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James Brody
June 23rd, 2005, 08:00 AM
Thanks to Todd Stark and the Paleopsych Lists for alerting me to this!
JB
-----------
Some Politics May Be Etched in the Genes
http://www.nytimes.com/2005/06/21/science/21gene.html

[The article will follow in a moment.]

By [3]BENEDICT CAREY

Political scientists have long held that people's upbringing and
experience determine their political views. A child raised on peace
protests and Bush-loathing generally tracks left as an adult, unless
derailed by some powerful life experience. One reared on tax protests
and a hatred of Kennedys usually lists to the right.

But on the basis of a new study, a team of political scientists is
arguing that people's gut-level reaction to issues like the death
penalty, taxes and abortion is strongly influenced by genetic
inheritance. The new research builds on a series of studies that
indicate that people's general approach to social issues - more
conservative or more progressive - is influenced by genes.

Environmental influences like upbringing, the study suggests, play a
more central role in party affiliation as a Democrat or Republican,
much as they do in affiliation with a sports team.

The report, which appears in the current issue of The American
Political Science Review, the profession's premier journal, uses
genetics to help answer several open questions in political science.

They include why some people defect from the party in which they were
raised and why some political campaigns, like the 2004 presidential
election, turn into verbal blood sport, though polls find little
disparity in most Americans' views on specific issues like gun control
and affirmative action.

The study is the first on genetics to appear in the journal. "I
thought here's something new and different by respected political
scholars that many political scientists never saw before in their
lives," said Dr. Lee Sigelman, editor of the journal and a professor
of political science at George Washington University.

Dr. Sigelman said that in many fields the findings "would create
nothing more than a large yawn," but that "in ours, maybe people will
storm the barricades."

Geneticists who study behavior and personality have known for 30 years
that genes play a large role in people's instinctive emotional
responses to certain issues, their social temperament.

It is not that opinions on specific issues are written into a person's
DNA. Rather, genes prime people to respond cautiously or openly to the
mores of a social group.

Only recently have researchers begun to examine how these
predispositions, in combination with childhood and later life
experiences, shape political behavior.

Dr. Lindon J. Eaves, a professor of human genetics and psychiatry at
Virginia Commonwealth University, said the new research did not add
much to this. Dr. Eaves was not involved in the study but allowed the
researchers to analyze data from a study of twins that he is leading.

Still, he said the findings were plausible, "and the real significance
here is that this paper brings genetics to the attention to a whole
new field and gives it a new way of thinking about social, cultural
and political questions."

In the study, three political scientists - Dr. John Hibbing of the
University of Nebraska, Dr. John R. Alford of Rice University and Dr.
Carolyn L. Funk of Virginia Commonwealth - combed survey data from two
large continuing studies including more than 8,000 sets of twins.

From an extensive battery of surveys on personality traits, religious
beliefs and other psychological factors, the researchers selected 28
questions most relevant to political behavior. The questions asked
people "to please indicate whether or not you agree with each topic,"
or are uncertain on issues like property taxes, capitalism, unions and
X-rated movies. Most of the twins had a mixture of conservative and
progressive views. But over all, they leaned slightly one way or the
other.

The researchers then compared dizygotic or fraternal twins, who, like
any biological siblings, share 50 percent of their genes, with
monozygotic, or identical, twins, who share 100 percent of their
genes.

Calculating how often identical twins agree on an issue and
subtracting the rate at which fraternal twins agree on the same item
provides a rough measure of genes' influence on that attitude. A
shared family environment for twins reared together is assumed.

On school prayer, for example, the identical twins' opinions
correlated at a rate of 0.66, a measure of how often they agreed. The
correlation rate for fraternal twins was 0.46. This translated into a
41 percent contribution from inheritance.

As found in previous studies, attitudes about issues like school
prayer, property taxes and the draft were among the most influenced by
inheritance, the researchers found. Others like modern art and divorce
were less so. And in the twins' overall score, derived from 28
questions, genes accounted for 53 percent of the differences.

But after correcting for the tendency of politically like-minded men
and women to marry each other, the researchers also found that the
twins' self-identification as Republican or Democrat was far more
dependent on environmental factors like upbringing and life experience
than was their social orientation, which the researchers call
ideology. Inheritance accounted for 14 percent of the difference in
party, the researchers found.

"We are measuring two separate things here, ideology and party
affiliation," Dr. Hibbing, the senior author, said.

He added that his research team found the large difference in
heritability between the two "very hard to believe," but that it held
up.

The implications of this difference may be far-reaching, the authors
argue. For years, political scientists tried in vain to learn how
family dynamics like closeness between parents and children or the
importance of politics in a household influenced political ideology.
But the study suggests that an inherited social orientation may
overwhelm the more subtle effects of family dynamics.

A mismatch between an inherited social orientation and a given party
may also explain why some people defect from a party. Many people who
are genetically conservative may be brought up as Democrats, and some
who are genetically more progressive may be raised as Republicans, the
researchers say.

In tracking attitudes over the years, geneticists have found that
social attitudes tend to stabilize in the late teens and early 20's,
when young people begin to fend for themselves.

Some "mismatched" people remain loyal to their family's political
party. But circumstances can override inherited bent. The draft may
look like a good idea until your number is up. The death penalty may
seem barbaric until a loved one is murdered.

Other people whose social orientations are out of line with their
given parties may feel a discomfort that can turn them into opponents
of their former party, Dr. Alford said.

"Zell Miller would be a good example of this," Dr. Alford said,
referring to the former Democratic governor and senator from Georgia
who gave an impassioned speech at the Republican National Convention
last year against the Democrats' nominee, John Kerry.

Support for Democrats among white men has been eroding for years in
the South, Dr. Alford said, and Mr. Miller is remarkable for remaining
nominally a Democrat despite his divergence from the party line on
many issues.

Reached by telephone, Mr. Miller said he did not see it quite that
way. He said that his views had not changed much since his days as a
marine, but that the Democratic Party had moved.

"And I'm not talking about inch by inch, like a glacier," said Mr.
Miller, who makes the case in a new book, "A Deficit of Decency." "I'm
saying the thing got up and flew away."

The idea that certain social issues produce immediate unthinking
reactions comes through in other political research as well. In
several recent studies, Dr. Milton Lodge of the State University of
New York at Stony Brook has shown that certain names and political
concepts - "taxes" or "Clinton," for example - produce almost
instantaneous positive or negative reactions.

These intensely charged political reflexes are shaped partly by
inheritance, Dr. Lodge said.

It may be the clash of visceral, genetically primed social
orientations that gives political debate its current malice and fire,
the study suggests.

Although the two broad genetic types, more conservative and more
progressive, may find some common ground on specific issues, they
represent fundamental differences that go deeper than many people
assume, the new research suggests.

"When people talk about the political debate becoming increasingly
ugly, they often blame talk radio or the people doing the debating,
but they've got it backward," Dr. Alford said. "These genetically
predisposed ideologies are polarized, and that's what makes the debate
so nasty.

"You see it in people's eyes when they talk politics. You can hear it
their voices. After about the third response, we all start sounding
like talk radio on some issues."

The researchers are not optimistic about the future of bipartisan
cooperation or national unity. Because men and women tend to seek
mates with a similar ideology, they say, the two gene pools are
becoming, if anything, more concentrated, not less.
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James Brody
June 23rd, 2005, 08:04 AM
Again, thanks to Todd Stark & the Paleopsych lists for alerting me to this!
JB
-------

Are Political Orientations Genetically Transmitted?
American Political Science Review (2005), 99:2:153-167
JOHN R. ALFORD a1c1, CAROLYN L. FUNK a2c2 and JOHN R. HIBBING a3c3

a1 Rice University
a2 Virginia Commonwealth University
a3 University of Nebraska

Abstract

We test the possibility that political attitudes and behaviors are the result
of both environmental and genetic factors. Employing standard methodological
approaches in behavioral genetics?specifically, comparisons of the differential
correlations of the attitudes of monozygotic twins and dizygotic twins?we
analyze data drawn from a large sample of twins in the United States,
supplemented with findings from twins in Australia. The results indicate that
genetics plays an important role in shaping political attitudes and ideologies
but a more modest role in forming party identification; as such, they call for
finer distinctions in theorizing about the sources of political attitudes. We
conclude by urging political scientists to incorporate genetic influences,
specifically interactions between genetic heritability and social environment,
into models of political attitude formation.


Correspondence:
c1 John R. Alford is Associate Professor, Department of Political Science, Rice
University, Houston, TX 77251 (jra@rice.edu).
c2 Carolyn L. Funk is Associate Professor, L. Douglas Wilder School of
Government and Public Affairs, Virginia Commonwealth University, Richmond, VA
23298 (clfunk@vcu.edu).
c3 John R. Hibbing is Foundation Regents Professor, Department of Political
Science, University of Nebraska?Lincoln, Lincoln, NE 68588 (jhibbing@unl.edu).


List of Figures and Tables

Table 1 - Genetic and Environmental Influences on Political Attitudes: The 28
Individual Wilson?Patterson Items

Table 2 - Genetic and Environmental Influences on Political Attitudes: Summary
Index and Additional Non?Wilson?Patterson Items

Table 3 - Comparison of Australian and U.S. Estimates of Genetic and
Environmental Influences on Political Attitudes

Why do people think and act politically in the manner they do? Despite the
foundational nature of this question, answers are unfortunately incomplete and
unnecessarily tentative, largely because political scientists do not take
seriously the possibility of nonenvironmental influences. The suggestion that
people could be born with political predispositions strikes many as
far-fetched, odd, even perverse. However, researchers in other disciplines?
notably behavioral genetics?have uncovered a substantial heritable component
for many social attitudes and behaviors and it seems unlikely that political
attitudes and behaviors are completely immune from such forces. In this
article, we combine relevant findings in behavioral genetics with our own
analysis of data on a large sample of twins to test the hypothesis that,
contrary to the assumptions embedded in political science research, political
attitudes have genetic as well as environmental causes. 1

Testing this hypothesis is important for two reasons. First and most broadly,
as behavioral scientists we need to analyze all possible shapers of behavior,
not just a select few. Second, a more complete understanding of the sources of
attitudes and behaviors will help us to sort through existing puzzles of
considerable interest to political scientists. One example is political
ideology. Why is a reasonably standard left?right spectrum so widely applicable
cross-culturally and over time? The universal left?right elements of belief
systems around the world and over the decades is difficult for behavioralists
to explain. But if there is a genetic component to political ideologies, if the
constraints on belief systems come not just from intellectualization or
indoctrination but from something deeper, the concept of ideology takes on
greater meaning and the commonality of ideology becomes easier to understand.

ATTITUDE FORMATION

Debates concerning the source of political attitudes revolve primarily around
the question of whether early childhood factors have lasting relevance or
whether these factors tend to be overwhelmed by more proximate events. Survey
responses to political items presumably reflect attitudes and are thought to be
a combination of longstanding ?predispositions? and more recent
?off-the-top-of-the-head? considerations (Zaller 1992, chaps 1?3; also see
Converse 1964 ). Alternatively, an ?on-line? pattern of processing could allow
new incidents to ratchet affect one way or another from previously existing
summary locations (see Lodge, McGraw, and Stroh 1989 ). Regardless, proximate
forces include recent conversations and experiences, question-wording, priming
from previous questions, and a variety of similar factors. Predispositions, on
the other hand, are thought to be a ?distillation of a person's lifetime
experiences, including childhood socialization and direct involvement with the
raw ingredients of policy issues? (Zaller 1992, 23). 2 Great interest exists in
determining the relative clout of the early as opposed to the late environment
but no interest has been displayed in determining the relative clout of
environmental as opposed to genetic variables.

A parallel conclusion applies to research on individual attitudes rather than
survey responses generally. For example, the consensus among those who study
tolerance is that the extent to which individuals are tolerant hinges on a
combination of ?antecedent conditions and contemporary information? (Marcus et
al. 1995 ). Antecedent conditions, in turn, are believed to be shaped by
?personal circumstances? such as ?family, neighborhood, region?and early group
experiences? (Marcus et al. 1995, 5; for more on the importance of long
established proclivities, or antecedent conditions, see Stouffer 1955).
Typically, no role for genetically-induced tendencies is considered (for an
exception, see Monroe 2004, chap 6).

More broadly, the literature on political socialization has long revolved
around the question of the effects of early as opposed to late environmental
forces. Early political socialization researchers (e.g., Easton and Dennis
1969, Greenstein 1960, Jennings and Niemi 1968, and Searing, Schwartz, and Lind
1973) and the authors of The American Voter (Campbell et al. 1960 ) presented
arguments and evidence supporting the primacy of early events. Later
researchers, however, questioned the value of early childhood socialization and
provided evidence that judgments about more recent conditions and occurrences
can dramatically alter preferences we might have held as children and
adolescents (see, e.g., Fiorina 1980; for good summaries of the debate over the
relative importance of early and late environmental events, see Cook 1985;
Merelman 1986, and Sears 1989). In the last 50?60 years, the emphasis in the
literature has gone from personality studies (Adorno et al. 1950; Eysenck 1954;
Laswell 1930 ), to ideological and childhood socialization studies, to the
effects of media frames, perceptions of current conditions, and other types of
contemporary information. In fact, for the past couple of decades research on
political socialization has been suffering through a ?bear market? (Cook 1985
), and studies of personality, while experiencing a remarkable comeback in
psychology (for an introduction, see Wiggins and Trapnell 1997 ), have been
largely absent from political science since McCloskey's (1958) work in the
1950s on the conservative personality. Thus, political science debates
concerning the source of political attitudes and behaviors have been over
timing, over whether attitudes and behaviors are primarily shaped early in life
or by more proximate occurrences. Conspicuously absent is consideration of the
possibility that certain attitudes and behaviors may be at least partially
attributable to genetic factors.

MODERN BEHAVIORAL GENETICS

But what is the physical process by which a genetic allele could shape a
political attitude? If there is any connection at all, is it not that the
effect is so small that it can be safely ignored? And even if this is not the
case, in light of potentially troubling normative implications such as
biological determinism, is it not best to ignore relationships between genes
and social behavior? It is difficult for many outside the biological sciences
to understand how it is even possible for genes to influence behavior, so a
brief discussion is in order. Genes provide instructions for the production of
proteins, which are built and identified by a specific combination of amino
acids (which in turn are constructed from complex organic molecules). As such,
each protein has a chemical sequence that then interacts with other chemicals
in the body, sometimes reacting directly with these other chemicals but often
serving as enzymes that facilitate but are not themselves altered by chemical
reactions. If a gene coding for a particular enzyme is absent, the chemical
reaction it is meant to enhance will occur with much less efficiency. For
example, a gene for the enzyme tryptophan hydroxylase-2 (Tph2) facilitates
production of the neurotransmitter serotonin in the brain, but a certain form
of this gene (which varies from the standard form by a single amino acid)
produces about 80% less serotonin and people with this mutant allele appear to
be significantly more likely to suffer from unipolar depression (Zhang et al.
2005).

Still, the connection is rarely so simple that a given genetic allele can be
seen as causing a certain behavior. More typically, findings in modern
behavioral genetics reveal the effect of genes to be interactive rather than
direct, let alone determinative. To provide one illustration, in humans there
is a gene on chromosome 17 involved with serotonin reuptake (5-HTT). As is
often the case with genes, 5-HTT has a long allele and a short allele. Mice
have a parallel gene, and in that species the short form had previously been
connected to listless, depressive behavior. Scientists were eager to determine
if such a correlation between the short form of 5-HTT and depression was
present in humans. In a long-term study of the health records of nearly 1,000
New Zealanders whose 5-HTT alleles were known, it was found that major episodes
of depressive behavior were not much more prevalent among those with the short
form. But then the researchers combined genetics and the environment;
specifically, they interacted each subject's 5-HTT allele with the number of
high-stress events (romantic calamities, bankruptcies, deaths of loved ones,
etc.) experienced in that individual's life. They found that those who had a
high number of such events and who had the short form of 5-HTT were
significantly more likely to display behaviors associated with depression
compared to either those experiencing few high stress events or those with the
long form who suffered through a comparably large number of high-stress events
(see Caspi et al. 2003).

In this particular case, genotype did not make people behave a certain way;
rather, it influenced the extent to which their behavior was contingent on the
environment?and this pattern likely will apply to all sorts of other human
activities. Whether the behavior of interest is depression, cooperation, fear
response, or susceptibility to drug addiction, some people are more sensitive
than others to particular features of their environment, and genetics, far from
determining behavior, influences its sensitivity. Genetics makes the mood of
some people far more dependent on the extent to which their lives have been
beset with difficulties and it likely makes some people's political attitudes
far more contextually dependent than others. In other words, the connection
between genes and attitudes may not involve specific attitudes as much as the
flexibility of those attitudes (Is abortion always wrong, or does it depend?).
The issue is not nature versus nurture but the manner in which nature interacts
with nurture (see Marcus 2004 and Ridley 2003).

MONOZYGOTIC AND DIZYGOTIC TWINS

The process of identifying in the laboratory the precise genes responsible for
given human behaviors (especially those behaviors that do not have corollaries
in lab-friendly animals such as mice) is extremely challenging. Fortunately,
even without identifying the genes responsible, it is possible to compile
information on the matter of most concern to social scientists: the extent to
which attitudes and behaviors have a genetic component. The relevant procedures
center on comparisons of monozygotic (MZ; frequently but erroneously called
identical) twins and dizygotic (DZ; fraternal) twins.

MZ twins develop from a single egg, fertilized by a single sperm, and share an
identical genetic inheritance. DZ twins develop from two separate eggs,
fertilized by two separate sperm, and are in effect simply two siblings that
happen to be born simultaneously. As such, DZ twins share the same average of
50% of genetic material as do any two biological siblings. It is this fixed
ratio (two to one) of genetic similarity between MZ and DZ twins, and the
contrasting average equivalence of environment influence, that provides most of
the power of twin designs. It is important to appreciate that the assumption of
environmental equivalence is one of equivalence across types of twins, not
across pairs of twins or across twins within a given pair. For example, there
is undoubtedly at least some variability in parental socialization across
siblings, even those of identical age, but across multiple twin pairs the
assumption is that this variability is essentially equal for the MZ and the DZ
pairs.

This assertion that the effect of genetics is measurably distinct for MZ and DZ
twins, while the effect of the environment is either equivalent or at least
randomly distributed around equivalence, is crucial to everything that follows
from twin research. It is important therefore to raise and consider the
criticisms of this fundamental assumption. The arguments come in two essential
varieties. The first is that MZ twins, genetics aside, experience a more
similar environment because they are treated more similarly than are DZ twins.
This would seem particularly telling for childhood socialization, where, for
example, parents might show less of a tendency to treat MZ twins as individuals
compared to DZ twins. The second is that MZ twins, genetics aside, interact
with each other more throughout life than do DZ twins. This would seem to be of
particular importance for adult socialization, where closer adult contact
between MZ twins might lead us to expect a greater degree of environmentally
induced similarity than we would see for the more distant DZ twins.

Both caveats have been subject to sustained and varied investigation and
neither has been found to hold up under empirical scrutiny. The argument of
more similar treatment fails on several fronts. Parents frequently
miscategorize their twins (DZ twins are often believed by their parents to be
MZ twins) and the differential correlation persists in these instances of
miscategorization. In other words, the degree of correspondence between MZ
twins surpasses that of DZ twins even in the large subpopulation of twins
thought by their parents to be MZ twins (Bouchard and McGue 2003; Bouchard et
al. 1990; Plomin 1990 ). The contention that MZ twins have closer or more
frequent contact than DZ twins turns out to be at best irrelevant. The
correlation between the frequency of contact between twins and the similarity
between twins on all attitudinal and behavioral variables tested, including
conservatism, is slight and actually negative (Martin et al. 1986 ). In other
words, twins in greater contact with their cotwins are not more likely to share
the same attitudes and behaviors, so even if MZ twins have more contact than DZ
twins, this contact is not the cause of any elevated correlations. But the most
powerful refutation of both of these criticisms comes in recent studies
utilizing MZ and DZ twins raised apart. These studies uniformly validate MZ and
DZ differences found in earlier studies of twins raised together. Arguments
about the relative degree of shared environmental effects between MZ and DZ
twins simply offer no credible explanation if the twins in question have been
raised apart (Bouchard 1998; Bouchard et al. 1990 ). In effect, this naturally
occurring, if uncommon, condition provides precisely the sort of laboratory
control that we would want in an experimental setting. 3

Other evidence against the exclusive environmental argument is that the
empirical results suggest MZ twins reared together are often less likely to
share behavioral traits with their twins than are MZ twins reared apart,
presumably because of extra efforts to establish distinct identities when the
twins live together. In addition, as adult MZ twins living apart age, they tend
to become more, not less, similar (Bouchard and McGue 2003 ), a finding that is
difficult to reconcile with the belief that only the environment matters.
Interestingly, this precise effect is predicted in an early landmark criticism
of behaviorism and the conditioned response research on animal behavior that
formed its empirical core. Over time, substantial anomalies began to accumulate
in this research pointing toward a primacy for some nonenvironmental behaviors.
Breland and Breland (1961) summarized this tendency with the phrase ?learned
behavior drifts toward instinctive behavior? (684).

Given the genetic differences and environmental similarities of the two types
of twins, for any trait that is partly heritable the tendency for MZ twins to
share that characteristic should be stronger than the tendency for DZ twins to
share that characteristic. In contrast, characteristics that arise purely from
the environment, whether shared by the twins, as would typically be the case
for parental socialization, or not shared by the twins, as would be the case
for many adult experiences, should not generate any significantly different
patterns when we contrast MZ and DZ twins (see Eaves, Eysenck, and Martin 1989
and Plomin et al. 2001 for a thorough discussion of the relevant statistical
techniques).

The procedures involved with the twin methodology are standard fare in
behavioral genetics but are not familiar to most political scientists, so it is
appropriate that we explain the basic terminology, theory, and technique in
some detail. Influences on an individual trait, whether it is a political
attitude or a physical characteristic, are typically divided into two broad
groups?heredity (H) and environment (E). The total variation in a trait can
thus be represented as the sum H + E. Heredity is the impact of genetic
inheritance on trait variation. In the case of a physical characteristic such
as adult height, this would be the proportion of the total variation in height
across individuals due to the variation across individuals in the multiple
genes that control ultimate physical height. For any one individual, the source
of this genetic influence is relatively well defined, as on average 50% of our
genes come from our mother and 50% come from our father. This leads to the fact
that biological children of tall parents are more likely to be tall than are
the biological children of short parents, though even for a relatively
straightforward additive physical trait like height, the relationship is far
from determinative.

?Environment? is all of the nongenetic external factors that influence trait
variation across a population. These influences range broadly from the earliest
biological environment of the womb, to the physical environment of a childhood
house, to the social environment of the adult workplace. In the case of adult
height, some of the obvious environmental factors are prenatal nutrition, the
adequacy of childhood and adolescent diet, and exposure to chemical agents that
can inhibit growth.

Environmental influences can be further divided into two subcategories: the
shared environment and the unshared, or unique, environment. The shared
environment is all of the shared external influences that we would typically
think of as leading to trait similarity between individuals. Siblings, for
example, might share similar childhood environments, including similar parental
interactions, a similar physical environment, and similar nutrition. If the
siblings happen to be twins, they would also share a more similar prenatal
environment. 4 In the case of adult height, a shared environmental factor, such
as a regional diet limited in protein and specific nutrients, could lead to
similarity in height across the entire population of a region.

The unshared environment is all of the distinctive external influences that we
would typically think of as leading to trait dissimilarity across individuals.
While much of the early childhood environment, for example, is similar across
siblings, much is nonetheless variable. Siblings differ in diet, disease
exposure, peer influences, and a host of other unique experiences. Even twins,
whose childhood environment is made increasingly similar by virtue of their
identical age, are exposed to substantial unique external influences. With the
shift to adult life, the share of unique influences on siblings increases
sharply, as peer, workplace, family, and physical settings typically diverge.

In the classic political science studies of socialization (see, especially,
Jennings and Niemi 1968, 1991 and Tedin 1974 ), the focus has been on the
correlation between the attitudes of parents and their children. In terms of
the three sources of trait variability outlined above, as informative as it is,
this design does not allow for an unambiguous estimation of any of the three
categories. The correlation between a parent and a child arises from a
combination of shared genes, shared environment, and parental socialization (an
indirect form of shared environment in which the parent's attitudes provide a
path from the parent's environment to the child's environment), all of which
are pressures toward similarity in parent?child attitudes. The failure of this
parent?child correspondence to reach +1.0 presumably reflects the pressure
toward dissimilarity coming from the unshared environment, but since the
genetic similarity of a parent?offspring pair is only .5, there is as much
genetic dissimilarity as there is similarity. Thus, trait dissimilarity, like
trait similarity, is an undetermined mixture of genetic and environmental
influences. Our inability to tease apart genetic heritability and environment,
whether shared or unshared, in these parent?child studies is a direct result of
the fact that there is no measured variation in genetic similarity across the
data set of parent?child pairs (i.e., all biological offspring share the same
average of 50% of the variable genetic code with each parent).

This inability of standard parent?child observations to distinguish genetic
heritability from parental socialization (or other features of the shared
environment) is something that has long been understood, but largely ignored in
modern social science. Fortunately, twins provide a powerful ?natural
experiment? by introducing known genetic variation into analyses of the sources
of trait variability. By shifting the focus from the similarity between parents
and offspring to the similarity between two siblings, we can take advantage of
the fact that some siblings vary in well-known ways in the degree of their
genetic correlation.

POLITICS AND GENETICS: PREVIOUS FINDINGS AND OUR EXPECTATIONS

Comparisons of the correlations of MZ and DZ twins on a wide variety of
variables have been conducted, with intriguing results. Using appropriate
modeling techniques including controls for parental traits and assortative
mating, it is possible to partition the explanatory powers of heredity, shared
environment, and nonshared environment on any given variable. These techniques
have been valuable for epidemiological traits, intelligence, personality,
social attitudes such as those connected to religion, psychological interests,
and behaviors such as risk-taking propensities (for a thorough review, see
Bouchard and McGue 2003 ). Of most interest to us are the findings pertaining
to social attitudes and behaviors. At first, researchers were so confident that
social attitudes were not heritable that they employed such items as controls.
Quickly they discovered that other controls would have to be found because most
social attitudes consistently displayed a surprising measure of heritability
(see, e.g., Crelia and Tesser 1996, Scarr and Weinberg 1981, and Tesser 1993).

Political attitudes were never a central focus in this research stream but many
of the patterns found in other social attitudes should be present for political
attitudes as well, and this assumption guided the formulation of our
expectations. Since the social attitudes tested to date have demonstrated a
strong heritable component, frequently stronger than attitude covariance
attributable to shared environment, we predict that political attitudes will
also be heavily heritable. Heritability estimates calculated by previous
researchers for attitudes associated with psychological conservatism are quite
high, while the relevant models typically show little or no effect for shared
environment (the remainder is likely the result of nonshared environmental
factors). Notably, these findings come from studies of twins in settings as
disparate as Australia, Virginia, and Minnesota, and the findings of the
Minnesota study, utilizing twins reared apart, conform well to the other
studies of twins raised together (for a summary, see Bouchard and McGue 2003).
5 Careful studies of adopted children confirm the finding that genetics matter
more than parentally created environment in influencing social attitudes and
behaviors, personality traits, and intelligence. 6

We further predict that attitudes on political issues tracking most closely to
central personality traits should be the most heritable since personality
traits are generally heritable and since the heritability of social attitudes
is likely derivative of the heritability of various personality traits (see
Bouchard and Loehlin 2001 and Eaves, Eysenck, and Martin 1989 ). For example,
one of psychology's ?Big 5? personality traits is general ?openness? and it
seems likely degree of openness is relevant to the political arena as well.
Liberals and conservatives, on average, differ in their openness to atheism,
homosexuality, communism, immigration, and countercultural activities. These
differences may be entirely due to enculturation, but then again, they may not
be, and we will never know without testing for the effects of genetics.

Based on behavioral geneticists' study of religion, it seems that group
identification is something that is heavily influenced by the environment,
especially shared environment, and is mostly unconnected to genetics. Children
of Methodists are likely to be Methodists not because there is a gene for
Methodism or even a personality particularly oriented toward Methodism, but
because of parental socialization. Thus, even as attitudes connected to
religiosity and religious beliefs and activities (e.g., Sabbath observance,
church authority, belief in heaven, religious fundamentalism, frequency of
attendance) were found to be shaped more by genetic inheritance than by
parental views on those issues (for details, see Bouchard et al. 1999, Eaves,
Martin, and Heath 1990, Maes et al. 1999, and Martin et al. 1999 ),
identification with a particular religious group was shaped more by
socialization and almost not at all by genetics. We expect to find a similar
pattern with political party identification. Children are eager to belong to
the groups their parents belong to and parents are frequently eager to
encourage children in this regard. Assuming these identifications have some
stickiness into early adulthood, our core expectation is that party
identification will be influenced more by parental socialization (shared
environment) than by genetic inheritance but that this pattern will be reversed
for political attitudes with inheritance playing a role at least as large as
the shared environment. By predicting a large influence for genetic
inheritance, we depart from typical behavioralist expectations anticipating
that political attitudes will be predominantly influenced by environmental
factors, rendering genetic inheritance largely, if not completely,
inconsequential.

DATA AND METHODS

Since twin studies have not been conducted by political scientists, political
attitudes have been at best a sidelight, and properly refined measures of
political variables have not been constructed and employed (the heritability of
political behavior has not been analyzed at all). Nonetheless, some previously
employed variables in twin studies have political relevance. For example, the
heritability of conservatism is frequently assessed (see, e.g., Bouchard et al.
1990, Eaves, Eysenck, and Martin, 1989, and Martin et al. 1986 ), and even
though conservatism is viewed by the scholars who do twin studies more as a
psychological trait than a political ideology, measures of it include political
items.

Of most relevance here is the Wilson?Patterson (W?P) Attitude Inventory. This
inventory is administered by presenting subjects with a short stimulus phrase
such as death penalty or royalty and eliciting a simple agree, disagree, or
uncertain response. The broadest version of the W?P inventory includes 50
items, 25 of which contribute positively to the conservatism score and 25 of
which contribute negatively to the conservatism score. While some of the items
relate to a heavily social conception of conservatism?for example, pajama
parties, nudist camps, computer music, and horoscopes?others have a much more
direct political content?for example, disarmament, socialism, patriotism, and
death penalty. Studies typically utilize reduced sets of W?P items or modify
individual items to better suit the country in which the items are being
administered. For political science this presents two frustrations. The list of
politically relevant items is tantalizing but limited and unfocused, and the
results are often presented only for the entire combined scale, making it
difficult to assess the contribution of the directly political items to the
overall index of heritability.

We were granted access to the data for the W?P items in the United States and
were able to conduct comparable, though more limited, twin correlation analyses
from published results of an Australian study. 7 The U.S. study included
information on thousands of twin pairs in Virginia, supplemented with twin
pairs recruited through the cooperation of AARP. A subset of these twins and
their relatives has been asked questions regarding their social attitudes,
including numerous items from the W?P inventory.

A brief explication of twin methodology should help readers make independent
sense of the tables. The standard techniques in behavioral genetics are based
on correlation analysis (in the case of limited response items like the W?P
inventory, the actual measure is the polychoric correlation coefficient, a
technique that is appropriate when individual subjects are using a limited set
of categories to express location on what is in fact a continuous trait). The
correlations are computed separately for male/male and female/female twin pairs
to provide an appropriate comparison, since all MZ twins are same-sex pairs,
while DZ twins are a mix of same-sex and opposite-sex pairs (in other words,
female/male DZ twin pairs are excluded from the analysis). Without this
control, the presence of any male/female differences would spuriously deflate
the correlations for DZ pairs relative to the same-sex MZ pairs.

Heritability is typically estimated by subtracting the correlation for DZ pairs
from the correlation for MZ pairs and then doubling the resulting difference.
At one extreme, if the correlations are the same for MZ and DZ pairs,
suggesting that genetic similarity plays no role in similarity for that
particular trait, then the result will be an estimate of heritability of zero.
At the other extreme, a purely genetic additive trait should produce a
correlation of .5 for DZ pairs and 1.0 for MZ pairs, resulting in an estimate
of heritability of 1.0 (1.0 - .5 = .5, and 2 * .5 = 1.0). In a similar way, we
can estimate the influence of shared environment, as opposed to shared genetic
material, by doubling the correlation for DZ pairs and then subtracting the
correlation for MZ pairs. Again, a purely genetic additive trait should produce
a correlation of .5 for DZ pairs and 1.0 for MZ pairs, resulting in an estimate
of the impact of shared environment of zero (2 * .5 = 1.0, and 1.0 - 1.0 = 0).
At the other extreme, if the correlations are the same for MZ and DZ pairs,
suggesting that genetic similarity plays no role in similarity for that
particular trait, then the result will be an estimate of the impact of shared
environment that is equal to the MZ or DZ correlation (e.g., if MZ = DZ = .4,
then 2 * .4 = .8, and .8 - .4 = .4). Whatever is left over is taken to be
attributable to the unshared environment.

THE HERITABILITY OF POLITICAL ATTITUDES

Table 1 contains the results of a standard polychoric correlation analysis for
the 28 W?P items available in the Virginia 30K data set and for a select set of
additional items to provide some sense of perspective for the level of these
correlations. Even the quickest glance at the results in Table 1 is enough to
set aside the traditional view that genes do not play any role in explaining
political attitudes. All 28 of the MZ correlations are larger than their
corresponding DZ correlations, and in every case the difference is
statistically significant at the .01 level. Far from typically being at or near
zero, none of the 28 heritability estimates falls in the single digit range,
and more than half of the 28 items have heritability estimates of .3 or more.
Heritability ranges from a high of .41 to a low of .18, all suggesting that the
influence of heredity on political attitudes is very real, and given the
diverse range of items included here, this genetic influence is also pervasive.
So the view that heritability of social and political attitudes will be nonzero
but small relative to shared environment is also called into question. We see
from Table 1 that the impact of shared environment exceeds that of heredity for
only four of the 28 items, and the mean estimate of heritability for the 28 W?P
items is .32, compared to a mean estimate of shared environmental influence of
.16.

- Genetic and Environmental Influences on Political Attitudes: The 28
Individual Wilson?Patterson Items
<http://journals.cambridge.org/fulltext_content/PSR/PSR99_02/S0003055405051579tbl001.gif>

The second-to-last column in Table 1 reports the estimates for the proportion
of the variation in an attitude that is attributable to the unshared
environment. As described above this is essentially a residual variance
category, reflecting such factors as random choice as well as external
influences such as the unique experience of each individual, including those
from childhood, and later influences in life that have been termed ?adult
socialization? in the political science literature. Across the 28 W?P items the
estimate of the impact of unshared environment varies from about one-third (for
School Prayer) up to about two-thirds (for Pacifism) of the overall variation.
The average impact of the unshared environment for these items is .53, or
roughly half of the overall variation. The summary picture for this set of
political attitudes, then, is that shared influences (genetic and
environmental) account for about half of the variation in these political
reactions, with unique individual and environmental factors accounting for the
remainder. Within the half that is accounted for by shared influences, genetic
influences, in contradiction to behavioralist expectations, are roughly twice
as influential as environmental influences.

While the individual items provide interesting variation, the purpose of the
W?P inventory is to provide an overall index of conservatism. We compute a
simple index by assigning a value of +1 to any ?conservative? response (i.e., a
?yes? to an item like Death Penalty or a ?no? to an item like Women's
Liberation) and [minus sign]1 to any ?liberal? response (i.e., a ?no? to an
item like Death Penalty or a ?yes? to an item like Women's Liberation). Items
where the respondent chose a non-commital (?) response are coded as zero. When
these individual scores are summed across the 28 items they yield an index that
varies from a potential low of [minus sign]28 (indicating a set of uniformly
?liberal? responses) to a high of +28 (indicating a set of uniformly
?conservative? responses). The actual index scores for the twins in the study
range from [minus sign]26 to +26, with the median response falling between +2
and +3. Given the far more continuous nature of this overall index, we can now
utilize the more traditional Pearson's correlation coefficient. The results for
the overall index are presented in Table 2 and clearly support a powerful role
for heredity in influencing conservatism, at least as measured by the W?P
inventory. The estimate for heritability is .43, higher than for any of the
individual items. The estimate for shared environment is .22, falling within
the upper range of the individual items, while the estimate for unshared
environment is only .35, falling very near the bottom of the range for
individual items. The overall picture is again a very strong role for heredity
and a less powerful, but clear role for shared environment. What is different
for the overall index is that the role of shared influences (genetic and
environmental) account for almost two-thirds of the variation in the index
(compared to about one-half for the individual items), with unique individual
and environmental factors accounting for only about one-third of the variation.
This decline in the role of unique individual and environmental factors seems
sensible, as we are moving from individual and highly specific items that could
involve a host of unique experiential, associational, and informational
perturbations to an index where those idiosyncratic features of individual
items have the opportunity to cancel each other out.

- Genetic and Environmental Influences on Political Attitudes: Summary Index
and Additional Non?Wilson?Patterson Items
<http://journals.cambridge.org/fulltext_content/PSR/PSR99_02/S0003055405051579tbl002.gif>

The W?P items can also be used to construct a rough index of political
opinionation by taking advantage of the frequency of ? responses. The number of
times that a respondent chose a yes or no response over a neutral ? response
was summed to produce an index that varies from zero to 28, with a 28
indicating that the respondent was willing to express a directional opinion on
all 28 items and a score of zero indicating that the respondent was unwilling
to offer a directional opinion on any of the 28 items. The median for this
index is 21 yes or no response choices of 28 possible. The results for the
overall index clearly support a powerful role for heredity in influencing
political opinionation, at least as it is captured by the admitted rough gauge
of the frequency of nonneutral responses to the W?P inventory items. The
estimate for heritability is .36 and the estimate for shared environment is
only .02. The estimate for unshared environment is high, at .61, falling near
the top of the range for individual items. To the extent that there is a family
effect on political opinionation, it would appear to be entirely a genetic one,
with the remaining roughly two-thirds of the variation being due to nonshared
factors.

Two items from the survey that are not a part of the W?P inventory are included
in Table 2 . Party affiliation is the most clearly political of the items in
the broader questionnaire, and it is useful here on its own, as well as in
contrast to the attitudinal items. Party identification is distinct among U.S.
political attitudes both in our conception of it as an identification, and
hence as something at least potentially distinct from simple item evaluation,
and in its established tendency to correlate well between parent and child (see
Jennings and Niemi 1968). This distinctiveness is apparent in Table 2 . As we
expected, the pattern for party identification is nearly the exact reverse of
that for the average attitude item. Heritability for party affiliation is
relatively low (r = .14), while shared environment is much stronger (r = .41).
Note also that not one of the 28 W?P items has an average heritability that is
as low as that for party affiliation, and likewise, not one of the 28 items has
an average coefficient for the impact of shared environment that is as high as
that for party affiliation. Clearly, party identification is, at least for the
United States, a different sort of beast than reactions to issue items.

In this regard it is particularly interesting that the two major parties also
appear in the W?P battery, but here they are objects of affect rather than
labels of possible identification, and the ?pro? or ?con? reactions to the
parties that these items pick up do not exhibit the same patterns of genetic
and environmental influence that we see for party affiliation. In fact, if we
average the polychoric correlation for the ?Democrats? item with the
correlations for the ?Republicans? item and compute the resulting estimates we
get a heritability estimate of .31 and a shared environment estimate of .17,
almost exactly the same as the mean results for all 28 attitude items. It would
appear that affect toward the major parties is largely a matter of genetic
predisposition but that, just as the political socialization literature has
concluded all along, party identification itself is primarily the result of
parental socialization. This pattern is intriguing in and of itself but it also
should give pause to those who would dismiss the findings on attitude items as
the product of some methodological quirk of twin studies. If estimates of
heritability are somehow artificially inflated, why does this alleged
contamination not occur for party identification?

Table 2 also reports the results for a summary indicator of educational
attainment from the survey. We include it here partly because it reflects an
actual behavior, if only a self-reported one, and partly because it carries the
role of genetics more directly into the world of actual and meaningful social
variation. Educational attainment is also useful as an example of a behavior
that is traditionally thought to be heavily influenced by shared environment,
particularly by parental example, expectations, and resources. This traditional
view is supported by the shared environment estimate of .46, a figure higher
than any of the estimates for the 28 attitude items and even somewhat higher
than the estimate for party ID. What may surprise readers is that as important
as shared environment is to educational attainment, heredity, at .40, is almost
as important. Taken together, family effects are almost the entire story for
variation in education attainment. The estimate for the impact of the unshared
environment is only .14, a value markedly lower than any other in the table.

ASSORTATIVE MATING

Assortative mating is a particular concern here. As detailed above, the
assumption that DZ twins, like any other pair of biological siblings, share on
average 50% of the variable genetic code is crucial to the estimation of
heritability. This contrasts with MZ twins, where the shared proportion is
100%, and the DZ level forms the baseline for separating genetics from the
shared environment. What may not be immediately apparent is that the assumption
that purely genetic traits in DZ twins will on average correlate at .50 is
itself built on the assumption that their biological parents will on average
correlate at .00 for the same traits. In other words, the assumption is that
the parents are not related to each other in any close degree, and this is
typically true, as close relatives generally do not mate, and the amount of
average shared genetic code drops geometrically as we move away in relatedness
and quickly approaches zero. This assumption that mates are genetically
uncorrelated on the trait of interest is, however, violated if mate choice is
itself based on the trait of interest. If, for example, parents have identical
genetic codes for a trait of interest, then the shuffling of that genetic code
produced by sexual reproduction will not result in any variation among DZ
twins, or any other siblings, with regard to their genotype for that trait. In
other words, DZ twins of these parents will be as genetically alike on this one
trait as MZ twins are on this trait. Across a study population, the higher the
proportion of spouses that share identical genetics for a trait, the closer the
DZ correlation will be to the MZ correlation. Since heritability of a trait is
estimated as 2 * (MZ - DZ), the increased similarity of DZ and MZ pairs will
lead to an underestimation of heritability for this genetic trait.

This is important for our assessment of the heritability of political
attitudes. If there is a tendency for people to choose mates with similar
positions on political issues, then the estimates of heritability in Tables 1
and 2 are biased. Fortunately for us, the direction of the bias is uniform and
conservative. Any measurable tendency toward assortative mating on political
orientation will push up the DZ twin correlation while leaving the MZ
correlation unaffected, and this reduction in the MZ?DZ gap will have the
related effect of lowering estimates of heritability. Note also that any
increase in similarity of DZ twins will inflate the estimate of the importance
of shared environment, as the estimation formula of (2 * DZ) [minus sign] MZ
makes clear.

The immediate empirical question is how much of a role assortative mating plays
in political issue positions. A quick answer can be found by looking at the
interspouse polychoric correlations for the individuals included in the
Virginia 30K study. The average inter-spouse polychoric correlation for the 28
items is .41 and the individual correlations range from a low of .26 for
Censorship to a high of .64 for School Prayer. While some of this interspouse
similarity could plausibly be attributed to persuasion effects taking place
after mate choice rather than to assortative mating, the levels of similarity
are probably too high to dismiss assortative mating entirely. This is confirmed
by a preliminary look at the impact of controlling for assortative mating on
these 28 attitude items. The Virginia 30K study includes data for parents of
twins in the study, including parents' individual responses to the same W?P
items that the twins responded to. The usable sample size does drop
substantially when we restrict our analysis to only twin pairs with completed
W?P results for both parents (there are a total of 304 pairs of male/male or
female/female twins with complete twin and parent W?P data, compared to
approximately 4,400 pairs in the twin only analysis in Table 1 ). This
effectively limits us to an assortative mating analysis that focuses on the
overall index score, rather than looking at each item in the inventory
individually.

The approach we used is to compute the partial correlation for twin similarity
in the overall index for the 28 W?P items, controlling for (partialing out) the
influence of the degree of parental similarity on the overall index. The
implication for relative twin agreement is simple; if parental agreement
results from assortative mating, then the resulting increase in genetic
similarity will increase DZ twin correlations (the more alike genetically the
parents are on a trait, the more alike siblings will be on a trait).
Controlling for parental similarity will therefore reduce the size of the DZ
twin correlations. However, parental agreement resulting from assortative
mating and the resulting increase in genetic similarity will not increase MZ
twin correlations (MZ twins are already genetically identical, regardless of
parental similarity or dissimilarity). Therefore, controlling for parental
similarity should have no effect on the size of the MZ twin correlations. In
contrast, if parental agreement results from persuasion or from a shared
environment for the couple, then the impact of parental agreement has no
genetic implications and operates on their offspring solely through its
influence on the offsprings' shared environment. This should produce relatively
higher correlations of equal magnitude for both MZ and DZ twins and, therefore,
lead to roughly comparable reductions in both the MZ and the DZ correlations
when we partial out the effect of parental agreement.

The results for a partial correlation analysis controlling for parental
agreement are reported in Table 2 , on the row just below the results for the
overall index. For MZ twins the issue of whether their parents agree or
disagree on a particular item makes little difference (.65 without control
versus .64 after partialing out the effect of parental agreement). In contrast,
the correlation between DZ twins decreases modestly when the impact of parental
agreement is removed (.43 without control versus .37 after partialing out the
effect of parental agreement). Further, the tendency of assortative mating to
deflate estimates of heritability while inflating estimates of the impact of
shared environment is clear. Without controls, the estimate of heritability for
the overall index is .43 and the average estimate of the impact of shared
environment is .22. When the impact of parental agreement is partialed out, the
average estimate of heritability rises to .53, and the average estimate of the
impact of shared environment drops to .11. Note that the traditional
socialization account of attitude formation is not at odds with this last
finding. If the issue positions of parents are in conflict, then we would
hardly expect this shared conflicted setting to yield sibling agreement. 8

COMPARATIVE POLITICAL GENETICS: EVIDENCE FROM AUSTRALIA

Even with a data set as large as the Virginia 30K, questions may arise over the
extent to which conclusions are bound by time and geography. As a result, it is
helpful to note results from a quite different context and a slightly different
time period. Table 3 presents a comparison of the key summary results in Table
1 from the Virginia 30K study to comparable results in the Australian data
described before (Truett et al. 1994; see also Lake et al. 2000 ). While the
Australian study utilized a larger set of W?P items (50 in all, compared to 28
in the U.S. study), the items were a mix of political and social items, and
only six items appeared in exactly the same form in both studies. An additional
six items were similar enough, in our judgment, to merit comparison, and they
are included in Table 2 with the Australian wording italicized.

- Comparison of Australian and U.S. Estimates of Genetic and Environmental
Influences on Political Attitudes
<http://journals.cambridge.org/fulltext_content/PSR/PSR99_02/S0003055405051579tbl003.gif>

The broad picture from Table 3, and its comparison to Tables 1 and 2 , is one
of remarkable similarity. The mean heritability for the 12 item subset of the
Virginia 30K data is .32 for the full 28 items in Table 1 and .31 for the
12-item subset of the Australian data. The mean estimate for the effect of
shared environment for the 12 item subset of the Virginia 30K data is .12
compared to .16 for the full 28 items in Table 1 and .16 for the 12-item subset
of the Australian data. Thus the general pattern of a relatively greater role
for heredity compared to shared environment detailed above in the discussion of
the U.S. data in Tables 1 and 2 also applies to the Australian data in Table 3
. While most of the individual items also have broadly comparable results in
the two countries, a few, specifically ?socialism? and ?immigration? (?nonwhite
immigration? in the Australian study), are noticeably different. In both cases
the U.S. pattern of substantially higher relative heritability is reversed in
the Australian data, where we see evidence of relatively higher shared
environmental effects. Whether these are meaningful reflections of differences
in how these items relate to deeper political orientations is not clear, but
they are in any case the exceptions rather than the rule. 9

THE GENETICS OF POLITICAL IDEOLOGY

The possibility that attitudes and behaviors are influenced by genetic
variables is an emotionally charged topic so it is important that readers
understand the claims being made. Partitioning the origins of human traits,
whether they be physiological or behavioral, into the discrete, quantifiable
components of genetic inheritance, shared environment, and unshared environment
should not be taken to imply that these components work separately. Rather
these numbers only provide a rough indication of the influence of three
categories of independent variables that are intimately intertwined. (Moreover,
they are estimates of the ability of independent variables to account for
variance in the dependent variables not for the variables themselves.) As
mentioned earlier, gene?culture interaction is the key to understanding the
source of political attitudes and behaviors, just as it is the key to
understanding most physical and behavioral aspects of the human condition.
Genes do not work in isolation and instead generally influence the extent to
which organisms are responsive to particular environmental conditions (see Boyd
and Richerson 1985 and Masters 1993).

And this conditioning influence of genetics on complex social behaviors is not
the product of a single gene but rather numerous genes that, to make matters
more complicated, appear to combine in configural as opposed to additive ways.
The same set of multiple genes may influence behavior in different ways
depending on the order in which they express themselves and the manner in which
they interact with other genes. Recent discoveries also suggest that biological
markers of phenotypic manifestations include the manner in which DNA is packed
in the nucleus, particularly the physical location of genes relative to other
genes and to the histones that help to give DNA its structure. An accurate
understanding of gene expression appears to require knowledge not just of the
sequence of nucleotides (e.g., ATCAGG) that constitutes the gene itself but
also of the context in which each gene resides, thus forming an interesting
parallel to the way we must try to understand the organisms (e.g., human
beings) genes help to construct (for a good summary, see Kosack and Groudine
2004; also see Lykken 1999).

Individual genes for behaviors do not exist and no one denies that humans have
the capacity to act against genetic predispositions. But predictably dissimilar
correlations of social and political attitudes among people with greater and
lesser shared genotypes suggest that behaviors are often shaped by forces of
which the actors themselves are not consciously aware, a point that is made
with some force by Bargh and Chartrand (1999), Marcus (2002), Marcus, Neuman,
and MacKuen (2000), McDermott (2004), and Wegner (2002 ). It is not biological
determinism to posit the existence of complex collections of genes that
increase the probability that certain people will display heightened or
deadened response patterns to given environmental cues. And it is not
antibehavioralism to suggest that true explanations of the source of political
attitudes and behaviors will be found when we combine our currently detailed
understanding of environmental forces with a recognition that genetic variables
subtly but importantly condition human responses to environmental stimuli.

IMPLICATIONS FOR POLITICS

It is important to note that none of the data or arguments presented in this
paper indicates that extant empirical knowledge about political socialization
is useless. In fact, it strongly reinforces many of the most salient findings
in that research stream. We know from that research, for example, that if both
parents share a political identification, there is a high degree of likelihood
that their offspring will have that same political identification (Jennings and
Niemi 1968; Tedin 1974 ). Our ?twin study? results confirm this finding. One of
the peculiar findings in the political socialization literature even makes more
sense when a role for genetic inheritance in conceded. Scholars have
occasionally puzzled over the fact that family arrangements and styles of
operation have little if any impact on the extent to which there is a match
between parental and offspring political attitudes on a wide variety of items
(see Jennings and Niemi 1968 , 180?83). Fathers do not have more influence over
sons, and mothers do not have more influence over daughters; fathers are not
generally more influential; the distribution of power within the family is
irrelevant to parent?child correlations (i.e., neither highly autocratic,
highly permissive, nor middling arrangements affect the extent to which
attitudes are correlated); the degree to which children and parents feel close
to each other does not matter; the frequency with which the family discusses
politics does not much affect correspondence between offspring and parent views
(though, as we would have predicted since it is based on active socialization,
party identification is more sensitive to family arrangements); and the extent
to which politics is important to the parents is also irrelevant. Scholars
grounded in traditional behavioralism have difficulty accounting for these
?perplexing configurations? (Jennings and Niemi 1968 , 183), but recognizing
that the correlations between the views of parents and children derive more
from genetics than familial socialization makes it much less surprising that
the strength of these correlations is not reliant on family arrangements (for
an example of political science work that does posit a role for genetics, see
Peterson 1983).

Still, the substantive findings we present here offer a direct challenge to
common assumptions and interpretations that political attitudes and behavioral
tendencies are shaped primarily or even exclusively by environmental,
especially familial, factors. Setting aside the important special case of party
identification, we find that political attitudes are influenced much more
heavily by genetics than by parental socialization. For the overall index of
political conservatism, genetics accounts for approximately half of the
variance in ideology, while shared environment including parental influence
accounts for only 11%. And in the case of the variance in people's tendencies
to possess political opinions at all, regardless of their ideological
direction, genetics explains one-third of the variance, and shared environment
is completely inconsequential.

What are the implications of these findings for political science?
Acknowledging a role for heritability in politics affects our understanding of,
first, political issues, second, political learning, and, third, political
cleavages. Inherited attitudes seem to be demonstrably different than acquired
attitudes. Tesser (1993 ) provides evidence that attitudes higher in
heritability are manifested more quickly, are more resistant to change, and
increase the likelihood that people will be attracted to those who share those
particular attitudes. It has long been known that certain political issues seem
?hard? to people, and others seem ?easy,? presumably because some issues
trigger ?gut responses? while others do not (Carmines and Stimson 1980 , 79),
but no explanation has yet been offered for why given issues do or do not
elicit gut responses. Why do social, more than economic, issues tend to hit
people in the gut, even though both constitute ongoing and equally complex
societal concerns? In light of the new findings, one distinct possibility is
that easy ?gut? issues tend to be those that are more heritable.

To the extent that political ideologies are inherited and not learned, they
become more difficult to manipulate. Conservative parents who try to make their
children conservative by carefully controlling their children's environments
are probably overestimating the importance of those environments. Offspring of
such parents are likely to end up being conservative but less because of the
environment created by the parents than the genes passed along by the parents.
A political match between parents and children should not be taken to be the
result of a socialization process?that is, the active postnatal transmission of
views?just as political mismatches between parent and child should not be taken
as evidence against a role for genetics. Parent?child mismatches are distinctly
possible given the uncertainties of meiosis (the random selection of just 50%
of each parent's DNA) and the possibility for occasional errors in the
transcription and translation of genes (mutations). These mismatches are likely
to be the primary cause of the fact that some children rebel against the views
of their parents but most do not?a pattern that environmental factors have
never explained satisfactorily.

Finally, we go into somewhat greater detail to illustrate the manner in which
results such as ours can be of use in understanding the divisions
characterizing virtually all polities and, certainly, the United States in the
early twenty-first century. Remember, genes influence people's outlooks and
personalities, and it is these broad features that then predispose individuals
toward suites of specific attitudes. This interpretation likely explains the
otherwise puzzling consistency in ideological divisions that is present across
space and time. The package of attitudes held, for example, by conservatives in
the modern United States is remarkably similar to that held by conservatives in
other cultures and at earlier times in American history (on the durability of
the liberal?conservative spectrum in the United States, see Poole and Rosenthal
1997). Environmental determinists have no convincing explanation for the
pervasiveness of this division but genetics does.

If, as our results suggest, there is a genetic basis for the varying political
views people hold, and if, as seems probable, genetic transmission frequently
affects clusters of political attitudes, we are likely to observe broad but
distinct political phenotypes. The number of these phenotypes may vary, but for
purposes of illustration we discuss two probable orientations. One is
characterized by a relatively strong suspicion of out-groups (e.g.,
immigrants), a yearning for in-group unity and strong leadership, especially if
there is an out-group threat (?Do not question the President while we are at
war with terrorists?), a desire for clear, unbending moral and behavioral codes
(strict constructionists), a fondness for swift and severe punishment for
violations of this code (the death penalty), a fondness for systematization
(procedural due process), a willingness to tolerate inequality (opposition to
redistributive policies), and an inherently pessimistic view of human nature
(life is ?nasty, brutish, and short?).

The other phenotype is characterized by relatively tolerant attitudes toward
out-groups, a desire to take a more context-dependent rather than rule-based
approach to proper behavior (substantive due process), an inherently optimistic
view of human nature (people should be given the benefit of the doubt), a
distaste for preset punishments (mitigating circumstances), a preference for
group togetherness but not necessarily unity (?We can all get along even though
we are quite different?), suspicion of hierarchy, certainty, and strong
leadership (flip-flopping is not a character flaw), an aversion to inequality
(e.g., support for a graduated income tax), and greater general empathic
tendencies (rehabilitate, don't punish).

Common political usage would call the first phenotype conservative and the
second liberal, but we seek phrases that are less connected to political
ideologies and that indicate that these two phenotypes run to the very
orientation of people to society, leadership, knowledge, group life, and the
human condition. Thus, we label the first ?absolutist? and the second
?contextualist.? This fundamental dimension offers a credible precursor to
basic cleavages manifested in a broad range of human social activity: politics
(conservatives/liberals), religion (fundamentalists/secular humanists), law
(procedural/substantive due process), education (phonics/whole language), art
(traditional form-based realism/modern free-form impressionism), sports
(football/frisbee), medicine (traditional AMA/wholistic), morality (enduring
standards/situational ethics), and scientific inquiry (formal/empirical). In
our view, all of these vexing perennial dichotomies are related cultural
expressions of a deep-seated genetic divide in human behavioral predispositions
and capabilities. We certainly are not asserting that everyone holds one of
these two orientations. Even if the individual genes involved with absolutism
or contextualism tend to move together, this does not mean they always do. Some
individuals may carry, say, an absolutist's aversion to out-groups but a
contextualist's rejection of a universalistic behavioral code. Moreover, genes
not included in these central packages, perhaps those related to extroversion,
ambition, and intelligence, often muddy the waters.

More importantly, let us not forget that a heritable component of 50% for
political ideology and probably somewhat higher for the
absolutist-contextualist dimension still leaves plenty of opportunity for the
environment to alter attitudes and behaviors?and even orientation. An
individual with a contextualist genotype who has been repeatedly victimized by
out-group members, or who has simply spent a great deal of time listening to
persuasive absolutists, may adopt attitudes that run against type. Thus, even
if a political system started with two pure genotypes, it would soon display a
fascinating array of expressed orientations and beliefs, intensity levels, and
degrees of involvement even as the system would continue to revolve around the
central division between absolutists and contextualists.

Such an account is speculative at this point but is fully consistent with the
findings presented here, with previous research on the durability of political
ideologies, and with recent events in the United States. Accounts of the 2004
election, for example, that do not invoke this fundamental difference in
orientation have fallen flat. Issues did not determine vote choice for the many
citizens who expressed disagreement with existing economic policies and/or the
war in Iraq yet still voted for the incumbent president, George W. Bush.
Indeed, if the focus remains on issues, the resultant description of the
American public is grossly at odds with reality. Morris Fiorina's (2005 )
creative analysis of survey responses indicates that Americans can be placed in
the middle on many important issues, but if this is true, then what explains
the vitriol and intensity of feeling displayed by so many ordinary Americans in
2004?

Issues do not explain Americans' politics. Many Americans admit that they do
not follow or understand the issues (Hibbing and Theiss-Morse 2002), and to the
extent they do, they support whatever their preferred politician and party
seems to support (Page and Jones 1979 ). In the 1990s, a Democratic president
(Bill Clinton) transformed welfare to workfare; then in the 2000s, his
Republican successor (George W. Bush) greatly expanded federal involvement in
both education and the provision of prescription drugs for senior citizens. If
the enactors of these policies were reversed, the groups of citizens displaying
support for the policies also would have reversed. Similarly, if a Republican
president had committed adultery with a young intern or if a Democratic
president had dramatically worsened the deficit and taken the country to war in
a far-off land on the basis of undeniably incorrect beliefs about the
opponents' nuclear and chemical weapons capabilities, the positions of most
voters on the acceptability of these conditions would be completely reversed.
Issue positions generally reflect divisions; they do not create them.

Instead, the most accurate account of voting behavior in 2004 moves beyond
issues to the basic, partially genotypic orientations described above. This
sort of broad orientation is not far removed from what most commentators are
trying to capture by reference to a ?moral? division in the electorate, but
without tying it to specific moral issues such as gay rights. The chasm
inspiring so much hostility between citizens of the United States in the early
twenty-first century did not divide supporters and opponents of privatizing
Social Security; it did not even divide supporters and opponents of gun
control. Rather, as has typically been the case, it divided absolutists and
contextualists.

And the prospects for eliminating this divide are not promising. Since mate
choice appears to be heavily tilted toward those with similar social and
political attitudes, no genetic melting pot exists for these traits. Thus, the
evidence presented here on assortative mating should be quite sobering to those
in search of unity and togetherness. If anything, the heritability of
orientation in combination with assortative mating may exacerbate the current
divide.

But admitting that genetics influences political attitudes could actually help
to mute societal divisions. Currently, absolutists and contextualists simply do
not connect, and the result is frustration. To contextualists, absolutists
appear simplistic and selfish; to absolutists, contextualists appear naive and
indecisive. Each side talks past, and is authentically miffed by, the other.
Recognizing that our political antagonists probably have a different genetic
predisposition to people, life, human nature, and politics may serve to ease
frustrations and, eventually, to improve communications across the chasm. If
absolutists spent more time trying to think like contextualists and
contextualists trying to think like absolutists, understanding would be
increased and debates could become more constructive. As frustrating as it may
be to debate with someone who holds such different orientations, value exists
in recognizing that intransigence is not the result of willful bullheadedness
but, rather, genetically driven differences in orientation.

The exciting next step is to understand the reason such distinct orientations
have evolved and lasted. Evolutionary psychologists tend to assume that all
enduring traits are adaptive (for a dissenting view, see Gould 2000 ) since
natural selection drives out variation and makes adaptive traits ever more
common. In this organism-based interpretation, whichever orientation?absolutism
or contextualism?is evolutionarily superior should soon come to numerically
dominate the other. This is possible but unlikely. An alternative group-based
interpretation sees variation itself as adaptive (see Alford and Hibbing 2004
and Sober and Wilson 1998 ). The benefits of genetic variation are most easily
observed in the ability of differential immune systems to prevent a group of
organisms from being completely wiped out by a single pathogen, but it is easy
to imagine how sociopolitical variation could also create more viable groups.
In fact, computer simulations give support to the hypothesis that divergent
individual-level social behaviors, such as cooperation and defection, are
beneficial at the group level (Hammond 2000 ). As loathe as contextualists and
absolutists are to admit it, the presence of the other orientation may make a
society stronger.

The authors gratefully acknowledge the assistance of Professor Lindon Eaves and
colleagues, particularly for granting us access to data from the sample of
twins known as Virginia 30K. Any errors in the analysis or interpretation of
the data are, of course, solely our own responsibility.

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Footnotes

1Evidence consistent with an evolutionary theory of political behavior is found
in Brewer 2000, Hibbing and Alford 2004, and Orbell et al. 2004.

2To his credit, Zaller (1992) goes on to acknowledge a possible role for
?inherited? traits in shaping predispositions (23).

3To explain this finding, opponents would need to argue that adoption agencies
are more likely to place MZ twins in similar homes than they are to place DZ
twins in similar homes. In fact, information on twin zygosity is typically
unavailable to those making placement decisions, and even if it were available,
it seems highly unlikely that it would factor into their decisions.

4However, recent research suggests that the prenatal environment is so
important that it can cause variation even in fetuses inhabiting the uterus at
the same time. Prescott, Johnson, and McArdle (1999 ) present evidence that MZ
twins sharing the same chorion, the outermost extraembryonic membrane, are more
similar in terms of personality and cognitive abilities that MZ twins in
separate chorions.

5Conservatism is not unusual in this regard. Rushton, Littlefield, and Lumsden
(1986 , 7340) find that approximately 50% of the variance in altruism is the
result of ?direct genetic inheritance,? with family environment responsible for
0%.

6Adoption studies measure the correlation of biological parents and adopted
children where the biological parents have had no contribution to the rearing
(environment) of the child. The most recent adoption study, utilizing surveys
of Korean-American adoptees randomly assigned to families in the United States,
concludes that roughly 75% of variance in children's educational attainment is
attributable to the educational attainment of their biological parents, and
only 25% is attributable to the adoptive parents, thus dramatically confirming
the earlier findings of a substantial correlation between biological parents
and adopted children and a surprisingly paltry correlation between adoptive
parents and children (Sacerdote 2004). This parallels, with an entirely
distinct methodology, the basic finding of the twin studies (see Plomin et al.
1997, 1998 and Rhee and Waldman 2002).

7Our thanks go to Professor Lindon Eaves at Virginia Commonwealth University
for making the VA30K data available to us. The data collection methods for both
studies are summarized in Lake et al. 2000 as follows: ?The Australian sample
was ascertained through two cohorts of twins. The first cohort was recruited in
1980?1982 from a sampling frame which comprised 5967 twin pairs aged 18 years
or older (born 1893 to 1964) then enrolled on the Australian NHMRC Twin
Registry (ATR). Responses were obtained from 3808 complete pairs?and these were
followed up with a second mailed questionnaire in 1988?1990 with responses from
2708 complete pairs?. The second cohort of twins, born 1964?1971, was recruited
from the ATR in 1989 and was mailed similar questionnaires in 1989?1991, with
responses from 3,769 individuals of 4269 eligible pairs?. In total there were
21,222 respondents in the Australian sample, of whom 20,945 had valid scores
for EPQ Neuroticism. The United States twins were ascertained from a
population-based birth registry for the Commonwealth of Virginia and from a
volunteer sample through the American Association of Retired Persons (AARP),
described in detail by Truett et al. (1994 ). Their first-degree relatives and
spouses were recruited in a similar fashion to the Australian sample, and in
total there were 24,905 respondents (of 29,080) with valid scores for
Neuroticism and for whom the zygosity of the proband twins could be determined.
The response rates were 70% for twins and 45% for relatives? (224?25). The
original U.S. twin data collection was funded in part by NIH grants GM30250 and
AG04954, by ADAMHA grants AA06781, AA07728, AA07535, and MH40828, and by a gift
from R. J. R. Nabisco.

8The same sort of control for parental agreement that was applied to the W?P
inventory was applied to the party affiliation analysis. Because this is only a
single item, the results are much less reliable than those averaged across the
28 items. However, despite the fact that assortative mating clearly takes place
with regard to party ID (only 24 of the 543 parent pairs had opposite party
affiliations), the general pattern of party ID being due more to shared
environment than to heredity holds up. Using a very broad definition of
disagreement (i.e., anything short of exact agreement on a five-point scale),
the shared environment estimate weakens modestly but remains high, at almost
twice the heritability estimate in the subset of twin pairs with parents in
some degree of disagreement on party affiliation.

9In this case, the different results with regard to socialism could reflect
different meanings of the phrase in the two countries. In Australia, the term
socialism is closer to a party identification label, whereas in the United
States it has more loaded ideological connotations. Likewise, the addition of
the qualifier ?nonwhite? to immigration raises questions of what the key
stimulus is.

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