The mechanism of emergenesis.

Since each individual produced by the sexual process contains a unique set of genes, very exceptional combinations of genes are unlikely to appear twice even within the same family. E. O. Wilson (1978)The intraclass correlations of monozygotic twins who were separated in infancy and reared apart (MZA twins) provide estimates of trait heritability, and the Minnesota Study of Twins Reared Apart [MISTRA: Bouchard et al. (1990), The sources of human psychological differences: the Minnesota study of twins reared apart, Science 250, 223-228] has demonstrated that MZA pairs are as similar in most respects as MZ pairs reared together. Some polygenic traits--e.g. stature, IQ, harm avoidance, negative emotionality, interest in sports--are polygenic-additive, so pairs of relatives resemble one another on the given trait in proportion to their genetic similarity. But the existence and the intensity of other important psychological traits seem to be emergent properties of gene configurations (or configurations of independent and partially genetic traits) that interact multiplicatively rather than additively. Monozygotic (MZ) twins may be strongly correlated on such emergenic traits, while the similarity of dizygotic (DZ) twins, sibs or parent-offspring pairs may be much less than half that of MZ pairs. Some emergenic traits, although strongly genetic, do not appear to run in families. MISTRA has provided at least two examples of traits for which MZA twins are strongly correlated, and DZA pairs correlate near zero, while DZ pairs reared together (DZTs) are about half as similar as MZTs. These findings suggest that even more traits may be emergenic than those already identified. Studies of adoptees reared together (who are perhaps more common than twins reared apart) may help to identify traits that are emergenic, but that also are influenced by a common rearing environment.

Parental licensure.

Most of the 1,400,000 men currently locked up in American prisons would have become tax-paying neighbors had they been switched in the hospital nursery and sent home with a mature, self-supporting, married couple. The parent with whom they did go home would in most instances not have been fit to adopt someone else's baby. It is argued that perhaps the only effective way to reduce crime and the other pathologies of the growing American underclass--apart from building still more prisons--would be to require from persons wishing to birth and rear a child of their own those same minimal criteria usually expected in adoptive parents. For evolutionary reasons, human beings are reluctant to interfere with the procreational rights of any person, no matter how immature, incompetent, or unsocialized he or she might be. In consequence, human beings tend not to think about the right of the child to a reasonable opportunity for life, liberty, and the pursuit of happiness.

The causes and costs of crime and a controversial cure.

In spite of recent modest decreases, the epidemic of crime that began in the United States in the early 1960s has left us with a rate of violent crime that is still some 300% higher than it was 40 years ago. The usual suspects--poverty, the easy availability of street drugs and handguns, violent television programs--cannot account for this ominous trend. The fact that African Americans are responsible for nearly half of this violence, although they constitute only about one-eighth of the U.S. population, is the principal reason why the great improvement in race relations made over the past half-century has reached an asymptote. White fears, and Black resentment of these fears, are a grave threat to further progress. It is argued here that the main reason for this epidemic of crime and violence is the rapid recent increase in the proportion of the young people aged 15 to 24 who have grown up unsocialized. It is argued further that most of these feral youngsters are sociopaths, defined as genetically normal children whose failure of socialization was due to their being domiciled with an immature, overburdened, unsocialized, or otherwise incompetent parent or parents.

A behavioral genetic analysis of the relationship between the socialization scale and self-reported delinquency.

This investigation examined the genetic (A), and shared (C) and nonshared (E) environmental variance contributions to the relationship of self-reported delinquency (as measured by the "Delinquent Behavior Inventory" [DBI; Gibson, 1967]) to the Socialization (So) scale of the California Psychological Inventory using univariate and bivariate structural equation models. The scales were administered to 222 male (145 monozygotic; 77 dizygotic) and 159 female (107 monozygotic; 52 dizygotic) 16- to 18-year-old same-sex twin pairs. Principal components analysis with varimax rotation revealed three interpretable So factors representing family/home environment, self-concept, and behavioral control. Univariate modeling suggested sex differences in etiological influences associated with individual differences in most scales. The bivariate ACE model fit the data, suggesting that the covariance between the So scale and self-reported delinquency owes in part to shared etiological factors.

Individual differences in electrodermal responsivity to predictable aversive stimuli and substance dependence.

To determine if the inability to take advantage of the predictability of an aversive stimulus to diminish its psychological impact reflects a deficit in inhibitory control related to the development of substance dependence, we recorded skin conductance responses (SCRs), heart rate (HR), and anticipatory electrodermal nonspecific fluctuations (NSFs) from 175 16-18-year-old boys when a white noise blast was either unpredictable or temporally predictable. Compared with boys who had moderately reduced or augmented SCRs to predictable blasts (moderate and poor modulators, respectively), boys whose SCRs were greatly reduced (good modulators) had fewer symptoms of alcohol and nicotine dependence and more anticipatory NSFs. HR appeared to index an active coping response for good and moderate modulators. The autonomic response pattern evident for good modulators may index an inhibitory control mechanism protecting them from developing substance dependence.

Incompetent parenting: its causes and cures.

The author argues that the current sharp increase in the proportion of unsocialized youth is primarily due to overburdened, incompetent, or sociopathic parenting. Because socialization, like language-learning, occurs in early childhood, the only solution to this problem is to provide alternative rearing environments for high-risk children. Parental training, adoption, professionalized foster care, group homes, and boarding schools are components of the necessary infrastructure. The best long-term solution, parental licensure, might become politically feasible once voters come to fully understand the costs to the children, and to the commonwealth, of the tradition that places procreative rights at the head of the list of human rights.

Personality and divorce: a genetic analysis.

M. McGue and D.T. Lykken (1992) found that divorce risk was, to a substantial degree, genetically mediated; prior research has identified numerous social and psychological factors that affect divorce risk (G.C. Kitson, K.B. Barbi, & M.J. Roach, 1985). The present study attempted to link these domains by examining the extent to which genetic influences on one such psychological factor, personality, explain divorce risk heritability. A sample of adult twins from the Minnesota Twin Registry completed a marital history questionnaire and the Multidimensional Personality Questionnaire (A. Tellegen, 1982). Positive Emotionality and Negative Emotionality factors were positively related to divorce risk, whereas Constraint was negatively related. In women and men, respectively, 30% and 42% of the heritability of divorce risk consisted of genetic factors affecting personality and divorce risk correlated largely as a result of these common genetic influences.

A genetic analysis of relative weight among 4,020 twin pairs, with an emphasis on sex effects.

This study replicated previous findings showing a high heritability of obesity, as measured by body mass index (kg/m2), using a measure of relative weight that does not assume a constant regression of height on weight across different populations, and evaluated whether there are sex-limited genetic effects. Subjects were 4,020 adult twin pairs. Alternative causal structural equation models were fitted to variance-covariance matrices. The ADE model (additive genetic effects, dominant/nonadditive genetic effects, and unique environment) fit best. Allowing for sex-specific effects (common sex-limitation model) significantly improved the fit, X2(6) = 230.5, p < .001. The heritability of that portion of weight unrelated to height was large: .61 for men and .73 for women.

Heritability of interests: a twin study.

The authors administered inventories of vocational and recreational interests and talents to 924 pairs of twins who had been reared together and to 92 pairs separated in infancy and reared apart. Factor analysis of all 291 items yielded 39 identifiable factors and 11 superfactors. The data indicated that about 50% of interests variance (about two thirds of the stable variance) was associated with genetic variation. The authors show that heritability can be conservatively estimated from the within-pair correlations of adult monozygotic twins reared together. Evidence for nonadditive genetic effects on interests may explain why heritability estimates based on family studies are so much lower. The authors propose a model in which precursor traits of aptitude and personality, in part genetically determined, guide the development of interests through the mechanisms of gene-environment correlation and interaction.

Is human mating adventitious or the result of lawful choice? A twin study of mate selection.

Pairs of middle-aged twins and their spouses provided data on 74 mainly psychological variables. Neither spousal similarity nor idiosyncratic criteria could account for specific mate selection in these 738 couples. Of the twins (and their spouses), 547 independently rated their initial attraction to their twin's mate (or to their spouse's twin): Findings suggest that characteristics both of the chooser and the chosen constrain mate selection only weakly. This article proposes that it is romantic infatuation that commonly determines the final choice from a broad field of potential eligibles and that this phenomenon is inherently random, in the same sense as is imprinting in precocial birds.

Age and the self-perception of ability: a twin study analysis.

Two thousand nine hundred seventy-four adults, including 678 monozygotic and 547 dizygotic twin pairs, aged 27-86 years, self-rated ability on 6 factors: Interpersonal Competence, Workplace Skills, Trade Skills, Intellectual and Cultural, Domestic Skills, and Athletic Competition. Age accounted for no more than 2% of the variance on any factor, and, although there were significant gender effects, no significant Age X Gender interactions were observed. Twin similarity did not vary significantly with age, and biometrical variance component estimates were statistically homogeneous across age with talent factor variance being apportioned approximately equally to genetic and nonshared environmental factors. Consistent failure to find age effects as well as consistent observation of significant heritability support the conclusion that self-concept crystallizes early in adulthood and reflects genetically influenced psychological characteristics.

Emergenesis. Genetic traits that may not run in families.

Traits that are influenced by a configuration--rather than by a simple sum--of polymorphic genes may not be seen to be genetic unless one studies monozygotic twins (who share all their genes and thus all gene configurations) because such "emergenic" traits will tend not to run in families. Personal idiosyncrasies that have been found to be surprisingly concordant among MZ twins separated in infancy and reared apart may be emergenic traits. More speculatively, important human traits like leadership, genius in its many manifestations, being an effective therapist or parent, as well as certain psychopathological syndromes may also be emergenic. These ideas reemphasize the importance of the role played in human affairs by genetic variation.

Why (some) Americans believe in the lie detector while others believe in the guilty knowledge test.

The accuracy of polygraphic lie detection in real life applications is very little better than chance. Yet, at least in the United States, many agencies and the polygraphers themselves have great faith in the technique. The reasons why polygraph examiners, and their clients, genuinely believe in the myth of the polygraph are explained and illustrated. A more plausible method of polygraphic interrogation, the Guilty Knowledge Test (GKT), is described and it is shown how the GKT, but not the lie test, might have resolved doubts about the case of Demjanjuk, the alleged "Ivan the Terrible."

Heterogeneity in the inheritance of alcoholism. A study of male and female twins.

Genetic influence on risk for alcoholism was examined in a US treatment sample of 50 monozygotic (MZ) and 64 dizygotic (DZ) male and 31 MZ and 24 DZ female same-sex twin pairs. For the DSM-III composite diagnosis of Alcohol Abuse and/or Dependence, statistically significant MZ/DZ differences in concordance were found with male, but not female, twins. For specific diagnoses, MZ/DZ differences were found in male subjects for both Alcohol Abuse and Alcohol Dependence, while MZ/DZ differences in female subjects were found only for Alcohol Dependence. The male MZ/DZ concordance difference for composite diagnosis but not for Alcohol Dependence could be accounted for statistically by differences in age of onset between MZ and DZ probands. As with alcohol, differences in MZ/DZ concordance were found for DSM-III composite diagnoses of Other Substance Abuse and/or Dependence with male, but not female, twins. Using Epidemiological Catchment Area data to estimate the population base rates of both alcohol and other substance use disorders allowed for heritability analyses that showed genetic factors to have only a modest influence on overall risk in both sexes (heritability estimates of approximately 0.35 for male subjects and 0.24 for female subjects). However, evidence for heterogeneity in the pattern of inheritance was also found, suggesting forms of alcoholism that may be moderately to highly heritable.

The Tridimensional Personality Questionnaire: Structural Validity and Comparison with the Multidimensional Personality Questionnaire.

Cloninger's Tridimensional Personality Questionnaire (TPQ) is a self-report inventory designed to assess Novelty Seeking, Harm Avoidance, and Reward Dependence, the three primary dimensions of his Biosocial Learning Model of normal and abnormal personality. We examined the structural validity of the TPQ and the relations among the TPQ lower- and higher-order scales to those of the Multidimensional Personality Questionnaire (MPQ; Tellegen, 1982) in a sample of 1,236 adults. The factor structure of the TPQ was congruent with Cloninger's predicted three-factor genotypic structure with one notable exception: the component scales of the Reward Dependence dimension share essentially no variance, and thus load on different factors. Both bivariate and multivariate analyses indicate that the TPQ and the MPQ share considerable variance, but that each inventory contains variance unpredicted by the other. In addition, the TPQ Harm Avoidance dimension appears to tap primarily a Negative Emotionality or neuroticism factor, rather than a disposition toward behavioral inhibition. These results support a number of Cloninger's predictions concerning the structural and external validity of the TPQ, but also suggest that the TPQ may fail to adequately operationalize several components of his model.

Sources of human psychological differences: the Minnesota Study of Twins Reared Apart.

Since 1979, a continuing study of monozygotic and dizygotic twins, separated in infancy and reared apart, has subjected more than 100 sets of reared-apart twins or triplets to a week of intensive psychological and physiological assessment. Like the prior, smaller studies of monozygotic twins reared apart, about 70% of the variance in IQ was found to be associated with genetic variation. On multiple measures of personality and temperament, occupational and leisure-time interests, and social attitudes, monozygotic twins reared apart are about as similar as are monozygotic twins reared together. These findings extend and support those from numerous other twin, family, and adoption studies. It is a plausible hypothesis that genetic differences affect psychological differences largely indirectly, by influencing the effective environment of the developing child. This evidence for the strong heritability of most psychological traits, sensibly construed, does not detract from the value or importance of parenting, education, and other propaedeutic interventions.