Congruent and incongruent semantic context influence vowel recognition.

The influence of sentence context on the recognition of naturally spoken vowels degraded by reverberation and Gaussian noise was investigated. Target words were paired to have similar consonant sounds but different vowels (e.g., map/mop) and were embedded early in sentences which provided three types of semantic context. Fifty-eight normal-hearing, young adults were presented with sentences in which acoustic and semantic cues agreed either weakly (neutral) or strongly (congruent) or the cues strongly disagreed (incongruent). One vowel pair (/epsilon/-/ae/) was selected to be easier to recognize than the other (/a/-/ae/). Changes induced in the spectra of the vowels by degradation showed that the impact of reverberation combined with noise was quite different from either condition alone. The recognition performance of participants (n=26) for isolated word stimuli matched the predictions of the frequency analysis. In sentences the recognition of the vowel was strongly influenced by the subsequent context; performance was best with congruent context and worst with incongruent context. The deleterious impact of incongruent context was larger than the helpful impact of congruent context. Incongruent context effects were greatest in noise but were also found in quiet and in reverberation.

Natural selection and quantitative genetics of life-history traits in Western women: a twin study.

Whether contemporary human populations are still evolving as a result of natural selection has been hotly debated. For natural selection to cause evolutionary change in a trait, variation in the trait must be correlated with fitness and be genetically heritable and there must be no genetic constraints to evolution. These conditions have rarely been tested in human populations. In this study, data from a large twin cohort were used to assess whether selection will cause a change among women in a contemporary Western population for three life-history traits: age at menarche, age at first reproduction, and age at menopause. We control for temporal variation in fecundity (the "baby boom" phenomenon) and differences between women in educational background and religious affiliation. University-educated women have 35% lower fitness than those with less than seven years education, and Roman Catholic women have about 20% higher fitness than those of other religions. Although these differences were significant, education and religion only accounted for 2% and 1% of variance in fitness, respectively. Using structural equation modeling, we reveal significant genetic influences for all three life-history traits, with heritability estimates of 0.50, 0.23, and 0.45, respectively. However, strong genetic covariation with reproductive fitness could only be demonstrated for age at first reproduction, with much weaker covariation for age at menopause and no significant covariation for age at menarche. Selection may, therefore, lead to the evolution of earlier age at first reproduction in this population. We also estimate substantial heritable variation in fitness itself, with approximately 39% of the variance attributable to additive genetic effects, the remainder consisting of unique environmental effects and small effects from education and religion. We discuss mechanisms that could be maintaining such a high heritability for fitness. Most likely is that selection is now acting on different traits from which it did in pre-industrial human populations.

Genetic covariation of neuroticism with monoamine oxidase activity and smoking.

Variation in the personality trait of neuroticism is known to be affected by genetic influences, but despite a number of association studies, the genes involved have not yet been characterized. In a recent study of platelet monoamine oxidase in 1,551 twin subjects, we found a significant association between monoamine oxidase activity and scores on the Eysenck Personality Questionnaire neuroticism scale. Further analyses presented here indicate that both neuroticism and monoamine oxidase activity are associated with variation in smoking habits, and that adjusting for the effect of smoking strengthens the association between MAO and neuroticism. Analysis of the genetic and environmental sources of covariation between neuroticism, smoking, and monoamine oxidase activity show that approximately 8% of the genetic variance in neuroticism is due to the same additive genetic effects that contribute to variation in monoamine oxidase activity, suggesting that variation in neuroticism is associated in part with aspects of serotonin metabolism.

Do individual differences in sociosexuality represent genetic or environmentally contingent strategies? Evidence from the Australian twin registry.

Although men are substantially more interested than women in casual sex, there is ample variation in this trait (sociosexuality) within both sexes. One theory hypothesizes that within-sex sociosexual variation results from genetic variation maintained by frequency-dependent selection. If so, sociosexuality should be substantially heritable. A competing theory is that children acquire their mating strategy after observing their parents' relationship. By this theory, sociosexuality should reveal a strong shared environmental component. The authors studied genetic and environmental influences on sociosexuality using a large, representative volunteer twin sample. Parental marital instability was modestly associated with sociosexuality, but this could have been due to either genetic or environmental factors. Consistent with genetic theory, familial resemblance appeared primarily due to additive genetic rather than shared environmental factors.

Induction of congenital malformations in the offspring of male mice treated with X-rays at pre-meiotic and post-meiotic stages.

The induction of congenital malformations among the offspring of male mice treated with X-rays at pre-meiotic and post-meiotic stages has been studied in two experiments. Firstly, animals were exposed to varying doses (108-504 cGy) of X-rays and mated at various time intervals (1-7, 8-14, 15-21 and 64-80 days post-irradiation), so as to sample spermatozoa, spermatids and spermatogonial stem cells. In the second experiment, only treated spermatogonial stem cells were sampled. One group of males was given a single 500-cGy dose, a second group a fractionated dose (500 + 500 cGy, 24 h apart) and a third group was left unexposed. In the first experiment, induced post-implantation dominant lethality increased with dose, and was highest in week 3, in line with the known greater radiosensitivity of the early spermatid stage. Preimplantation loss also increased with dose and was highest in week 3. There was no clear induction of either pre-implantation or post-implantation loss at spermatogonial stem cell stages. There was a clear induction of congenital malformations at post-meiotic stages, the overall incidence being 2.0 +/- 0.32% in the irradiated series and 0.24 +/- 0.17% among the controls. The induction was statistically significant at each dose. At the two highest doses the early spermatids (15-21 days) appeared more sensitive than spermatozoa, and at this stage the incidence of malformations increased with dose. The data from Expt. 1 on the induction of malformations by irradiation of spermatogonial stages were equivocal. In contrast, Expt. 2 showed a statistically significant induction of malformations at both dose levels (2.2 +/- 0.46% after 500 cGy and 3.1 +/- 0.57% after 500 + 500 cGy). The relative sensitivities of male stem cells, post-meiotic stages and mature oocytes to the induction of congenital malformations were reasonably similar to their sensitivities for specific-locus mutations, except that the expected enhancing effect of the fractionation regime used was not seen. Dwarfism and exencephaly were the two most commonly observed malformations in all series.

Discrimination between the effects of X-ray irradiation of the mouse oocyte and uterus on the induction of dominant lethals and congenital anomalies.

In order to test whether irradiation of the postimplantation maternal environment had any effect on the apparent induction of dominant lethals or congenital anomalies by radiation, preimplantation embryos were surgically transferred between females which had been irradiated before conception or left untreated. A high proportion of preimplantation embryos, collected from females that had been irradiated 15-21 days prior to conception with 3.6 Gy X-rays, were either arrested or developmentally retarded compared with those collected from untreated females. The transfer experiments indicate that irradiation of the uterus has no significant effect on the frequency of subsequent postimplantation mortality or on mean fetal weight. However, it remains unclear whether irradiation of the uterus contributes to the induction of congenital anomalies.

Discrimination between the effects of X-ray irradiation of the mouse oocyte and uterus on the induction of dominant lethals and congenital anomalies. II. Localised irradiation experiments.

In order to evaluate whether irradiation of the postimplantation maternal environment contributed to the induction of postimplantation mortality or congenital anomalies, mouse ovaries were surgically exteriorised and selectively irradiated or shielded in a specially constructed apparatus. The results show that exposure of the mouse abdomen and uterus to 3.70 Gy X-rays, 15-21 days prior to conception, has no significant effect on the incidence of either postimplantation mortality or congenital anomalies. Exposure of the ovaries to 3.27 Gy X-rays during the same period, however, increased the frequency of both postimplantation mortality and congenital anomalies.

Self-transcendence as a measure of spirituality in a sample of older Australian twins.

Measures of self-transcendence, physical health and psychological well-being were included in a self-report Health and Lifestyle questionnaire administered to Australian twins aged over 50 between 1993 and 1995. Self-transcendence appears to be higher among older Australian women than men, and was significantly associated with religious affiliation, marital status (in women) and age (in men). No strong correlations were observed between self-transcendence and any measure of psychological or physical health. Additive genetic effects were found to be important in influencing self-transcendence, with heritability estimates of 0.37 and 0.41 for men and women respectively, whilst shared environment effects were not found to be significant. Multivariate modelling of self-transcendence scores and self-reported church attendance behavior indicated substantially different etiologies for these variables, with implications for methods of investigation of religiosity and spirituality.

How accurate is the family history method for assessing siblings' sexual orientation?

Previous studies investigating the familial nature of sexual orientation have often relied on the reports of siblings. They have generally obtained extremely high accuracy rates for proband rating of the sexual orientation of siblings. However, participants in these studies have probably been unusually open about their sexual orientation, and thus it is uncertain if more representative participants would have as accurate knowledge about their families. An unselected sample of twins from the Australian Twin Registry rated their own, their cotwins', and their siblings' sexual orientations. We examined accuracy of heterosexual and homosexual probands' assessments of their twins' sexual orientations, as well as cotwins' agreement about other siblings' orientations. Concordance between twins' ratings of their cotwins' orientations with the cotwins' self-rated orientations was considerably lower than that found in previous studies, as was the level of agreement between members of a twin pair in the assessment of other siblings' sexual orientations. Marital history as a proxy variable for determining the sexual orientation of older subjects did not support its use with women, though its use for older men received some weak support.

Fatigue as related to anxiety and depression in a community-based sample of twins aged over 50.

Measures of fatigue, anxiety and depression were administered in self-report questionnaire format to a community-based sample of 2703 Australian twins aged over 50. Factor analysis indicated that a two-factor solution was appropriate and demonstrated a clear separation between fatigue-related items and questionnaire items relating to anxiety and depression. Highly congruent factor structures were derived for male and female subjects.

Genetic and social determinants of initiation and age at onset of smoking in Australian twins.

Retrospective data on age at onset of smoking, reported by 3810 adult Australian twin pairs, were analyzed to determine the role of genetic and environmental factors in the onset of smoking. Results of nonmetric multidimensional scaling supported a two-process model in which different etiologic factors determined which individuals were at risk of becoming smokers and the age at onset of smoking in those who were at risk. Parametric model-fitting confirmed this difference. For female twins and younger male twins (aged 30 years or less), the onset of smoking was strongly influenced by genetic factors, with shared and nonshared environmental effects having a more modest impact. For older male twins, shared environmental influences on onset of smoking were very important, and the influence of genetic predisposition was slight. The age at which smoking onset occurred, however, was influenced by both genetic and nonshared environmental effects, but not by shared environmental effects, in both sexes and both cohorts.

Effects of lifestyle, personality, symptoms of anxiety and depression, and genetic predisposition on subjective sleep disturbance and sleep pattern.

The effects on sleep pattern ('short-sleep' versus 'long-sleep') and subjective sleep disturbance of genotype, personality, symptoms of anxiety and depression, and lifestyle, were examined using survey data on a clinically unselected sample of adult Australian twin pairs, aged 17-88 years. When the effects of genotype, personality and symptoms were ignored, lifestyle variables appeared to account for roughly 4% of the variance in sleep disturbance, and 9% of the variance in sleep pattern. Significant genetic effects on sleep disturbance and sleep pattern were found, which were only partly explained by the effects of personality and symptoms of anxiety and depression. Much of the association between sleep disturbance and lifestyle appeared to be explained by separate effects of personality and symptoms of anxiety and depression on sleep and lifestyle ('genotype-risk-factor correlation'). There was little evidence for genetically determined differences in sensitivity to the lifestyle variables ('genotype x risk-factor interaction').

Some implications of chaos theory for the genetic analysis of human development and variation.

Non-linear epigenetic processes are a potential underlying source of phenotypic differences in development. Simulation studies of twin pairs using simple non-linear development models characterised by chaotic or near-chaotic behavior are presented. The effect of chaotic processes on correlations is to lower them from their initial values, but high initial correlations are affected much less by chaotic and near-chaotic processes than intermediate correlations. Therefore, we would predict that traits affected by chaotic processes would have high MZ and low DZ twin correlations and this is reminiscent of certain traits such as EEG spectra. However the much more frequent observation of MZ correlations close to twice their DZ counterparts would suggest that the role of chaos in development is quite limited.

Somatic distress as a distinct psychological dimension.

BACKGROUND: Somatoform disorders such as neurasthenia and chronic fatigue are characterized by a combination of prolonged fatigue and disabling neuropsychological and neuromuscular symptoms. However, the debate concerning the theoretical underpinnings of somatic disorders resembles the perennial dispute over the taxonomy of anxiety and depression. The objective of this study is to analyse the dimensional structure of items measuring anxiety, depression, phobic anxiety, somatic distress, and insomnia. It is anticipated that somatic distress should emerge as empirically distinct from measures of anxiety and depression, thereby lending support to proponents of the construct as independent of both anxiety and depression symptomatology. METHODS: A 33-item self-report symptom inventory derived from the SCL-90 and DSSI/sAD scales was used to measure recently experienced psychiatric distress in the form of depression, anxiety, phobic anxiety, somatic distress, and insomnia. SCL and DSSI/sAD items were measured on a four-point distress scale from 1 'not-at-all' to 4 'unbearably'. The inventory was administered to a community-based sample of 3468 Australian twins between the ages of 18 and 28. RESULTS: Factor analysis using Polychoric correlations and a Promax rotation criterion produced four factors: depression, phobic anxiety, somatic distress, and sleep disturbance. CONCLUSION: Results from the current factor analysis, together with the documented prevalence of somatic disorders, including evidence regarding the genetic and biological independence of somatic symptomatology, lend support to the argument that somatic symptoms, although correlated, are independent of anxiety and depression.

Twin study of adolescent genetic susceptibility to mosquito bites using ordinal and comparative rating data.

Ordinal and comparative rating measures of mosquito attraction and mosquito bite frequency and symptoms were administered in a self-report questionnaire format to a sample of 197 monozygotic and 326 dizygotic Australian adolescent twin pairs at age 12 between 1992 and 1999, in order to investigate the environmental and possibly genetic determinants of variation between individuals. Repeat measures were obtained from the twin pairs at age 14. Ordinal variable measures, although providing some support for genetic effects on mosquito susceptibility, were affected by low repeatability. However, analysis of a comparative rating variable "compared with your twin, who is bitten by mosquitoes more often?" indicated a strong genetic influence on frequency of being bitten by mosquitoes, with no significant differences observed between males and females. Comparative rating questionnaire items are a potentially valuable tool for complementing and improving the results obtained from more conventional absolute measures.

Shared and unique environmental factors determine the ecology of methanogens in humans and rats.

OBJECTIVE: This study ascertains the relative contributions of genetics and environment in determining methane emission in humans and rats. There is considerable interest in the factors determining the microbial species that inhabit the colon. Methanogens. which are archaebacteria, are an easily detected colonic luminal bacteria because they respire methane. They are present in some but not all human colons and lower animal hindguts. Opinion varies on the nature of the factors influencing this ecology with some studies proposing the existence of host genetic influences. METHODS: Methane emission was measured in human twin pairs by gas chromatography, and structural equation modeling was used to determine the proportion of genetic and environmental determinants. The importance of the timing of environmental effects and rat strain on the trait of methane emission were ascertained by experiments with cohabiting methanogenic and nonmethanogenic rats. RESULTS: Analysis of breath samples from 274 adolescent twin pairs and their families indicated that the major influences on the trait of methane emission are the result of shared (53%, 95% confidence interval 39-61) and unique environmental (47%, 95% confidence interval 38-56) effects. No significant autosomal genetic effects were detected, but as observed in other studies, men (37%) were less likely to excrete methane in their breath than women (63%). Investigation of methane emission in rats indicated that environmental effects in this animal are most potent during the weaning period, with stable gut microbial ecology thereafter for some but not all rat strains. CONCLUSIONS: These results are consistent with shared and unique environmental factors being the main determinants of the ecology of this colonic microbe.

Measurement models for sexual orientation in a community twin sample.

Multivariate structural equation modeling techniques have been applied to examine the causes of individual differences in responses to several items concerning sexual orientation. To minimize potential ascertainment and response biases, the study sample involved a large (N = 4901) community-based cohort of Australian twins aged 18-52 who answered an anonymous questionnaire on sexual behavior and attitudes. The statistical power of the analysis was increased by the availability of multiple measures of sexual orientation (behaviors, attitudes and feelings), providing stronger evidence for the existence of additive genetic influences on this phenotype than in a previous analysis (Bailey et al., 2000). Estimates of the heritability of homosexuality in this sample ranged between 50 and 60% in females but were significantly lower (heritability of approximately 30%) in males.

The subtlety of sex-atypicality.

Memories of sex-atypical behavior and interests in childhood usually differ between homosexual and heterosexual people. However, variation within these broad groups has not previously been explored in detail, especially among women. We utilized data from a postal survey of a nationwide sample of Australian adult twins (n = 4,901, age range: 19-52 years). Among men, 15.2% reported homosexual behavior (ever), 11.5% said they had been sexually attracted to the same sex, and 6.4% said they were not heterosexual; the corresponding figures for women were 7.9, 10.6, and 3.5%. A continuous measure of childhood gender nonconformity (CGN) was sensitive to slight variations in homosexual attraction and behavior. In particular, among both men and women who identified as heterosexual, there were significant differences between "complete" heterosexuals and those who admitted to only one or a few same-sex behaviors but no homosexual attraction. Among men, CGN scores distinguished between heterosexuals who admitted to same-sex behavior only and those who admitted to some homosexual attraction. The sexual subgroups also differed on a measure of gender atypicality in adulthood. Implications for developmental theories of sexuality are discussed.

Frequency of church attendance in Australia and the United States: models of family resemblance.

Data on frequency of church attendance have been obtained from separate cohorts of twins and their families from the USA and Australia (29,063 and 20,714 individuals from 5670 and 5615 families, respectively). The United States sample displayed considerably higher frequency of attendance at church services. Sources of family resemblance for this trait also differed between the Australian and US data, but both indicated significant additive genetic and shared environment effects on church attendance, with minor contributions from twin environment, assortative mating and parent-offspring environmental transmission. Principal differences between the populations were in greater maternal environmental effects in the US sample, as opposed to paternal effects in the Australian sample, and smaller shared environment effects observed for both women and men in the US cohort.

Phenotypic and genetic analyses of a short measure of psychosis-proneness in a large-scale Australian twin study.

Previous genetic analyses of psychosis proneness have been limited by their small sample size. For the purposes of large-scale screening, a 12-item questionnaire was developed through a two-stage process of reduction from the full Chapman and Chapman scales. 3685 individuals (including 1438 complete twin pairs) aged 18-25 years and enrolled in the volunteer Australian Twin Registry returned a mail questionnaire which included this psychosis proneness scale and the Eysenck Personality Questionnaire. Despite the brevity of the questionnaire, item and factor analysis identified four unambiguous and essentially uncorrelated scales. There were (1) Perceptual Aberration--Magical Ideation; (2) Hypomania--Impulsivity/Nonconformity; (3) Social Anhedonia and (4) Physical Anhedonia. Model-fitting analyses showed additive genetic and specific environmental factors were sufficient for three of the four scales, with the Social Anhedonia scale requiring also a parameter for genetic dominance. There was no evidence for the previously hypothesised sex differences in the genetic determination of psychosis-proneness. The potential value of multivariate genetic analysis to examine the relationship between these four scales and dimensions of personality is discussed. The growing body of longitudinal evidence on psychosis-proneness suggests the value of incorporating this brief measure into developmental twin studies.