Iris pigmentation and behavioral inhibition

Iris colour and subjective emotional status in Chinese adolescents

BACKGROUND

Understanding the iris colour might be a useful biomarker in predicting emotional health status. We aimed to examine the relationship of iris colour with subjective emotional status in a sample of Chinese adolescents aged 13 to 14 years.

METHODS

A total of 2346 students from ten middle schools in Mojiang participated the examination. The emotional health status was measured by the adolescent self-reported PedsQL 4.0. We obtained standardized slit-lamp photographs and developed a grading system assessing iris colour (higher grade denoting darker). Logistic regression models were fitted to assess the relationship between iris colour and emotional status.

RESULTS

The trend of decreasing negative emotional status with darker iris colour was significantly. Compared with grades 1 and 2 of iris colour, the students with grades 4 and 5 had less negative emotional status (ORfear = 0.56, 95 % CI: 0.41, 0.76; ORsadness = 0.67, 95 % CI: 0.49, 0.92; ORanger = 0.71, 95 % CI: 0.52, 0.98). In addition, the trend did not change after adjusting for potential confounders, including height, waist circumstance, sleep habits and computer times in logistic regression models.

LIMITATIONS

Only negative emotional indexes were selected as evaluative materials, it is unclear whether the pattern found in the present study also exists with regard to positive emotional indexes, such as happiness.

CONCLUSION

Darker iris colour might be associated with less negative emotional status in Chinese adolescents.

Infant Predictors of Inhibited and Uninhibited Profiles

Previous research on subjects showing the two temperamental profiles called inhibited and uninhibited to unfamiliar events suggests that the two groups differ in threshold of reactivity to novelty. Hence, variation among infants in behavioral reactivity to unfamiliar events might predict later display of the two profiles. In a longitudinal study of 94 four-month-old infants, those who displayed the combination of high motor activity and frequent crying to stimulation were more fearful to unfamiliar events at nine and 14 months than infants who displayed both low motor activity and infrequent crying. This result implies that the processes that mediate early reactivity to stimulation may also influence a later preparedness to avoid or to approach unfamiliarity.

Human Commercial Models' Eye Colour Shows Negative Frequency-Dependent Selection

In this study we investigated the eye colour of human commercial models registered in the UK (400 female and 400 male) and Brazil (400 female and 400 male) to test the hypothesis that model eye colour frequency was the result of negative frequency-dependent selection. The eye colours of the models were classified as: blue, brown or intermediate. Chi-square analyses of data for countries separated by sex showed that in the United Kingdom brown eyes and intermediate colours were significantly more frequent than expected in comparison to the general United Kingdom population (P<0.001). In Brazil, the most frequent eye colour brown was significantly less frequent than expected in comparison to the general Brazilian population. These results support the hypothesis that model eye colour is the result of negative frequency-dependent selection. This could be the result of people using eye colour as a marker of genetic diversity and finding rarer eye colours more attractive because of the potential advantage more genetically diverse offspring that could result from such a choice. Eye colour may be important because in comparison to many other physical traits (e.g., hair colour) it is hard to modify, hide or disguise, and it is highly polymorphic.

Not everything is blue or brown: Quantification of ocular coloration in psychological research beyond dichotomous categorizations

The notion that phenomenologically observable differences in the human eye are correlated with behavioral tendencies (other than gaze-following) has been addressed poorly in the psychological literature. Most notably, the proposed correlations are based on an arbitrary categorization in discrete categories of the continuous variability across various traits that could be contributing to individual eye morphologies. We review the relevant literature and assume a view of human eyes as sign stimuli, identifying the relative contrast between the iridal and scleral areas as the main contributor to the strength of the signal. Based on this view, we present a new method for the precise quantification of the relative luminosity of the iris (RLI) and briefly discuss its potential applications in psychological research.

Trustworthy-looking face meets brown eyes

We tested whether eye color influences perception of trustworthiness. Facial photographs of 40 female and 40 male students were rated for perceived trustworthiness. Eye color had a significant effect, the brown-eyed faces being perceived as more trustworthy than the blue-eyed ones. Geometric morphometrics, however, revealed significant correlations between eye color and face shape. Thus, face shape likewise had a significant effect on perceived trustworthiness but only for male faces, the effect for female faces not being significant. To determine whether perception of trustworthiness was being influenced primarily by eye color or by face shape, we recolored the eyes on the same male facial photos and repeated the test procedure. Eye color now had no effect on perceived trustworthiness. We concluded that although the brown-eyed faces were perceived as more trustworthy than the blue-eyed ones, it was not brown eye color per se that caused the stronger perception of trustworthiness but rather the facial features associated with brown eyes.

The emergence of human-evolutionary medical genomics

In this review, I describe how evolutionary genomics is uniquely suited to spearhead advances in understanding human disease risk, owing to the privileged position of genes as fundamental causes of phenotypic variation, and the ability of population genetic and phylogenetic methods to robustly infer processes of natural selection, drift, and mutation from genetic variation at the levels of family, population, species, and clade. I first provide an overview of models for the origins and maintenance of genetically based disease risk in humans. I then discuss how analyses of genetic disease risk can be dovetailed with studies of positive and balancing selection, to evaluate the degree to which the 'genes that make us human' also represent the genes that mediate risk of polygenic disease. Finally, I present four basic principles for the nascent field of human evolutionary medical genomics, each of which represents a process that is nonintuitive from a proximate perspective. Joint consideration of these principles compels novel forms of interdisciplinary analyses, most notably studies that (i) analyze tradeoffs at the level of molecular genetics, and (ii) identify genetic variants that are derived in the human lineage or in specific populations, and then compare individuals with derived versus ancestral alleles.

Genomic imprinting in the development and evolution of psychotic spectrum conditions

I review and evaluate genetic and genomic evidence salient to the hypothesis that the development and evolution of psychotic spectrum conditions have been mediated in part by alterations of imprinted genes expressed in the brain. Evidence from the genetics and genomics of schizophrenia, bipolar disorder, major depression, Prader-Willi syndrome, Klinefelter syndrome, and other neurogenetic conditions support the hypothesis that the etiologies of psychotic spectrum conditions commonly involve genetic and epigenetic imbalances in the effects of imprinted genes, with a bias towards increased relative effects from imprinted genes with maternal expression or other genes favouring maternal interests. By contrast, autistic spectrum conditions, including Kanner autism, Asperger syndrome, Rett syndrome, Turner syndrome, Angelman syndrome, and Beckwith-Wiedemann syndrome, commonly engender increased relative effects from paternally expressed imprinted genes, or reduced effects from genes favouring maternal interests. Imprinted-gene effects on the etiologies of autistic and psychotic spectrum conditions parallel the diametric effects of imprinted genes in placental and foetal development, in that psychotic spectrum conditions tend to be associated with undergrowth and relatively-slow brain development, whereas some autistic spectrum conditions involve brain and body overgrowth, especially in foetal development and early childhood. An important role for imprinted genes in the etiologies of psychotic and autistic spectrum conditions is consistent with neurodevelopmental models of these disorders, and with predictions from the conflict theory of genomic imprinting.

Eye Color as an Indicator of Behavior: Revisiting Worthy and Scott

Phenotypic eye color has been suggested as an indicator of genetic predisposition toward certain behaviors both in humans and in animals. Previous research has yielded mixed results. Phototaxic and ethological behaviors were examined in 14 different strains of Drosophila melanogaster. No significant correlation between phenotypic eye coloration and behavior was found, although significant genotypical behavioral differences were noted even among subjects with similar eye colors. An analysis of cellular defects associated with eye color in D. melanogaster pointed to significant behavioral differences among cell-defect groups, indicating that the cell defect which causes eye color, rather than eye color itself, may serve as a crude indicator of behavior.

Association of behavioral inhibition with hair pigmentation in a European sample

Behavioral inhibition, a temperamental trait signalling a predisposition to childhood and adolescent anxiety disorders, is slightly more frequent in America among Caucasian children having blue irises. This paper examines a community sample of 101 German toddlers assessed for behavioral inhibition in a standardized laboratory procedure. Hair pigmentation was found to be significantly associated with behavioral inhibition in the sense that blond children exhibited higher fear scores. As in American samples, blue-eyed children had a higher fear score than did other children, but this difference was not statistically significant.

Accurate social perception at zero acquaintance: the affordances of a Gibsonian approach

We review research on accurate social perception at zero acquaintance and apply a Gibsonian ecological approach to redress several shortcomings. We argue that recent use of Brunswik's lens model to determine what physical qualities accurately communicate psychological traits has limited utility because it fails to consider the structured information provided by configural physical qualities that is central to Gibson's (1979) theory. We elaborate a developmental model of relationships between physical and psychological qualities that highlights research needed to identify configural physical qualities that may inform accurate perceptions. This model and tenets of the ecological theory yield several hypotheses regarding such qualities. Finally, we advocate the value of studying perceived affordances (opportunities for acting, interacting, or being acted upon) because this will focus attention on the neglected issue of contextual influences on social perception accuracy, and because affordances may be perceived more accurately than global personality traits.

Can Prenatal Caffeine Exposure Affect Behavioral Inhibition?

Given the widespread use of caffeine and its potential nonoptimal effects during pregnancy, it is remarkable and distressing that almost nothing is known about the long-term effects of prenatal caffeine exposure in humans. Research on nonhumans reveals that prenatal caffeine exposure is associated with an enduring tendency toward a profile of fearfulness, hypoactivity, and exaggerated stress in uncertain situations. A similar pattern of behavioral inhibition has been observed in humans and has been attributed to various causes such as inborn temperament or environmental influences. The author's conjecture is that prenatal caffeine exposure could be an additional factor contributing to the tendency toward behavioral inhibition. One mechanism for this effect is that caffeine causes an upregulation of adenosine receptors, thus creating a vulnerability to adenosine-induced inhibition of neuronal firing and neurotransmitter release.

Shyness and little boy blue: iris pigmentation, gender, and social wariness in preschoolers

In recent years, researchers have uncovered a link between iris pigmentation and inhibition/social wariness among young children (e.g., Rosenberg & Kagan, 1987, 1989; Rubin & Both, 1989). In the present study, 152 Caucasian preschool-aged (Mage = 54.09 months, SD = 5.84) children (77 males) with either blue (n = 84) or brown (n = 68) eyes, were compared in terms of parental and teacher ratings of social wariness, social play, and aggression. A significant Eye Color x Gender Interaction was found in terms of indices of social wariness; blue-eyed males were rated as more socially wary than brown-eyed males, while blue- and brown-eyed females did not differ in this regard. These results supported the notion that eye color is a marker variable for social wariness in young children.

Vascular disease risk factors, urinary free cortisol, and health histories in older adults: shyness and gender interactions

We studied relationships between shyness and health during a health screening survey of older adults (ages 50-88) living in an active retirement community in the southwestern United States (n = 232). As in previous studies of infants, older individuals with hay fever, insomnia and constipation were more shy than those without these problems. Shy persons overall showed higher sitting systolic blood pressure and a larger fall in orthostatic systolic blood pressure on standing; shy men had a greater prevalence of hypertension histories than did low-shy men. Shy subjects of both sexes had lower HDL cholesterol and higher triglycerides than did low-shy subjects; shy women tended to have higher LDL cholesterol than did low-shy women. In contrast with findings of elevated salivary cortisol in extremely inhibited children of both sexes, only shy women had higher 24 h urinary free cortisol excretion than did low-shy women; men showed the opposite pattern, possibly related to suppression of aggression. Shy men also tended to report a higher prevalence of thyroid disease history than did low-shy men (20% versus 6%). Notably, autoimmune thyroiditis has previously been linked with panic and depression, disorders which in turn have been associated with shyness. Taken together with previous work in shy children and their families, the data raise the possibility of (a) increased risk for arteriosclerotic vascular disease; and (b) increased risk of adrenal- and/or thyroid-related diseases in certain shy older adults.

Relation of eye color and gender to Type A scores and vocational preference

Type A behavior scores on the Jenkins Activity Survey, Form T, and ACT Interest Inventory data were collected for 90 male and 90 female university students who equally represented three eye-color groups, black/brown, blue, and other. Chi-squared analyses indicated no statistically significant associations at the .05 level. Observations which may be of interest to researchers are noted.

Physical and physiological correlates of behavioral inhibition

Previous investigations have suggested that the temperamental quality of inhibition is related to the threshold of reactivity to unfamiliar events within certain limbic structures. In earlier work, children in three independent samples who had been selected to be inhibited were more likely to have blue than brown eyes, whereas uninhibited children were more likely to have brown eyes. The present study, which selected two-year-old children on the basis of eye color (blue or brown) rather than behavior, found a significant association between blue eyes and behavioral inhibition, and between brown eyes and an uninhibited style. Although the inhibited children were more likely to have a high and stable heart rate than were the uninhibited children, there was no relation between eye color and these cardiac measures. Several interpretations of the association between these temperamental categories and iris pigmentation are proposed.

Iris pigmentation and sociability in childhood: a re-examination

Drawing from Rosenberg and Kagan's (1987) finding of an association between iris pigmentation and behavioral inhibition in early childhood, we sought, in the present investigation, to examine the developmental relation between eye color and social withdrawal in kindergarteners and children in grades 2 and 4. In kindergarten and grade 2, blue-eyed children were found to be overrepresented in groups of extremely withdrawn youngsters. No association was found between eye color and withdrawal in grade 4 or between eye color and extreme sociability at any grade. The results were interpreted as suggestive of the increasing role, with age, of social factors in the determination of extremely inhibited behavior.