind and divesting it of desire, passion, greed, anger, fear, craving, and other destructive impulses.  "Break the bonds of worldly passions and drive them away as you would a viper."  The intent of the The Neurobiologist's Guide to Buddha is to explore these teachings by studying the genes which underlie human behaviors, and which control, and even drive, desires and worldly passions.

    Buddhism refers to the "discriminating mind" and the "pure mind of Enlightenment."  The discriminating mind is the part of the self which  focuses on the materiality of the corporeal world as it is perceived by the senses, rather than its essential nature. In making the connection between neurobiology and Buddha, the discriminating mind can be pictured as the genetically-determined self.  The machine erected on a foundation of genetically-encoded functions - receptors, neutrotransmitters, neuronal-pathways, and the like - which account for all sensory processes and behaviors.  The "pure mind of enlightenment" is more elusive.  It is the state which is achieved when the mind is perfectly controlled, "pure and tranquil," and all desires are quenched.   The question raised in The Neurobiologist's Guide to Buddha is whether a pure mind of enlightment be attained when the genes which underlie the discriminating mind dictate greed and aggression.