Genetics Articles Guide
Name _____________________________
Period _____ Date __________________
Scientists’ Debate: Nature or Nurture?
1. Is finding which genes go with which behavior considered easy or difficult? Explain why.
2. The article explains that the genetic make-up and environment are inextricably linked in
controlling a person’s behavior. What do researchers believe is the role of the genetic blueprint?
What occurs based on a person’s experiences (environment)?
3. What point of view concerning the connections between genes and infidelity is portrayed in this
article? Do you agree or disagree?
Researchers Identify Gene Linked to Impulsiveness
4. What does the gene identified control (how does it affect cells)? What personality traits do people
with this gene have?
5. Does the author of this genetic study believe insurance agencies and employers should have access
to genetic information? What do you think?
The Genetics of Bad Behavior
6. Explain the effects of the gene mutation described on the body. (What problems result when not
enough of the MAOA enzyme is produced?) What kind of behavior results?
Summary Questions
7. What are some of the similarities among the three articles?
8. What are some of the differences among the three articles?
9. If you could have a genetic test done that would give you information about your
personality/behavior, would you want to have it done? Explain why or why not.
Scientists’s Debate: Nature Or Nurture?
Article by William Allen
Post-Dispatch Science Writer
A recent report that humans are genetically
programmed for infidelity is a simplistic leap of
logic, local scientists say.
“When people say we’re born to be
unfaithful, it’s like saying we’re born to be
gamblers, drug addicts or alcoholics,” said Dr. C.
Robert Cloninger, a psychiatrist at Washington
University School of Medicine.
“It’s just not that simple,” said Cloninger,
who studies the genetic basis of personality. He
reflected the view of several scientists who study
the relationship of genes and behavior.
At issue is a long-standing debate among
scientists about whether genetic makeup or
lifetime experiences – nature or nurture – most
shape personality and character. The debate has
revived in recent years as new technology made
it possible for scientists to begin mapping out the
functions of specific genes in the human genetic
blueprint carried by the DNA in our
chromosomes.
As they discover specific genes for physical
traits and for such maladies as Huntington’s
disease, they’re also finding tantalizing signs that
genes influence our behavior much more than
previously thought.
But finding which genes lead to which
behaviors is incredibly hard. That’s partly
because many genes may be involved in any
given type of behavior – from simple
cheerfulness to more complicated traits like
infidelity, criminality and even a taste for Scotch
and soda.
Still less clear are the enormously complex
interactions between the genetic code --- which
dictates the basic structure of circuits in the brain
– and the life experiences that further shape
those circuits.
Researchers believe that a person’s genetic
blueprint instructs the developing body how to
build the brain’s basic circuits. The billions of
circuits in that three-pound mass connect and fall
apart according to the person’s experiences –
from touching a hot stove to reading a book. Out
of those circuits come character and personality.
That’s why a person’s genetic makeup and
environment are inextricably linked, scientists
say.
“The more we learn, the more we see that it
is not at all an either-or situation,” said Dr.
Judith Miles, who leads a study of genetics and
autism at the University of Missouri School of
Medicine in Columbia.
Said Washington University’s Dr. Theodore
Reich, who helps lead a national study of
genetics and alcoholism: “We’re forced to study
the full complexity of it.”
The Keeping of Harems
The intriguing report on infidelity came last
month in a Time magazine essay by writer
Robert Wright, in which he adapted arguments
from his soon-to-be-published book, “The Moral
Animal: Evolutionary Psychology and Everyday
Life.”
The human mind makes use of emotions
ranging from lust to revulsion in its evolutionary
quest to transmit genes from one generation to
the next, Wright says. These emotions draw us
into and push us out of bonds with the opposite
six – including marriages.
To support this view, he cites evidence
ranging from the size of primate testicles to
reports of sexual promiscuity in n early 1,000
past or present human societies.
Wright concludes: “While both sexes are
prone under the right circumstances to infidelity,
men seem much more deeply inclined to actually
acquire a second or third mate – to keep a
harem.”
Personality Has Many Facets
Several scientists said a behavior as complex
as infidelity is not likely to be strictly
programmed in the human genetic code.
For one thing, human personality has many
different facets, said Washington University’s
Cloninger.
His studies of the behavior of identical twins
raised apart from one another have revealed two
main aspects of personality: temperament and
character.
Temperament can be thought of as “your
automatic-response pattern or emotional
predisposition,” he said.
This largely inherited personality aspect
gives a person a tendency to be quick-tempered,
warm and loving, curious, extravagant,
impulsive or any of several other possible traits.
Character is shaped by a person’s maturity,
goal-directedness and sense of values. It is
strictly uninherited.
“This is what parents and psychotherapists
try to shape,” Cloning said. “It defines the
meaning of life for you and gives you an ability
to regulate your emotional impulses in relation to
your goals and values.”
The shape of personality is further
complicated by the different ways people learn
and remember habits, skills and concepts.
And that’s why scientists doubt that infidelity
– or any other human behavior – is strictly
dictated by our genetic blueprints.
“A lot of very interesting speculation comes
codified as scientific fact,” said Jane PhillipsConroy, a Washing ton University scientist who
studies the behavior of primates. “Sometimes
that speculation is tantalizing and kind of sexy,
because it is often about sex.”
But a deeper look usually shows little hard
evidence to support it.
“We know so little about primate societies,
there’s even less of a basis for wild speculation
on humans,” Phillips-Conroy said. “But it’s fun
to read about.”
Researchers Identify Gene Linked to Impulsiveness
New York (AP)
Scientists say they’ve identified a gene that
influences how impulsive, excitable, quicktempered and extravagant you are, a possible
step toward unraveling the genetics of
personality.
Two studies provide the first confirmed
association between a particular gene and a
normal personality trait --- in this case, a
characteristic scientists call “novelty-seeking”
which includes impulsiveness, excitability and
the like.
Previous studies have shown more generally
that genes influence personality, as do a person’s
life experiences.
As scientists discover more individual genes
that affect particular traits, it might open the door
to identifying people at risk for problems such as
drug abuse and counseling them on how to lower
their risk, said research Richard Ebstein.
It might also add a twist to the issue of who’s
entitled to know about a person’s genetic
makeup.
An insurance company might want to know
that “genetically you’re a thrill-seeker and enjoy
jumping out of airplanes in a skydiving club and
taking risks in general,” said Ebstein, director of
research at the Sarah Herzog Memorial Hospital
in Jerusalem.
Ebstein is the lead author of one study of the
gene in the January issue of the journal Nature
Genetics. The second study reproduced
Ebstein’s results in a different population.
“This is major news,” said psychologist
Brian Gladue, who studies the biology of
behavior at the Institute for Policy Research at
the University of Cincinnati.
“This is going to open up a whole new field
of molecular personality research,” he said.
The discovery provides “the first missing
link” between genes and personality by
implicating a particular communication system
in the brain, Gladue said.
In that communication system, brain cells
signal one another with a chemical messenger
called dopamine. Dopamine is secreted by
signaling cells and delivers its message by
binding to receptors on the surface of receiving
cells.
The gene identified in the study tells cells
how to make one kind of dopamine receptor.
The studies found that, on average, people
with a particular version of the gene score about
10 percent higher for novelty-seeking on
personality tests that people who lack that
version.
People who are above average on noveltyseeking are impulsive, fickle, excitable, quicktempered and extravagant, while those scoring
below average tend to be reflective, rigid, loyal,
stoic, slow to anger and frugal.
About 15 percent of people in Israel, Europe
and the United States carry the novelty-seeking
form of the gene. But just why it would
encourage novelty-seeking is still a mystery,
Ebstein said.
About half the novelty-seeking variation
between people is thought to be due to genes,
and the gene in the study accounts for about onefifth of the genetic component, Ebstein said.
The gene’s effect is too small to help an
insurance company or prospective employer
judge an applicant, sad Dr. Jonathan Benjamin,
lead author of the second study. And he said he
believed they shouldn’t have access to such
information.
Ebstein’s results came from 124 adults in
Israel who filled out a personality questionnaire
and gave blood samples so their genes could be
analyzed.
Ebstein’s findings were reproduced in a
study of 315 Americans by Benjamin and
colleagues at the National Institute of Mental
Health and the National Cancer Institute in
Bethesda, Md. Benjamin is now assistant
director of psychiatry at Sorka Hospital in
Beersheba, Israel, and a lecturer in psychiatry at
Ben Gurion University in Beersheba.
The Genetics of Bad Behavior
Science: A study links violence to heredity
Geoffrey Cowley with Carol Hall
Newsweek, November 1, 1993
They may be the Netherlands’ most
dysfunctional family. One brother raped his
sister; later, in a mental institution, he stabbed a
warden in the chest with a pitchfork. Another
relative tried to run his boss down with a car.
Two others were firebugs, and still another had a
habit of creeping into his sisters’ bedrooms and
forcing them, at knifepoint, to undress.
These folks haven’t been on “Geraldo” yet,
but they have helped validate the notion that
heredity can foster aggression. Writing in the
journal Science last week, Dutch researchers
linked the family’s problems to a single aberrant
gene. “It was always clear that genetics was
involved in behavior,” says Dr. H. Hilger
Ropers, one of the study’s authors. “But this is
the first example showing a specific gene that
changes the behavior of individuals.”
The Dutch researchers have pursued the gene
since 1978, when one of the men’s sisters cane to
the University Hospital in Jijmegen to seek
advice about having children. She described her
family’s problem as mental retardation, not
violent behavior. But when geneticist Han
Brunner started studying the affected men, he
found that low intelligence was not their main
problem. Their IQs were nearly normal, but they
shared a marked inability to control their
impulses. Tracing the family back five
generations, Brunner found 14 men who fit that
profile, but not a single woman. Though no one
yet knew whether the problem was hereditary,
that pattern suggested a possible mode of
transmission. Because men have only one X
chromosome, they’re especially vulnerable to
any defect it contains. (Women, with two X’s,
can carry a defect on one of them without
suffering any effects.” If this syndrome involved
a bad gene, the X chromosome was the obvious
place to look for it.
The researchers started analyzing blood
samples, but because the X chromosome
contains volumes of genetic material, it took
them a decade to find the relevant mutation.
According to the new study, the men’s problems
stem from a tiny defect in the gene that enables
the body to produce an enzyme called MAOA
(monoamine oxidase A). MAOA breaks down
the molecules that transmit signals within the
brain. Because men with the mutation don’t
produce the enzyme, their brains are presumably
flooded with transmitters. No one can say with
certainty that those chemicals provoke the men’s
strange actions, but previous studies have linked
transmitters called serotonin and noradrenaline to
aggressive behavior. And there’s no question
that the affected men fail to break such
substances down. When the researchers studied
17 men from the cursed family, each of the five
with behavioral problems exhibited an MAOA
mutation – and each had unprocessed
neurotransmitters in his urine.
However eye-popping, the new findings
don’t imply that antisocial behavior is a simple
matter of heredity. Obviously, a rare familial
disorder can account for only a small fraction of
the mayhem in the world. Even within the
affected family, inheriting the gene doesn’t
guarantee a life of violent crime. Though all the
known carriers have had problems, some have
fared better than others. At least one carrier has
managed to keep a job and a family. As Ropers
observes, “There are people who feel the urge to
be violent, but are able to control it.” Still, as the
new study makes clear, heredity can skew the
odds against you.