Male and female twins with opposite-sex co-twins were compared to twins with same-sex co-twins on three independent dimensions of masculinity-femininity, in order to examine the hypothesis that the hormones of the co-twin might have an effect on prenatal masculinization. The analysis was originally carried out for an older cohort from the Australian Twin Registry (2647 pairs, mean age 41.2), an...

tions to address vitamin A deficiency (by increasing frequent low-level vitamin A intakes) together with continued targeted use of high-dose VACs for those who would benefit. However, we would again like to stress that, since VACs are distributed to 1–5-year-old children, they are not relevant to the majority of under 5-year-old deaths (U5MR), which are predominantly in the first few months of ...

The present study investigates the demographics of same-sex marriages--that is, registered partnerships-in Norway and Sweden. We give an overview of the demographic characteristics of the spouses of these partnerships, study patterns of their divorce risks, and compare the dynamics of same-sex couples with those of heterosexual marriages. We use longitudinal information from the population regi...

Diagnosis of a major depressive episode by the Diagnostic and Statistical Manual of Mental Disorders of the American Psychiatric Association requires 5 out of 9 symptoms to be present. Therefore, individuals may differ in the specific symptoms they experience and reach a diagnosis of depression via different pathways. It has been suggested that depressed women more often report symptoms of slee...

BACKGROUND Sex differences in structural birth defects are often confounded by environmental risk factors. Opposite-sex twins provide a unique model for detecting sex differences in birth defects while maximally controlling environmental risk factors in a natural setting. METHODS Population data from the Florida Birth Defects Registry were analyzed. A total of 4,768 pairs of twins who were di...

The purpose of this study was to determine whether pre-adolescents interacted more similarly and more positively in best friend pairs than those in acquaintance pairs and whether same-sex dyads interacted more similarly and more positively than opposite-sex dyads. Archival videotapes were coded for the face-to-face interaction behaviors of preadolescent best friend and acquaintance dyads and sa...

Social integration and support can have profound effects on human survival. The extent of this phenomenon in non-human animals is largely unknown, but such knowledge is important to understanding the evolution of both lifespan and sociality. Here, we report evidence that levels of affiliative social behaviour (i.e. 'social connectedness') with both same-sex and opposite-sex conspecifics predict...