Explain Sex Differences Research Articles

E-Health? Clinical information network interest and impediments in a community paediatric setting

Increased interest in implementing evidence-based medicine in paediatric practice has led to the development of a variety of electronic clinical and decision-making support tools. Electronic medical records and information resources have the potential to improve both the clinical and cost effectiveness of paediatric community practice at the point of care. Barriers to the successful implementation of clinical information Intranet resources include physician attitudes, as well as system and practitioner capabilities. To examine Ontario's community care paediatricians' electronic information resource needs and interest in accessing the proposed Central West Ontario Pediatric Information Network (CWPIN). Cross-sectional, interviewer-facilitated, structured survey. Paediatricians providing community care in the Central West Ontario Health Region. Three-quarters of regional community paediatricians responded to the survey. Of those surveyed, 98% expressed interest in gaining access to the CWPIN. Computer literacy, suggested by home computer and Internet use rates (88% and 81%, respectively), did not differ significantly by age or sex. Other factors that may affect network use, such as workplace computer use and allied personnel role assignment, differed by sex, indicating potentially greater CWPIN use among male practitioners. Physicians reported an overwhelming interest in gaining access to and using the CWPIN. Disparities in current workplace but not home-based computer use by sex indicate that workplace role allocation, rather than computer literacy, may explain sex differences in CWPIN use rates. Attitudinal and computer proficiency issues did not appear to be obstacles to implementing the clinical information Intranet resource in the region.

Small Business Success in Rural Communities: Explaining the Sex Gap*

Abstract Building on previous theory and research, we propose a “structural relational” view of the sex gap in small business success. Our findings, based on analyses of data from 423 small business owners in Iowa, show support for our model and suggest that links between owners, social relational processes, business structure, and small business success operate differently depending on the industry location of the business and the owner's sex. Results also indicate that the business owner's sex has direct and indirect effects on business success. This finding suggests that social relations, organizations, and institutions are all gendered in ways that influence the sex gap in sales, but that further research is needed to more fully explain sex differences in small business success. We discuss these and other findings in terms of their theoretical and practical implications, and suggest directions for future research.

Sex, gender, and blood pressure: contributions to experimental pain report.

The current study investigated whether the relationship between sex and experimental pain report was explained by systolic blood pressure (SBP) at rest or during pain task, by gender-role socialization as assessed by the Bem Sex Role Inventory, or both. The influence of gender-role socialization on pain report is often inferred but rarely studied. Fifty female and 54 male healthy, young adults completed the Bem Sex Role Inventory and then underwent a cold pressor task. Blood pressure was assessed before and during pain testing. Univariate analyses indicated significant sex-related differences in pain threshold and pain tolerance. Baseline SBP was positively related to pain tolerance but did not explain sex differences, in accord with previous research. The Bem Sex Role Inventory demonstrated a relationship with pain, but did not explain sex differences. We suggest that context-specific measures of gender are needed to assess gender-related pain behaviors in specific situations. Results from the current study support our contention that gender is part of sex as commonly measured. Also, blood pressure does not appear to fully account for sex-related differences in pain.

Testing Stereotype Threat: Does Anxiety Explain Race and Sex Differences in Achievement?

Steele's (1992, 1997) stereotype-threat theory attempts to explain underperformance of minority students in academic domains and of women in mathematics. Steele argues that situational self-relevance of negative group stereotypes in testing situations increases the anxiety these students experience and that these differential anxiety levels explain performance differences. Research shows that manipulation of stereotype threat can affect academic performance. However, there has been little research testing whether anxiety does at least partially explain the relationship between race and achievement. The goal of this study was to examine whether anxiety will explain racial differences in academic performance and gender differences in math performance in the context of a nationally representative sample of high school seniors. Partial mediation was observed, with anxiety explaining significant portions of the racial differences in academic performance. Anxiety also partially explained sex differences in math achievement, although the effect sizes were very small. These results provide general support for Steele's stereotype-threat hypothesis.

Cognitive function in the oldest old: women perform better than men

OBJECTIVELimited formal education is associated with poor cognitive function. This could explain sex differences in cognitive function in the oldest old. Whether limited formal education explains differences in cognitive function...

Venous Pressure Dynamics of the Healthy Human Leg

The delicate interplay between the muscle-joint unit and intact venous valves is mandatory for normal venous blood return from the human leg. We have investigated the potential role of (1) muscle activity and joint mobility, and (2) anthropometric factors for peripheral venous pressure physiology. 20 healthy young subjects (10 males, 10 females; mean age: 25.6 ± 3.1 years) underwent direct venous blood pressure measurements during walking on a treadmill in 12 experimental conditions (duration, 1 min each): these resulted from a combination of two different walking velocities, two different degrees of ascent, and three different walking conditions. Anthropometric parameters (e.g., body height, weight and calf circumference) were also measured in all subjects. Outcome measures were the pressures (mm Hg) during quiet standing (resting pressure, P₀), the maximal activity-induced pressure reduction (ΔP_max), i.e., the difference between the resting pressure (P₀) and minimal pressure during exercise (P_min), the times (s) to minimal pressure during exercise (T_Pmin) and to half-maximal recovery of P₀ after exercise (T_max1/2). We found that the maximal venous pressure reduction (ΔP_max) during walking increased at the higher walking speed and decreased with restricted joint mobility (p = 0.0001). Taller and heavier subjects, or subjects with a greater calf circumference had higher P₀ (p = 0.0001), showed greater ΔP_max (p < 0.010), and took longer to achieve minimal pressure during exercise (T_Pmin; p < 0.010) than their corresponding counterparts. Females had lower levels of P₀ (p = 0.0001), but not of ΔP_max, and shorter T_Pmin (p = 0.0076) than males. These gender effects largely result from differences in body height, weight, and calf circumference (p = 0.0001 for the appropriate ANOVA interaction terms). We conclude that during walking, a higher degree of muscle activity and a greater muscle mass enhance venous emptying of the healthy human leg. Conversely, impairments of joint mobility reduce the efficacy of the muscle-vein pump. Moreover, body height and weight significantly influence venous pressure physiology under both resting and activity-related conditions. These anthropometric factors also largely explain sex differences in peripheral venous hemodynamics.

Lateralization and effects of adult androgen in a sexually dimorphic neuromuscular system controlling song in zebra finches

Unlike many other sexually dimorphic systems, gonadal secretions do not explain sex differences in the morphology of the telencephalic song control nuclei of zebra finches. It is important to understand whether a novel mechanism for controlling structure is restricted to the forebrain regions specialized for song, and whether other areas respond more typically to gonadal steroids. Therefore, the effects of sex and adult androgen manipulation on the neuromuscular end of the song control system (tracheosyringeal portion of the hypoglossal nucleus, nXIIts, and the syrinx, or vocal organ) were investigated. Because lesion and axotomy experiments indicate a right-side bias in the functional control of song, asymmetry in the motor nucleus and in the ventralis and dorsalis syrinx muscles was also tested. Male-biased dimorphisms existed in the volume of nXIIts, and in syrinx mass and size of muscle fibers, but not in motoneuron number or size. Asymmetries favoring the right side were detected in nXIIts volume and motoneuron number in males, as well as in ventralis and dorsalis fiber size in both sexes. Hormone manipulations had no effect on nXIIts size, neuron size, or number. Testosterone treatment of adult females increased all of the syringeal measures, but the only effect of flutamide in males was to decrease syrinx weight. Thus, male-biased sexual dimorphisms and right side dominance in both nXIIts and the syrinx may facilitate singing behavior. Adult androgen exposure can induce partial masculinization of the syrinx, but other factors must be important in mediating the sex differences in both that structure and the volume of nXIIts. J. Comp. Neurol. 426:154–164, 2000. © 2000 Wiley-Liss, Inc.

Generating Sexually Differentiated Vocal Patterns: Laryngeal Nerve and EMG Recordings from Vocalizing Male and Female African Clawed Frogs (Xenopus laevis)

Male and female African clawed frogs (Xenopus laevis) produce sexually dimorphic vocalizations; for males these include advertisement, amplectant, and growling calls, whereas female calls include ticking. Previous studies have shown that the vocal organ, the larynx, of the sexes differs in physiological properties that parallel vocal differences. However, it was not clear whether these characteristics are sufficient to explain sex differences in vocal behavior. To examine the contribution of the CNS to generating vocal patterns, we developed a preparation in which both laryngeal nerve activity and electromyograms can be recorded from awake, vocalizing frogs. Recordings reveal that the CNS of the two sexes produces patterned activity that closely matches each vocalization whereas the larynx faithfully translates nerve activity into sound. Thus, the CNS is the source of sexually differentiated vocalizations in Xenopus laevis. Furthermore, detailed analyses of compound action potentials recorded from the nerve lead us to hypothesize that neuronal activity underlying different male call types is distinct; some calls are likely to be generated by synchronous firing of motoneuron populations of either constant size or progressively larger sizes, whereas others are generated by asynchronous activity of motoneurons, a pattern shared with vocal production in females. We suggest that these distinct neuronal activity patterns in males may be subserved by two populations of motor units in males that can be distinguished by the strength of the neuromuscular synapse.

Imprinting, the X-chromosome, and the male brain: explaining sex differences in the liability to autism.

Males are at least four times more likely to develop autism than females. Among relatives with a broader autistic phenotype, males predominate too. Autism is a highly heritable disorder, yet genome scans have not revealed any predisposing loci on the sex chromosomes. A nongenetic explanation for male vulnerability, such as exposure to prenatal androgens, is unlikely for a variety of reasons. A novel genetic mechanism that resolves many of the outstanding difficulties is outlined here. The imprinted-X liability threshold model hypothesizes that the threshold for phenotypic expression of many autistic characteristics is influenced by an imprinted X-linked gene(s) that is protective in nature. Imprinted genes are known to play an important role in normal fetal and behavioral development. The gene is expressed only on the X-chromosome that is inherited from the father and raises the threshold for phenotypic expression. It is normally silenced when transmitted maternally. Because only females have a paternal X-chromosome, the threshold for phenotypic expression is higher in them than in males. Evidence for the existence of the genetic locus was found in a study of females with X-monosomy (Turner's syndrome) in which females had either a single paternal or maternal X-chromosome. Identifying the sites of action of this X-linked gene could lead to the discovery of autosomal loci that confer more directly a predisposition to autism.

Lateralization and effects of adult androgen in a sexually dimorphic neuromuscular system controlling song in zebra finches

Unlike many other sexually dimorphic systems, gonadal secretions do not explain sex differences in the morphology of the telencephalic song control nuclei of zebra finches. It is important to understand whether a novel mechanism for controlling structure is restricted to the forebrain regions specialized for song, and whether other areas respond more typically to gonadal steroids. Therefore, the effects of sex and adult androgen manipulation on the neuromuscular end of the song control system (tracheosyringeal portion of the hypoglossal nucleus, nXIIts, and the syrinx, or vocal organ) were investigated. Because lesion and axotomy experiments indicate a right-side bias in the functional control of song, asymmetry in the motor nucleus and in the ventralis and dorsalis syrinx muscles was also tested. Male-biased dimorphisms existed in the volume of nXIIts, and in syrinx mass and size of muscle fibers, but not in motoneuron number or size. Asymmetries favoring the right side were detected in nXIIts volume and motoneuron number in males, as well as in ventralis and dorsalis fiber size in both sexes. Hormone manipulations had no effect on nXIIts size, neuron size, or number. Testosterone treatment of adult females increased all of the syringeal measures, but the only effect of flutamide in males was to decrease syrinx weight. Thus, male-biased sexual dimorphisms and right side dominance in both nXIIts and the syrinx may facilitate singing behavior. Adult androgen exposure can induce partial masculinization of the syrinx, but other factors must be important in mediating the sex differences in both that structure and the volume of nXIIts.

Sekseverschillen in interactiegedrag: een verschuiving in verklaringsparadigma's

Men and women communicate in different ways. Their interaction patterns differ at both the verbal and the nonverbal level. Next to descriptive analysis, research has also aimed to explain sex differences in interaction behaviour. The oldest explanatory paradigm, “the dominance approach’, considers women as a suppressed group. In this view, sex differences in communication behaviour can be attributed to male dominance and female subordination. However, in the past 10 years, the dominance approach is being questioned and is increasingly replaced by the “difference approach’. This model emphasises the idea that men and women are socialised in two different subcultures and consequently develop different interaction patterns.

Explaining Sex Differences in Educational Choice An Empirical Assessment of a Rational Choice Model

Sex segregation with regard to choice of type of education, or educational programme, is persistently high in Sweden, while men and women nowadays reach similar levels of education. In order to explain this phenomenon, a rational choice model is proposed in which sex-specific comparative advantages in different fields of study are in focus. Such relative advantages in sex-typical areas of study are hypothesized to influence educational choices through their effects on the expected probabilities of success in different study programmes. The theoretical model explains sex differences very well when judged against aggregate data, but empirical analyses on micro-level data are less supportive of the underlying hypothesis. While indicators of both absolute and relative school achievements are powerful predictors of educational choice, boys and girls with similar 'ability profiles' largely follow sex-typical choice patterns. Comparative advantages may 'account for' 10 to 30 per cent of the sex effect on educational choice at the upper secondary level of education in Sweden. The paper concludes with a short discussion of alternative explanations.

Parental investment, potential reproductive rates, and mating system in the strawberry dart-poison frog, Dendrobates pumilio

We studied the effect of relative parental investment on potential reproductive rates (PRRs) to explain sex differences in selectivity and competition in the dart-poison frog Dendrobates pumilio. We recorded the reproductive behavior of this species in a Costa Rican lowland rainforest for almost 6 months. Females spent more time on parental care than males, and `time out' estimates suggest that PRRs of males are much higher than than those of females, rendering females the limiting sex in the mating process. Males defended territories that provide suitable calling sites, space for courtship and oviposition, and prevent interference by competitors. Male mating success was highly variable, from 0 to 12 matings, and was significantly correlated with calling activity and average perch height, but was independent of body size and weight. Estimates of opportunity for sexual selection and variation in male mating success are given. The mating system is polygamous: males and females mated several times with different mates. Females were more selective than males and may sample males between matings. The discrepancy in PRRs between the sexes due to differences in parental investment and the prolonged breeding season is sufficient to explain the observed mating pattern i.e., selective females, high variance in male mating success, and the considerable opportunity for sexual selection.

The last days of discord? Evolution and culture as accounts of female–female aggression

When aggression is conceptualised in terms of a cost-benefit ratio, sex differences are best understood by a consideration of female costs as well as male benefits. Benefits must be extremely high to outweigh the greater costs borne by females, and circumstances where this occurs are discussed. Achievement of dominance is not such a circumstance and evidence bearing upon women's egalitarian relationships is reviewed. Attempts to explain sex differences in terms of sexual dimorphism, sex-of-target effects, social control, and socialisation are found to be inadequate. The suggestion that the stigmatisation of female aggreession arises not from patriarchal imposition but from statistical rarity (resulting from evolutionary pressures) is given serious consideration. Two hypotheses (“internal read-out” versus social/epidemiological representations) are described to explain the relationship between sex differences in behaviour and corresponding lay explanations.

Sex differences in opioid analgesia: Of mice and women

I n their Focus article, Miaskowski and Levine advance the hypothesis that women display greater opioid analgesia than men. Their conclusions are largely based on studies of patient-controlled analgesia (PCA) and their own studies of postoperative dental pain. In sum, these findings can be construed as being contrary to the bulk of the existing animal literature. We would like to present some recent data that bear upon the apparent inconsistencies in the animal literature regarding the direction and variability of sex differences. Furthermore, we would like to offer another interpretation of the investigators' findings that kappa-opioids may be more effective analgesics in women. As presented by Miaskowski and Levine, overwhelming evidence exists that in rats and mice, when differences are found, the potency and efficacy of opioid agonists such as morphine are higher in males. Differential morphine pharmacokinetics do not adequately explain sex differences in the animal literature, as such differences persist after central administration of opioid agonists [2,9]. Although quite a few studies fail to observe sex differences, to our knowledge, only one study has ever reported a significant female greater than male difference in opioid analgesia [1]. It can be argued that many of the animal studies are limited by their use of single doses and/or single time points [1], and that variation in nociceptive assay, time of day, hormonal status, and subject age can affect the presence of sex differences. However, Miaskowski and Levine describe the human studies in this field as equally beset by

Regulation of gene expression by corticoid hormones in the brain and spinal cord

Glucocorticoids (GC) and mineralocorticoids (MC) have profound regulatory effects upon the central nervous system (CNS). Hormonal regulation affects several molecules essential to CNS function. First, evidences are presented that mRNA expression of the α3 and β1-subunits of the Na,K-ATPase are increased by GC and physiological doses of MC in a region-dependent manner. Instead, high MC doses reduce the β1 isoform and enzyme activity in amygdaloid and hypothalamic nuclei, an effect which may be related to MC control of salt appetite. The α3-subunit mRNA of the Na,K-ATPase is also stimulated by GC in motoneurons of the injured spinal cord, suggesting a role for the enzyme in GC neuroprotection. Second, we provide evidences for hormonal effects on the expression of mRNA for the neuropeptide arginine vasopressin (AVP). Our data show that GC inhibition of AVP mRNA levels in the paraventricular nucleus is sex-hormone dependent. This sexual dimorphism may explain sex differences in the hypothalamic–pituitary–adrenal axis function between female and male rats. Third, steroid effects on the astrocyte marker glial fibrillary acidic protein (GFAP) points to a complex regulatory mechanism. In an animal model of neurodegeneration (the Wobbler mouse) showing pronounced astrogliosis of the spinal cord, in vivo GC treatment down-regulated GFAP immunoreactivity, whereas the membrane-active steroid antioxidant U-74389F up-regulated this protein. It is likely that variations in GFAP protein expression affect spinal cord neurodegeneration in Wobbler mice. Fourth, an interaction between neurotrophins and GC is shown in the injured rat spinal cord. In this model, intensive GC treatment increases immunoreactive low affinity nerve growth factor (NGF) receptor in motoneuron processes. Because GC also increases immunoreactive NGF, this mechanism would support trophism and regeneration in damaged tissues. In conclusion, evidences show that some molecules regulated by adrenal steroids in neurons and glial cells are not only involved in physiological control, but additionally, may play important roles in neuropathology.

Sex Difference in the Size of the Neural Song Control Regions in a Dueting Songbird with Similar Song Repertoire Size of Males and Females

Previous studies have suggested a causal relation between sex differences in behavior such as singing and sex differences in the size of brain areas such as the forebrain song control areas of songbirds. In the present study we show that the size of the forebrain vocal control areas nucleus hyperstriatalis ventrale pars caudale (HVC) and nucleus robustus archistriatalis (RA) and its neuron numbers are about twice as large in males as in females of the African dueting bush shrike Laniarius funebris. However, song types are of similar complexity (number of elements per song type, physical properties of elements) in both sexes, and repertoire size does not differ between males and females. Furthermore, in captivity male and female shrikes are able to learn the same song types. This demonstrates for the shrike that sex differences in the size of vocal control areas and in its neuron numbers do not predict the type of sex-typical vocal behavior. This result is supported by a statistical comparison of the sex differences in HVC size, RA size, and song repertoire size of all songbird species studied to date. Sex differences in species in which only the males sing are indeed larger than in species in which the females also sing; in songbird species with singing females, however, the sex differences in HVC and RA volume appear to be independent of the vocal repertoire size of females. The songbird model therefore does not support the notion that sex differences in area size and neuron number explain sex differences in a behavior that occurs in both sexes. Furthermore, in the shrike, neuron soma size is similar in males and females in the song motonucleus hypoglossus pars tracheosyringealis (nXIIts) and in the premotor nucleus RA, but is sexually dimorphic in the higher vocal center HVC. Thus, male and female shrikes produce songs of similar complexity with different neuron phenotypes.

Drivers of Intelligence Evolution in Homo: Sexual Behavior, Food Acquisition and Infant Neoteny

There are many hypotheses on language and IQ evolutions, but many failed to explain sex differences of IQ. Some discussions presuppose that only Homo has language and that this appeared suddenly. Molecular level evolution does not support any sudden appearance of language. Bipedality amongst Homo was a factor in the evolution of many modem aspects of Homo; changes in copulation behavior contributed to the evolution of language; bipedality produced a larger brain, but blocked enlargement of the parturient canal and retarded further increases in the size of the brain. The female Homo was forced to deliver the neonate in a state of neoteny. Females further evolved language in order to take care of the infants. Male Homos accelerated food acquisition activities to provide the energy required to maintain a larger brain. The male Homo lost the initiative in sexual intercourse at female's mating season and began to depend on language from the female as a signal for mating. Females who acquired the initiative in copulation begun to select male partners by their ability to provide food and security. By this sexual selection, the evolution of language was accelerated. Neoteny, although physically disadvantageous, assisted neural development. Homo developed the ability to accumulate more information, a process in which language played a crucial role. Key Words: Homo Sapiens, evolution, language, neural development, intelligence, bipedality, copulation. Introduction Although there have been hypotheses on evolution of language which comprises a quite important part of intelligence, many of these explained this evolution in terms of early human collaboration for the purpose of hunting, escaping from dangerous animals, and other production activities which were primarily engaged in by males (Kimura, 1987). The hypotheses failed to explain the sex differences in verbal and performance IQs as reported by many researchers (Rushton, 1992; Halpern, 1996, 1997; Lynn, 1996; Lynn, 1998; Sanders & Wright, 1997). In addition to the psychometric data on sex difference, there is evidence of sex differences in brain anatomy (Reiss, et al., 1996; Shaywitz, et al., 1995; Sanders, 1998). Evolution of performance IQ is explainable by hunting and other production activities, but that of verbal IQ is not explicable by production activities. The higher verbal IQ of females and the common sense of talkative females must be explained by evolution pressure on females. In the beginning was the word! There are researchers who consider that language is a unique ability acquired only by mankind (Chomsky, 1988; Pinker, 1994). These researchers believe that language appeared very recently in the history of the evolution, as a result of one or more sudden mutations. However, molecular genetics does not support such rapid evolution by mutation. Mutations are almost always dangerous for the existence of a species, and the probability that positive, not dangerous, changes result from any specific mutation is extremely small. Molecular genetics confirms that the evolution of language did not happen suddenly. Behavioral level evolutional hypotheses should be consistent with the evidence provided by molecular evolution. This paper discusses presuppositions which should be considered in building evolutional hypotheses consistent with molecular genetics, then presents hypotheses concerning the possible evolution of sex difference in intelligence. Molecular-Level Evolution Leakey (1994) summarized three hypotheses on the evolution of languare proPosed from the archeological, brain-anatomical, and speech-organic points of views. (a) From archeological remains it is hypothesized that language ability appeared at the early stage in the evolution of Homo, stayed at a relatively lower functional level during most of the prehistoric era, and drastically improved in more recent times. (b) From the anatomical evidence of the brain it is hypothesized that language ability evolved gradually. …

ESTRADIOL AND PROGESTERONE ALTER ETHANOL-INDUCED EFFECTS ON μ-OPIOID RECEPTORS IN SPECIFIC BRAIN REGIONS OF OVARIECTOMIZED RATS

This study was conducted to evaluate the effects of estradiol and progesterone on ethanol-induced alterations of μ-opioid receptor binding kinetics in specific brain regions. Female ovariectomized rats were injected with ethanol (3 g/kg, i.p.), estradiol (50 μg/kg, s.c.) and/or progesterone (5 mg/kg, s.c.), or ethanol plus estradiol and/or progesterone daily for 7 days. Control animals received saline and olive oil. Brains were immediately removed and the cortex, hippocampus, hypothalamus, and midbrain were dissected and assayed for μ-opioid receptor binding kinetics. In the hypothalamus, ethanol alone and in combination with estradiol and/or progesterone significantly decreased B max. Ethanol alone also decreased B max in the midbrain and cortex. When administered with estradiol only, ethanol increased B max and K d in the hippocampus. The administration of estradiol alone and progesterone alone decreased B max in the hypothalamus, while not affecting B max in any of the other brain regions. However, when estradiol and progesterone were combined, B max, as well as K d, increased in the cortex. Progesterone alone and in combination with estradiol also increased K d in the midbrain. In addition, K d significantly increased following administration of ethanol in combination with either of the hormones, or both, in the midbrain and cortex. These results clearly indicate that the female hormones modulate the effects of ethanol on binding kinetics of μ-opioid receptors in specific brain regions. The present findings may in part explain sex differences in alcohol effects.

Gender, Children, and Social Contact: The Effects of Childrearing for Men and Women

The authors investigate the impact of childrearing on men's and women's social networks, using a probability sample of residents of 10 Great Plains towns. Data support the hypotheses that social network size, contact volume and composition vary with the age of the youngest child in a family. Childrearing reduces women's network size and contact volume, while it alters the composition of men's networks. Effects are most pronounced when the youngest child is around three years old. These results suggest the possibility that sex differences in structural location (in the sense of embeddedness in social networks) explain sex differences in outcomes over the life course. The gender-specific effects of this life stage may accrue because childrearing places men and women in separate social worlds; childbearing and childrearing thus may be a crucial phase in the process by which gender differences are created and maintained