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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.
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