Hereditary factors in normal personality traits (as measured by inventories)

Individual differences in multiple dimensions of aggression: a univariate and multivariate genetic analysis

Previous behaviour genetic studies of aggression have yielded inconsistent results: reported heritabilities for different types of aggressive behaviour ranging from 0 to 0.98. In the present study, 247 adult twin pairs (183 MZ pairs; 64 same-sex DZ pairs) were administered seven self-report questionnaires which yielded 18 measures of aggression. Univariate genetic analyses showed moderate to high heritabilities for 14 of these 18 measures and for a general aggression factor and three correlated aggression factors extracted from the measures. Multivariate genetic analyses showed sizeable genetic correlations between the different dimensions of aggression. Thus, individual differences in many types of aggressive behaviour are attributable to some extent to genetic factors and there is considerable overlap between the genes that operate on different types of aggressive behaviour.

Personality development and temperament

This paper identifies a number of problems that emerge in our attempts to trace a developmental linkage between early-appearing individual differences in temperament and later personality. It is suggested that the major problem is that of inadequate theory, from which it follows that there will be problems of definition and methodology. Attention is also drawn to difficulties associated with the concept of 'development'. Certain early-appearing individual difference are identified, for which there is accumulating evidence of a genetic or constitutional basis. Further, these appear to show some stability and are accorded an important role in a number of theories, especially that of Eysenck. It is suggested that his approach, despite its many limitations, is worth further exploration.

Are heritability estimates generalizable? Lack of evidence from cross-sample correlations

The majority of research indicates that estimates of heritability are not generalizable beyond the specific sample on which they have been calculated. This research has been limited, however, in its scope. The present set of investigations center upon an examination of previously reported heritability estimates for the scales of the Minnesota Multiphasic Personality Inventory (MMPI). The first investigation correlates the estimates for eight samples derived from a variety of published studies. The second investigated correlates the DZ twin pair and MZ twin pair intraclass correlations from four of the first investigation's samples. The third investigation correlates the estimates from one study in which the same sample was tested twice over a period of less than five years. It is concluded that no evidence is available for the generalizability of these estimates of MMPI scale heritability either across samples or even across time with the same sample.

Behavioral genetics and personality change

Although research on personality and behavioral genetics has focused on the continuity of traits, both fields and their interface will profit from the consideration of trait change. In this article we review personality research on age differences in heritability and propose the counterintuitive hypothesis that, when developmental changes in heritability are found, heritability tends to increase. We also focus on behavioral genetic analyses of long-term developmental change. Research to date suggests that genetic involvement in adult personality change is slight whereas personality change in childhood is governed substantially be genetic factors. Finally, we consider a new topic, genetic influence on short-term change in personality.

Genetic and environmental influences on obsessional traits and symptoms

A biometrical genetic analysis was carried out on the response of 419 pairs of twins to the 42-item version of Leyton Obsessional Inventory. Just under half the variation in both the Obsessional Trait and Symptom Scales was due to heredity. Multivariate analysis revealed a genetic effect on the development of obsessional personality and also the transmission of a general tendency predisposing to neurotic breakdown. Although the influence of heredity was outweighed by that of the environment, the latter effect showed an absence of general factors and, in particular, of any noticeable effect from the common home environment.

A twin methodology for the study of genetic and environmental control of variation in human smoking behavior

A method is presented for partitioning the variance associated with human smoking behavior into additive genetic, nonadditive genetic, prenatal environmental, postnatal familial environmental, and postnatal extrafamilial environmental components. Estimations can also be made of additive genetic and residual correlations between spouses and of the correlation between parental additive genetic effect and progeny nonadditive genetic and environmental effect. The variance estimates are free of the biases that might result from these correlations. The statistical genetic analysis is being applied to a large group of MZ and DZ twins, their spouses, and their adult children who live in southern Sweden. Blood samples from each subject will be used to identify their genetic constitution for a number of biochemical polymorphisms, some of which may be considered a priori to have possible relationships to smoking. Associations and genetic linkages between biochemical marker loci and quantitative behavioral traits will be sought. Traits of interest include a wide array of tobacco-use variables, motives for smoking, personality and cognitive variables, and other variables associated with drug use and health. Zygosity determinations based on biochemical polymorphisms have indicated MZ to DZ and DZ to MZ misclassification rates of 0% and 6.15%, respectively, when based solely on external morphology and questionnaire data. The nonpaternity ratio of the fathers with respect to their supposedly biological children is estimated to be 0.28%. Gene frequency estimates for 21 marker loci show that the sample of twins and their relatives is quite representative of the Swedish population at large. All loci were in Hardy-Weinberg-Castle equilibrium, with no evidence of assortative mating for biochemical traits. The MZ twins are significantly more concordant than the DZ twins with respect to whether they have ever had a smoking habit.

The electroencephalogram (EEG) as a research tool in human behavior genetics: psychological examinations in healthy males with various inherited EEG variants. I. Rationale of the study. Material. Methods. Heritability of test parameters

In the first section of this paper, various research designs in human behavior genetics are compared. In this context, the commonly used concept of biometric genetics is critically evaluated from the point of view of science theory. It is contrasted with the Mendelian gene concept, which, in principle, leads to a much deeper theoretical understanding by offering clues for basic mechanisms. To explore this advantage fully, a research strategy is needed that first looks for genetic variability in a physiological parameter of possible importance for human behavior and then tries to explore the influence of this parameter on the function of the human brain and on behavior. If possible, this genetic parameter should be selected in a way that inferences as to the mechanism of its influence on behavior become feasible. Such genetic variability is provided by the hereditary variants of the normal EEG discovered by earlier work (cf. Vogel, 1970). In the following section, a research program on 298 adult healthy males, most of them soldiers, with various inherited EEG variants is described. Apart from controls with inconspicuous EEGs, this material comprises probands with the following EEG variants: low-voltage (N); low-voltage borderline (NG); monotonous alpha-waves (R); occipital fast alpha-variants (BO); fronto-precentral beta-groups (BG), and diffuse beta-waves (BD). In addition to an EEG examination, the probands were examined with various test methods measuring intelligence (IST; LPS; Raven); working speed and concentration (d-2; KLT); personal attitudes (MMPI; 16PF; RKS); and sensory and motor abilities (flicker fusion; tachistoscopy; reaction time to optic, acoustic and combined stimuli; two-hand dexterity; pursuit rotor; tapping). In a supplementary twin study on 52 male adult twin pairs (26 MZ, 26 DZ), heritabilities were determined for the test scores included in the main study. For most test scores, heritabilities are relatively low; the data are compared with those from the literature. We conclude that the test methods utilized in the main study (on EEG variants) are expected to demonstrate at the most a small to moderate correlation of the EEGs with psychological phenotypes as defined by test examinations, even if a major part of the genetic variability underlying these phenotypes would be due to differences in brain physiology that could be revealed by EEG variation.

Biogenic amine-related enzymes and personality variations in normals

Altered activities of biogenic amine-related enzymes have been reported in some studies of patients with affective disorders and chronic schizophrenia. To evaluate whether any relationship between personality variations, including non-diagnosed psychopathology, and these enzymes might occur in non-psychiatric patients, 95 young adult volunteers were studied. Higher MMPI and Zuckerman sensation--seeking scale scores were found in male, but not female, volunteers with lower platelet and plasma amine oxidase activities. Males generally exhibited negative correlations, while females had positive correlations between the psychological test scores and amine oxidase activities. In contrast to the amine oxidase results, no associations were observed between plasma dopamine beta-hydroxylase activities and the personality variables.

Twins: within-pair similarity on Bayley's Infant Behavior Record

Summary scores for behaviors rated on Bayley's Infant Behavior Record were obtained by summing sequential ratings for same-sex twins participating in a longitudinal study. The first year scores were based on visits made at 3, 6, 9, and 12 months, by 55 identical and 27 fraternal pairs; the second year scores were based on visits at 18, 24, and 30 months, by 47 identical and 27 fraternal pairs. During the first year, within-pair correlations for almost all behaviors were stronger for identical than for fraternal pairs; in the second year, within-pair correlations for identical twins were similar to those of fraternal twins except for the more cognitive behaviors. Composite scores were calculated for two behavioral clusters--one composed of behaviors related to Primary Cognition, and the other composed of behaviors related to Extraversion. Within-pair correlations were higher for identical than for fraternal twins in both the first and second years, indicating stronger and more consistent genetic influences on the more cognitive behaviors.

School achievement, intelligence, and personality in twins

A sample of 47 MZ and 49 DZ pairs of Brazilian twins was investigated in relation to school achievement in six specific areas of study, as well as performance in the test of Dominoes, the Differential Aptitude Tests (DAT) and Grieger's Characterological Qur the school grades obtained in five of the six areas considered, as well as for their general average; the same being true for the results on the indicated measure of general intelligence, six of the eight DAT tests, and two of the characterological elements. There is a clear positive relationship between the grades earned by the twins and their performance in the Dominoes test. Achievement in Portuguese and foreign language correlates positively with DAT's Numerical Ability, Abstract Reasoning, and Clerical Speed and Accuracy. The results show an agreement with previous estimates of the genetic determination of these variables, which is to a certain extenet surprising if we consider the differences in sample sizes, age, and degree of schooling of the subjects, environmental differences, and the dissimilarities which exist between the homes and school systems of USA, Europe, and Brazil.

Field-dependent introvert and neuroticism: Eysenck and Witkin united

Based on derivations from the theories of Witkin and Eysenck, it was predicted that field-dependent introverts would have a higher incidence of neuroticism (above the 70th percentile, as measured by personality tests) than any other combination of the field-dependence and extraversion dimensions. The relationship was verified six times utilizing data from previously completed studies. Broad implications of the possibly genetically based results are discussed and potentially fruitful areas of investigation are noted.

The inheritance of neurotic traits: a twin study of the Middlesex Hospital Questionnaire

The Middlesex Hospital Questionnaire (M.H.Q.) is a self-rating scale designed to provide rapid quantification of common symptoms and traits relevant to the conventional clinical categories of psychoneurotic illness. The inventory comprises 48 brief questions for each of which two or three simple alternative answers are provided. By use of a standard key, the following six subtest scores are easily calculated: free-floating anxiety (FFA), phobic anxiety (PHO), somatic concomitants of anxiety (SOM), obsessional traits and symptoms (OBS), depression (DEP), and hysterical personality traits (HYS). In that the questionnaire provides an approximation to what would be expected at a clinical level from a diagnostic psychiatric interview, it has advantages over other questionnaires which incorporate essentially non-clinical constructs of personality functioning.

A TWIN STUDY OF SPATIAL ABILITY

A battery of spatial visualization land form percepthn plus some tests of arithmetic, vocabulary and social perception has been administered to 274 pairs of identical and 198 pairs of frabmal twins. To assess the importance of hereditary components in the individual differences observed, the within pair variance for fraternal paim was compared with the within pair vazianw for identical pains by the F ratio test. The results for 123 pairs of identiml twins and 91 pairs of fraternal twins on the spatial task, were classified in terms of the apparent psychological task requirements of the test. It appears that tests requiring three-dimensional manipdadion of drawings demonstrate more frequently a statistically significant hereditary component.