Blame that on the mischievous Genes…
Human Genome Project
identifies genes that are responsible for traits like homosexuality, alcoholism
and tobacco addiction.
By Express Reporter
Now, you can actually pass the blame on the mischievous genes for being addicted
to tobacco and liking alcohol a bit too much. Or preferring a musical pitch over
another. Researchers in the field of behavioral genetics have asserted claims
for a genetic basis of numerous physical behaviors, including homosexuality,
aggression, impulsivity, and nurturing. A growing scientific and popular focus
on genes and behavior has contributed to a resurgence of behavioral genetic
determinism—the belief that genetics is the major factor in determining
behavior.
Traditional research strategies in behavioral genetics include studies of twins
and adoptees, techniques designed to sort biological from environmental
influences. More recently, investigators have added the search for pieces of DNA
associated with particular behaviors, an approach that has been most productive
to date in identifying potential locations for genes associated with major
mental illnesses such as schizophrenia and bipolar disorder. Yet even here there
have been no major breakthroughs, no clearly identified genes that geneticists
can tie to disease. The search for genes associated with characteristics such as
sexual preference and basic personality traits has been even more frustrating.
Genetics and molecular biology have provided some significant insights into
behaviors associated with inherited disorders. For example, we know that an
extra chromosome 21 is associated with the mental retardation that accompanies
Down's syndrome, although the processes that disrupt brain function are not yet
clear. We also know the steps from gene to effect for a number of single-gene
disorders that result in mental retardation, including phenylketonuria (PKU), a
treatable metabolic disorder for which all newborns in the United States are
tested.
In general, it is easier to discern the relationship between biology and
behavior for chromosomal and single-gene disorders than for common, complex
behaviors that are of considerable interest to specialist and nonspecialist
alike. So the former are at the more informative end of a sliding scale of
certainty with respect to our understanding of human behavior. At the other end
of the scale are the hard-to-define personality traits, while somewhere in
between are traits such as schizophrenia and bipolar disorder—organic diseases
whose biological roots are undeniable yet unknown and whose unpredictable onset
teaches us about the importance of environmental contributions, even as it
reminds us of our ignorance.
Are behaviors inbred, written indelibly in our genes as immutable biological
imperatives, or is the environment more important in shaping our thoughts and
actions? Such questions cycle through society repeatedly, forming the public
nexus of the "nature vs. nurture controversy," a strange locution to biologists,
who recognize that behaviors exist only in the context of environmental
influence. Nonetheless, the debate flares anew every few years, reigniting in
response to genetic analyses of traits such as intelligence, criminality, or
homosexuality, characteristics freighted with social, political, and legal
meaning.
What social consequences would genetic diagnoses of such traits as intelligence,
criminality, or homosexuality have on society? What effect would the discovery
of a behavioral trait associated with increased criminal activity have on our
legal system? If we find a "gay gene," will it mean greater or lesser tolerance?
Will it lead to proposals that those affected by the "disorder" should undergo
treatment to be "cured" and that measures should be taken to prevent the birth
of other individuals so afflicted?
There are several scientific obstacles to correlating genotype (an individual's
genetic endowment) and behavior. One problem is in defining a specific endpoint
that characterizes a condition, be it schizophrenia or intelligence. Another
problem is in identifying and excluding other possible causes of the condition,
thereby permitting a determination of the significance of a supposed
correlation. Much current research on genes and behavior also engenders very
strong feelings because of the potential social and political consequences of
accepting these supposed truths. Thus, more than any other aspect of genetics,
discoveries in behavioral genetics should not be viewed as irrefutable until
there has been substantial scientific corroboration.
How do genes influence behavior?
No single gene determines a particular behavior. Behaviors are complex traits
involving multiple genes that are affected by a variety of other factors. This
fact often gets overlooked in media reports hyping scientific breakthroughs on
gene function, and, unfortunately, this can be very misleading to the public.
For example, a study published in 1999 claimed that overexpression of a
particular gene in mice led to enhanced learning capacity. The popular press
referred to this gene as "the learning gene" or the "smart gene." What the press
didn't mention was that the learning enhancements observed in this study were
short-term, lasting only a few hours to a few days in some cases.
Dubbing a gene as a "smart gene" gives the public a false impression of how much
scientists really know about the genetics of a complex trait like intelligence.
Once news of the "smart gene" reaches the public, suddenly there is talk about
designer babies and the potential of genetically engineering embryos to have
intelligence and other desirable traits, when in reality the path from genes to
proteins to development of a particular trait is still a mystery.
With disorders, behaviors, or any physical trait, genes are just a part of the
story, because a variety of genetic and environmental factors are involved in
the development of any trait. Having a genetic variant doesn't necessarily mean
that a particular trait will develop. The presence of certain genetic factors
can enhance or repress other genetic factors. Genes are turned on and off, and
other factors may be keeping a gene from being turned "on." In addition, the
protein encoded by a gene can be modified in ways that can affect its ability to
carry out its normal cellular function.
Genetic factors also can influence the role of certain environmental factors in
the development of a particular trait. For example, a person may have a genetic
variant that is know to increase his or her risk for developing emphysema from
smoking, an environmental factor. If that person never smokes, then emphysema
will not develop.