Sex Differences in Normal Fetuses and Infants: A Commentary

Dyadic parent-infant interaction patterns at 12 months: Exploring dyadic parent-infant gender compositions

This study investigates differences in dyadic mother-infant and father-infant interaction patterns at infant age 12 months, and the relation between different parent-infant gender compositions and the dyadic interaction. Data were drawn from a large-scale, population-based Norwegian community sample comprising 671 mother-infant and 337 father-infant interactions. The Early Relational Health Screen (ERHS), a screening method for observing dyadic parent-infant interactions, was used to assess the parent-infant interactions. Scores on the ERHS were employed to investigate dyadic differences in the overall interaction scores, and dyadic interaction on seven sub-dimensions between mother-infant and father-infant pairs. The relation between different parent-infant gender compositions and the dyadic interaction scores was also examined. As expected in a normative sample, most parent-infant interactions received scores in the upper rating levels. Differences between mother-infant and father-infant patterns were generally small, but mother-infant dyads tended to obtain slightly higher scores. The mother-infant dyads received higher scores on the dimensions of engagement and enjoyment, but no other significant differences between the parent-infant pairs were found for the remaining dimensions. We did not find evidence for a moderation effect of child gender. However, parent-daughter dyads received somewhat higher scores than the parent-son dyads.

The development of mental rotation ability across the first year after birth

Mental rotation (MR) is the ability to imagine the appearance of an object from a different perspective. This ability is involved in many human cognitive and behavioral activities. We discuss studies that have examined MR in infants and its development across the first year after birth. Despite some conflicting findings across these studies, several conclusions can be reached. First, MR may be available to human infants as young as 3 months of age. Second, MR processes in infancy may be similar or identical to MR processes later in life. Third, there may be sex differences in MR performance, in general favoring males. Fourth, there appear to be multiple influences on infants' MR performance, including infants' motor activity, stimulus complexity, hormones, and parental attitudes. We conclude by calling for additional research to examine more carefully the causes and consequences of MR abilities early in life.

Spatial Thinking in Infancy: Origins and Development of Mental Rotation Between 3 and 10 Months of Age

Mental rotation (MR) is the ability to transform a mental representation of an object so as to accurately predict how the object would look from a different angle (Sci 171:701–703, 1971), and it is involved in a number of important cognitive and behavioral activities. In this review we discuss recent studies that have examined MR in infants and the development of MR across the first year after birth. These studies have produced many conflicting results, yet several tentative conclusions can be reached. First, MR may be operational in infants as young as 3 months of age. Second, there may be sex differences in MR performance in infancy, in general favoring males, as there are in children and in adults. Third, there appear to be multiple influences on infants’ MR performance, including infants’ motor activity, stimulus or task complexity, hormones, and parental attitudes. We conclude by calling for additional research to examine more carefully the causes and consequences of MR abilities early in life.

Sex differences in nonhuman primate behavioral development

Sex differences in behavior and developmental trajectories in human children are of great interest to researchers in a variety of fields, and a persistent topic of discussion and debate is the relative contribution of biological vs. social influences to such differences. Given the potentially large effects of cultural and social influences on human child development, nonhuman primates are important model species for investigating the biological and evolutionary roots of sex differences in human development. This Mini-Review briefly summarizes the existing literature on sex-biased behavior toward infant nonhuman primates by mothers and other social partners, followed by a review of findings on sex differences (or lack thereof) in primate behavioral development from a variety of species in wild and naturalistic settings. These include differences in physical and social development, including play, grooming, and object manipulation patterns, as well as nursing and the development of foraging behavior. The Mini-Review concludes by providing potential avenues for future research. © 2016 Wiley Periodicals, Inc.

ASSOCIATIONS BETWEEN EARLY MATERNAL DEPRESSIVE SYMPTOM TRAJECTORIES AND TODDLERS' FELT SECURITY AT 18 MONTHS: ARE BOYS AND GIRLS AT DIFFERENTIAL RISK?

The goal of this study was to evaluate whether there are sex differences in children's vulnerability to caregiving risk, as indexed by trajectories of maternal depressive symptoms assessed from 2 to 18 months' postpartum, and children's rated attachment security in toddlerhood, adjusting for maternal social support and demographic risk. Analyses utilized longitudinal data collected for 182 African American mother-child dyads from economically diverse backgrounds. Participants were recruited at the time of the child's birth and followed to 18 months' postpartum. Results of conditional latent growth models indicated that an increasing rate of change in level of maternal depressive symptoms over time negatively predicted toddlers' felt attachment security. Higher social support was associated with decreasing levels of maternal depressive symptoms over time whereas higher demographic risk was associated with increasing levels of maternal depressive symptoms. A subsequent multigroup conditional latent growth model revealed that child sex moderated these associations. For male (but not female) children, a rapid increase in maternal depressive symptoms was associated with lower felt attachment security at 18 months. These findings suggest that boys, as compared to girls, may be more vulnerable to early caregiving risks such as maternal depression, with negative consequences for mother-child attachment security in toddlerhood.

Experience-independent sex differences in newborn macaques: Females are more social than males

Human females exhibit greater social interest and skills relative to males, appearing in infancy, suggesting biological roots; however, male and female infants may be treated differently, potentially causing or amplifying sex differences. Here, we tested whether sex differences in social motivation emerge in infant monkeys (n = 48) reared in a controlled postnatal environment. Compared to males, females at 2-3 weeks looked more at conspecifics' faces (d = 0.65), especially the eyes (d = 1.09), and at 4-5 weeks exhibited more affiliative behaviors (d = 0.64), including gesturing, looking, and proximity to familiar and unfamiliar human caretakers. In sum, converging evidence from humans and monkeys suggests that female infants are more social than males in the first weeks of life, and that such differences may arise independent of postnatal experience. Individual differences in social interest have wide-ranging developmental consequences, impacting infants' social interaction quality and opportunities for learning. Understanding the evolution of sex differences and their developmental emergence is necessary to best support infants with varying levels of sociality.